~
Quaternary.ScienceReviews,Vol. 16, pp. 793-819, 1997.
tP e r g a m o n
PIh S0277-3791(97)00023-1
© 1997Elsevier Science Ltd.
All rights reserved. Printed in Great Britain
0277-3791/97 $32.00
JOKULHLAUP DEPOSITS IN PROGLACIAL AREAS
JUDITH
MAIZELS
Department of Geology and Geophysics, Grant Institute, University of Edinburgh, West Mains Road, Edinburgh
EH9 3JW, U.K.
A b s t r a c t - - This paper discusses the main causes and characteristics of j6kulhlaup ('glacier burst')
floods, and explores the extent to which they generate depositional landform and sediment
assemblages that are distinct from those of 'normal', braided river outwash ('Type l' outwash). Two
main jrkulhlaup outwash environments are identified: Type II outwash, produced by sudden
drainage of ice-dammed lakes; and Type III, associated with drainage during subglacial geothermal
activity, and distinguished by deposits resulting from high sediment concentrations and
hyperconcentrated flows.
In fluid flows, especially ones yielding Type II outwash, the most common deposits are largescale expansion bars (and locally, eddy and pendant bars), and 'mega-ripples' or dunes, both forms
normally composed of large-scale gravel-cobble cross-bedding, often capped by an imbricated
boulder lag (a 'Type B2' lithofacies sequence). The armour is absent only where runoff decreased
too rapidly to allow surface winnowing. Other j6kulhlaup facies include extensive boulder beds
(Type C), inverse-normally graded cobble beds (Type D5), ice-proximal debris flow deposits and
deformed bedding containing diamicton clasts (Types G and H), and slack-water sediments (Type
A). Type III outwash is dominated by massive, homogeneous, flood surge granules, underlain by
pre-surge gravels, and capped by post-surge fluid bedforms, reflecting deposition during both the
rising and falling limbs of the flood hydrograph (Type E4).
The paper demonstrates that jrkulhlaups do generate distinctive assemblages of depositional
landforms and sediments, and concludes with a model of the dominant lithofacies sequences and
associated landforms in proglacial environments subject to jrkulhlaup drainage. © 1997 Elsevier
Science Ltd
INTRODUCTION
QSR
This paper first examines the hydrologic and hydraulic characteristics of jrkulhlaup flows that control the
morphology and sedimentology of j6kulhlaup deposits
in subaerial proglacial fluvial environments; then summarises the main processes of deposition during jrkulhlaups, and reviews
the morphological
and
sedimentological characteristics of the resulting jrkulhlaup deposits. Finally, a classification of distinctive
jrkulhlaup lithofacies is proposed, together with a
framework for the palaeohydraulic and palaeoenvironmental interpretation of different jrkulhlaup sediment
sequences.
J6kulhlaup deposits, ranging from mega-scale ripples,
dunes and boulder bars to thick, stacked sequences of
hyperconcentrated sandur deposits, occur in many
proglacial environments. However, the criteria for
recognising j6kulhlaup deposits as such, and for differentiating them from non-flood outwash deposits, are only
poorly defined, hence their significance in aiding the
interpretation of palaeo-environmental changes during
deglaciation has often been underplayed. Glacial floods
can occur on a variety of time-scales, lasting for hours or
days, and recurring on annual, decadal or longer timescales. 'Glacier burst' floods or jrkulhlaups exhibit a
wide variety of flow characteristics, marked not only by
contrasts in flow magnitude, but also in the form, duration
and complexity of the flood hydrograph. In addition, the
sediment concentration of the flood can change significantly during different stages of flow. However, the
impact of a jrkulhlaup on the proglacial environment, and
on the depositional sequence in particular, reflects not
only these hydraulic criteria but also the nature of the
geomorphic constraints on the flood and the sensitivity of
the proglacial landscape to change.
HYDROLOGIC AND HYDRAULIC CONTROLS
ON JOKULHLAUP DEPOSITION: FLOW
CHARACTERISTICS
Causes of Jiikulhlaups
J6kulhlaups may be generated by a number of
different mechanisms, the most common of which is
failure of an ice dam which has acted to impound
an ice-marginal lake. J6kulhlaups may be triggered
by a number of other mechanisms, including water
793
794
Quaternat T Science Reviews." Volume 16
Geology
Topography
Climate
Glacier /
ice sheet
behaviour
/
-4
Sediment
availability
Sediment
concentration
I_
~ ~
I
I
I
I
Flood
routeway
Mechanism of
flood generation
Reservoir
characteristics
Channel
gradient
Flood
magnitude
Flood
frequency
Hydrograph
/
/I
~
F,ood
I
I
Flood
L
timing
Fluvial
hydraulics
Flowtype
and regime
Sediment
type
i
F
L~
Erosive
capacity
Extentof
flooding
Spatial
distribution
of flood
sediment
L
Vertical
sediment
sequence +
thickness
l
~_~
Erosive
landforms
Preservation
potential
Longterm
stratigraphy
FIG. I. Simplified model of the factors controlling flow and sediment characteristics of j6kulhlaup floods (modified from
Maizels and Russell, 1992).
overflowing an ice dam; rupture of subglacial, englacial
and supraglacial water bodies; sudden breaching of a
moraine or unconsolidated rock dam; rock falls or
ice avalanches on to the glacier; periods of extreme ice
melt; prolonged and heavy rainstorm events; glacier
surges; and periods of subglacial geothermal activity
or eruptions of subglacial volcanoes containing crater
lakes (e.g. Rist, 1983; Rc~thlisberger and Lang, 1987;
Church, 1988; Costa, 1988b)
Physical Controls on Jiikulhlaup Characteristics
The main controls on j6kulhlaup flow characteristics
and their potential geomorphic impact are illustrated in
the framework model (Maizels and Russell, 1992) (Fig. 1).
These controls are in turn dependent on the larger-scale
regional factors of geology, topography, climate, and
glacier or ice-sheet behaviour. The mechanism of
drainage and the reservoir characteristics largely control
J. Maizels: Jrkulhlaup Deposits in Proglacial Areas
the magnitude, frequency and timing of jrkulhlaups,
while the form of the hydrograph as it is propagated
downstream also reflects the morphology and gradient of
the flood routeway. Timing of the flood depends on the
source of the flood waters, as well as on the frequency of
flooding, and on rates of ice sheet or glacier ablation, lake
filling rates, and ice marginal fluctuations.
The availability of sediment to the flood waters affects
the sediment concentration of the flood which, when
combined with hydrograph and flood power characteristics, controls the hydraulics and flow regime of the
flood along its routeway - - i.e. the degree of turbulence,
viscosity, transport capacity, boundary shear stress and
flood power - - and both the spatial and temporal extent
to which the j6kulhlaup exhibits fluid, hyperconcentrated
or viscous debris flow conditions. The spatial extent of
flooding also depends on the nature of the flood routeway,
thereby also affecting the distribution of erosion and
deposition by flood waters, and the preservation potential
of these features.
Flow Characteristics
Magnitude, frequency and power of flows
The magnitude, frequency and power of j6kulhlaup
flows are directly reflected in the grain size, extent,
thickness and sedimentary structures of the resulting
deposits. In order to infer the palaeoenvironmental history
of the deposit, it is essential to improve understanding of
the control exerted by hydraulic conditions over the
resulting sedimentary record.
Peak flow magnitude depends largely on the volume of
water that has been stored and on the rate at which it can
drain through the glacial drainage system (Clague and
Mathews, 1973). Jrkulhlaup discharges commonly exceed 'normal' ablation-controlled flows by several orders
of magnitude. Modern examples come from Baffin Island
where Church (1972) recorded jrkulhlaup flows from
sudden lake drainage of ca 200 m 3 s -I, compared with
more normal flows of ca 20 m 3 s -l, while on the
Icelandic sandurs, increases of between 3 and 5 orders
of magnitude have been estimated for j6kulhlaups
generated by subglacial geothermal activity (e.g. Bj6rnsson, 1988; Maizels, 1991). Jrkulhlaups can therefore
contribute a significant proportion (e.g. 10-15%; see
Church, 1972; Russell, 1989) of the total annual meltwater runoff from a glacierised catchment.
Estimates of palaeohydraulic parameters for Pleistocene
and more recent jrkulhlaups have been based on a wide
range of numerical modelling techniques. Unfortunately, a
review of these methods is not within the scope of this
paper, but details may be found in Baker (1973a), Church
(1978), Costa (1983), Maizels (1983, 1987, 1989a),
Carling (1996b), and many others.
Some of the greatest flood magnitudes, powers and
boundary shear stresses estimated for j6kulhlaup flows
occurred at the end of the last glacial. Some of the largest
freshwater floods on Earth were those generated during
repeated Late Wisconsinan draining of glacial Lake
Missoula, in Washington State, which drained catastro-
795
phically through failure of its ice dam. Flood flows
reached peak discharges of 21×106 m 3 s -l, boundary
shear stresses of up to 104 N m 2 and stream powers as
much as 2.5x105W m -2 (Bretz, 1926; Baker, 1973a,
Baker, 1978; Baker and Bunker, 1985; Baker and Costa,
1987). Even larger floods appear to have occurred in the
Altay Mountains, Siberia, where Late Pleistocene lakes
were impounded behind tributary glaciers extending into
the Chuja valley (Baker et al., 1993; Rudoy and Baker,
1993; Carling, 1996a).
The nature of the j6kulhlaup hydrograph can also be
reflected directly in vertical variations within the
sedimentary profile. Jrkulhlaup hydrographs exhibit a
wide range of forms (e.g. Church, 1988; Costa, 1988b),
with rising and falling limbs extending over periods of
hours to months (e.g. Bjrrnsson, 1988). The flood
hydrograph is largely controlled by the mechanism of
flood generation (Fig. 1). In the case of lake drainage,
which is the most common source of jrkulhlaups,
flooding occurs through breaching of an ice dam, and
invasion of englacial or subglacial tunnels by meltwaters.
The flood hydrograph then becomes dependent on the
lake and dam characteristics and the rate of tunnel
expansion which, in simple situations, are amenable to
numerical modelling (Spring and Hutter, 1981; Clarke
and Mathews, 1981; Clarke, 1982; Clarke et al., 1984;
Craig, 1987).
A typical jrkulhlaup hydrograph exhibits a prolonged
rising limb and a rapid recession curve, reflecting the
gradual expansion of the tunnel routeway until the lake
basin has completely drained, or partially drained down to
the level of the tunnel inlets. For example, the drainage of
an ice-dammed lake on the western margin of the
Greenland ice-sheet produced a steady rising limb
extending over 18 hr before reaching a peak of
100 m 3 s l, and returning to pre-flood levels within only
12 hr (Russell, 1989; see Fig. 2A, B).
Many hydrographs also exhibit marked irregularities
during the course of the j6kulhlaup. During drainage from
an ice-dammed lake, ice tunnels can become temporarily
blocked by ice jams, which may partially or completely
shut off flood flows, until pressures rise sufficiently to
allow meltwater to break through. At Strandline Lake,
Alaska, for example, Sturm et al. (1987) recorded five
shut-offs of flow lasting over 40 hr. RCthlisberger and
Lang (1987) also demonstrate that highly irregular flood
hydrographs can be generated by extreme melt rates and
storm precipitation affecting Alpine glacier catchments.
Irregularities in j6kulhlaup discharge may also arise from
differential rates of expansion of the ice tunnel network,
from tapping of englacial or subglacial storages, or from
complex routing paths along the flood channelway.
Jrkulhlaups produced by different mechanisms are
characterised by distinct hydrograph forms. Thorarinsson
(1957), working in Iceland, for example, where jrkulhlaups occur in response to a wide range of mechanisms,
showed that while the hydrographs produced during
sudden drainage of ice-dammed lakes could extend over
periods of days and weeks, those produced from volcanoglacial events could reach peak flows of >105 m 3 s J in
796
Quaternar~, Science Reviews: Volume 16
(A)
(B)
FIG. 2. (A) Valley sandur at Kangerlussuaq, west Greenland, during normal summer ablation flows, looking downstream.
(Photo with permission of A. Russell.) (B) Same valley sandur during peak of j6kulhlaup flow in July 1987 at a discharge of
1080 m 3 s -1. (Photo with permission of of A. Russell.)
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
only 4-5 hr (Fig. 3A, B). Volcano-glacial jrkulhlaups
may also exhibit significant variations in flow during the
event, reflecting (permanent or temporary) damming of
flood routeways with lava or ash, or changes to the
subglacial volcanic topography.
Magnitude of sediment yields
Sediment concentrations in jrkulhlaups can be extremely high and can significantly affect the dynamics
and type of flow (see below), and hence the geomorphological impact of the flood. Suspended sediment concentrations recorded in jrkulhlaup events have reached as
much as 70,000 kg s - l (3.5% sediment concentration) in
an Icelandic jrkulhlaup flowing from a sediment-rich
volcanic catchment (e.g. Tomasson, 1974; Tomasson et
al., 1980) to only 4500 mg 1-1 from a Greenland
jrkulhlaup flowing in a sediment supply-limited, gneissic
channel (Russell, 1992). The high sediment concentrations of many jrkulhlaups reflect the normally abundant
sources of glacially-derived (and in some cases, volcanically-derived) sediment, which is introduced into highly
turbulent, powerful flows capable of transporting large
volumes of material.
Sediment inputs to jrkulhlaup flows are particularly
high in areas of rapid deglaciation (e.g. Hammer and
Smith, 1983), and where there are high influxes of
sediment from the valley sides or walls of the flood
routeway, or during volcanic eruptions. Sediment inputs
to the flood are also likely to be highest during the first
flood in a sequence, or when flood events are separated
by prolonged periods of time, allowing any depleted
supplies to be built up again before the next flood. High
sediment inputs may also be associated with periods of
high rainfall, snowmelt or slope instability in the
catchment (e.g. Gurnell, 1987).
Jrkulhlaups are capable of transporting a wide range of
sizes of material, ranging from silts and clays to large
boulders, in some cases reaching 10-15 m in diameter
(e.g. Baker, 1973a), as well as transporting numerous
large ice blocks over long distances, until they become
stranded on higher surfaces as flows begin to wane
(Fig. 3B, and see below).
Jrkulhlaup sediment transport normally accounts for a
very high proportion of the total sediment load removed
annually from the catchment. Church (1972) estimated
that jrkulhlaup flows removed up to 90% of total annual
sediment yields of a Baffin Island catchment, compared
with two outburst events removing ca 50% of annual
sediment yields in an Alpine catchment (Beecroft, 1983;
Gurnell, 1987).
Topographic controls on jrkulhlaup flows
The topographic nature of the flood routeway has a
major effect on the type of flow and resulting deposits
since it determines the zones of flow constriction,
expansion, separation and ponding, each controlling the
nature of the resulting depositional environment. Where
flow is confined between valley walls or within a rock-cut
channel, flow depths are considerably increased, leading
797
to a concomitant increase in shear stress, flood power,
transport and erosive capacities. By contrast, where flows
are able to expand on to unconfined sandur plains, flow
depths can decrease rapidly downstream, leading to a
dissipation of flood power and a reduction in erosive
impact. Where flows are temporarily impounded behind a
rock or moraine constriction, deeper quieter waters allow
upstream sedimentation, while the downstream flood
wave may be significantly attenuated, and peak flows and
suspended sediment loads reduced. This variety of
possible topographic conditions generates a wide range
of depositional environments, each one characterised by a
different kind of deposit. For example, point bars may
accumulate only in the bends of channels and bedrock
routeways, eddy bars at tributary mouths, pendant bars
downstream of obstacles, and expansion bars only where
flows open out from canyon or gorge sections on to plains
or broad valley floors (e.g. Baker, 1973a, 1984; Russell,
1992; O'Connor, 1993).
Pattern of deglaciation
The nature, rate and direction of deglaciation can have
an impact on the amounts of both water and sediment
released from the glacial system. Changes in the water
balance of the source ice mass affect the volumes and
rates of water release to the meltwater drainage system,
while fluctuations in the position of the ice margin can
control the drainage history of any ice-dammed lakes (e.g.
Teller, 1990; Maizels, 1997). Similarly, actively moving
and eroding ice generates larger volumes of transported
debris than stagnating ice, suggesting that maximum
sediment supplies to glacial meltwater systems are likely
to occur during periods of active ice advance. However,
during glacier retreat large volumes of glacial sediment
can be released and exposed to subaerial processes,
providing proglacial river systems with a virtually
unlimited sediment supply. Indeed, most sediment
transported by meltwater streams is derived not by direct
release from the ice into the channel but from reworking
of the channel boundaries (e.g. Hammer and Smith, 1983;
Fenn, 1987). Much j6kulhlaup sediment therefore appears
to be derived from reworking of earlier outwash deposits,
or from freshly exposed debris-rich ice, or, in the case of
volcanogenic floods, from fresh inputs of extruded
igneous material.
Large-scale vertical sedimentological trends within
interstadial or interglacial outwash deposits have been
widely interpreted as reflecting changes in meltwater
discharge associated with the advance or retreat of the ice
margin. For example, large-scale upward coarsening
sequences capped by till have been described from many
Quaternary deposits (e.g. Miall, 1980, Miall, 1983; Ehlers
and Grube, 1983), while large-scale upward-fining
sequences may also develop during ice retreat, in
response to increasingly distal flows, lower gradients
and downstream fining of outwash sediments. However,
both recessional and advance outwash sequences may
also exhibit the reverse vertical trend from that expected.
For example, a number of upward-fining outwash
798
Quaternary Science Reviews: Volume 16
(A)
(B)
FIG. 3. (A) Aerial view of Sula sandur, south Iceland, subject to j6kulhlaups from Vatnaj6kull, looking north to the ice cap
during peak meltwater flows. (B) Aerial view of Gigjukvisl, Skeidararsandur, south Iceland, during the waning stage of the
November 1996 j6kulhlaup. Note the dense accumulations of ice blocks on the expansion bar, and scattered ice blocks in the
channel. View is northeastwards towards Vatnaj6kull (see Russell et al., in prep.).
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
sequences are overlain by glacial till (e.g. Reed et al.,
1965; Vincent, 1984), while upward-coarsening or coarse
lag-capped outwash deposits have been recorded from
many retreat outwash deposits (e.g. Costello and Walker,
1972; Dawson and Gardiner, 1987). Such variations in
vertical grading reflect a wide range of local glaciobydrologic and channel processes, rather than changes in
runoff regime related solely to glacier fluctuations. The
role of high magnitude flood events is particularly critical
in the accumulation of long-term glaciofluvial sediment
sequences, since floods affect the degree to which earlier
flood and non-flood deposits are preserved in the
sequence. Most deglaciation vertical sediment sequences
are therefore likely to be more complex than those
suggested by traditional interpretations, since they
probably reflect numerous periods of aggradation and
erosion, multiple floods, and varying inputs of water from
different flow populations, and of sediment from different
sources (see discussion in Maizels, 1997). Most potential
for improved understanding of long-term sedimentological sequences lies in vertical facies modelling, where
sediment sequences can be related to changes in hydraulic
and sediment supply conditions (e.g. Maizels, 1993b,
1994).
FRAMEWORK FOR DESCRIPTION OF
JOKULHLAUP DEPOSITS
Classification of Outwash Types
Glacial outwash represents a particular form of alluvial
sedimentary environment, comprising humid-glacial fans,
coarse-grained braided and fine-grained low sinuosity
river systems in which water and sediment are largely
derived from a glacial source. Many of these glacial
environments are subject to both 'normal' and 'catastrophic' runoff events, the latter assuming variable
stratigraphic and geomorphic significance according to
rates of deposition and erosion, in turn reflecting the
runoff and sediment supply regimes, and the climatic and
tectonic settings. Unfortunately, at present there are
799
relatively few detailed examples of fans or outwash
deposits generated by j6kulhlaups.
Maizels (1991, 1993a) distinguished three dominant
outwash types, based on her analysis of sediment
sequences from the Icelandic sandurs. The classification
allows differentiation of outwash type according to the
nature of the dominant flood regime and sediment inputs
of the meltwater system (see Table 1).
Type I sandurs are 'classic' sandurs, defined as those
which are mainly produced by 'normal', ablation-related
seasonal meltwater flows, commonly operating within a
braided river environment, with no exceptional inputs of
sediment, and with regular reworking of proglacial
channel sediments. In proximal zones, sediment sequences
are dominated by clast-supported, massive, imbricated
gravels associated with the development and migration of
longitudinal bars (Miall's Gm lithofacies; and Trollheim
(Miall's 'GI') and Scott (Miall's 'GII') outwash types
(Miall, 1978; Rust, 1978). In more distal areas, linguoid
bars, overbank accretion and channel fill deposits lead to
the formation of sandy cross-bedded lithofacies (Miall's
Donjek (GIII), South Saskatchewan (SII) and Platte (SII)
braided river profiles)). Numerous studies of Type I
outwash have been carried out from both modern and
Pleistocene braided proglacial environments (e.g. Boothroyd and Ashley, 1975; Church and Gilbert, 1975; Miall,
1977, 1978; Boothroyd and Nummedal, 1978; Rust, 1978;
Smith, 1985; Brodzikowski and van Loon, 1991). These
will not be discussed any further in this paper.
Type II outwash is dominated by j6kulhlaup drainage
from ice-dammed or subglacial lakes, i.e. by 'limnoglacial' floods (Fig. 2A, B). These sandurs are characterised
by large-scale, coarse-grained bedforms, but no systematic
modelling or analysis of the universal diagnostic criteria
for identifying j6kulhlaup outwash has yet been completed. This paper goes some way towards these
objectives.
Type III outwash is dominated by 'volcano-glacial'
j6kulhlaup drainage, such as that which affects large areas
of the Icelandic sandurs (Fig. 3A, B), and that generates
distinctive suites of lithofacies sequences. These are
discussed in more detail below.
TABLE 1. Dominant lithofacies sequence of three characteristic outwash types (after Maizels, 1991, 1993a)
Sandur or
outwash
type
Dominant lithofacies
sequence
Secondary lithofacies
sequence
Dominant lithofacies
types
Type I
A4
A, G
Gmi, Sh, Suf, Sr,
St, Guf, FI
Type II
B2
B, C, E, F
Guc, Guf, Gxp,
Gxt, Blg
Type Ill
E4
E3, C, D1-D5, El,
E2, F, G, H
GRIn, GRx, GRh,
Gm, Gx, Gh, Sm,
Suc, Guc
See Table 2 and Table 3 for keys to lithofacies sequences and types.
Secondary lithofacies
Dominant meltwater
types
regime and depositional
environment
Gm, Sp, Gp, Gt, Sd,
Fd, Fe, Fro, Fs
Normal seasonal
meltwater flows in
braided fiver
environment
Gh, Sh, Suf, Go, St, Sp, J6kulhlaup drainage
Gh, F1
from ice-dammed or
subglacial lake ('limnoglacial' floods)
Guf, Suf, Gt, Gp, St, Sp, J6kulhlaup drainage
Sh, FI, GRch, GRo,
during subglacial
GRni, GRd, GRuc,
volcanic eruption
GRmb, GRmp, GRmc,
('volcano-glacial'
Go, Bm
floods)
800
Quaternary Science Reviews: Volume 16
TABLE 2. The main lithofacies types characteristic of j6kulhlaup and non-j6kulhlaup outwash (after Maizels, 1991, 1993a)
Boulders (>256 mm)
Bi
Blg
Bm
Bx
Bsl
Gravels (8-256 mm)
Gh
Gm
Gmi
Gni
Go
Gp
Gs
Gsi
Gt
Gu
Guc
Guf
Gxp
Gxt
Granules (2--8 ram)
GRch
GRd
GRm
GRmb
GRmc
GRmp
GRo
GRruc
GRruf
GRt
GRuc
GRuf
GRx
Sands (0.06~3--2 mm)
Sd
Sh
Sm
Sp
Sr
St
Suc
Suf
Sx
Fines (<0.063 mm)
Fd
FI
Fm
Fs
Fe
Lithofacies Types and Lithofacies Profiles
Using Miall's framework of lithofacies description,
modified by Maizels (1991, 1993a), five main lithofacies types can be recognised from j6kulhlaup deposits
according to dominant grain size: boulder beds (B);
Imbricated boulders
Boulder lag
Massive boulder bed
Large-scale boulder cross-bedding
Single lithology boulder deposit
Horizontally bedded gravels
Massive, clast-supported crudely bedded gravels
Massive clast-supported, imbricated gravels
Normal-inversely graded gravels
Openwork gravels
Small-scale planar cross-bedded gravels
Matrix-supported gravels
Matrix-supported, imbricated gravels
Small-scale trough cross-bedded gravels
Matrix-supported, unsorted gravels
Upward-coarsening gravels
Upward-fining gravels
Large-scale planar cross-bedded gravels
Large-scale trough cross-bedded gravels
Channelled massive granules
Deformed granule bedding
Massive, homogeneous granules
Massive, pseudo-bedded
Massive, with isolated clasts
Massive, with pebble stringers
Openwork granules
Repeated upward-coarsening cycles
Repeated upward-fining cycles
Trough cross-bedded granules
Upward-coarsening granules
Upward-fining granules
Cross-bedded granules
Deformed sands
Horizontal/plane-bedded sands
Massive sands
Plane cross-bedded sands
Ripple cross-laminated sands
Trough cross-bedded sands
Upward-coarsening sands
Upward-fining sands
Cross-bedded sands
Deformed laminated silts and clays
Laminated silts and clays
Massive silts and clays, or silts
Silts and clays with load structures
Laminated silts and clays with erratic dropstones
gravels (G); granules (GR); sands (S); and, fines (F).
The main sedimentary structures associated with each
lithofacies type are summarised in Table 2 (see Maizels,
1991, 1993a for more detailed discussion).
Maizels differentiated flow environments within the
Icelandic sandurs according to the sedimentary character-
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
801
TABLE 3. Classification of lithofacies types and sequences in j6kulhlaup outwash deposits (modified from Maizels, 1991, 1993a)
Lithofacies Characteristic structures
sequence
Dominant
lithofacies
types
Secondary
lithofacies
types
Examples
Outwash type
Location
II A3 A4
Missoula
floods
Reference
Classification in
Maizels, 1991,
Maizels, 1993a
Stratified
A
Al
A2
A3
A4
BI
Horizontally laminated/ Gmi, Sh, Suf, Gm, Guf, St, Sp,
bedded, intercalated
F1
Gp, Gt, Sr, Sd,
with small-scale crossFm, Fs, Fd, Fe
bedding, clast-supported
sands and gravels
Upward-fining
Upward-coarsening
Cyclic-normal grading
Cyclic-normal grading
with coarse interbeds
and coarse lag deposits
Large-scale crossbedded gravels and
boulders
Large-scale crossbedding
II A4
IlI A3
II BI
Gxp, Gxt, Blg
Suf, Go
II B1
Baker, 1973a, b;
Waitt, 1980,
1984, 1985;
Atwater, 1984,
1986
Chuja and
Rudoy and
Kuray basins, Baker, 1993
Siberia
Myrdalssandur, Maizels, 1993a
Iceland
Kuray dunes,
Siberia
Carling, 1996a
Rocky
Clague, 1975
Mountain
Trench
Lake Bonneville Malde, 1968;
flood
Jarrett and
Malde, 1987;
O'Connor, 1993
Missoula floods Baker, 1984
B2
Large-scale crossGxp, Gxt, Gxuf,
bedding with coarse lag
Gxuc
Bx
II B2
B3
Upward-fining largeGxp, Gxt, Gxuf
scale cross-bedding
Upward-coarsening
Gxp, Gxt, Gxuc
large-scale crossbedding
As B3, with coarse lag Gxp, Gxt, Gxuf,
Blg
As B4, with coarse lag Gxp, Gxt, Gxuc,
Blg
St, Sp, Suc
II B2
Bx, Gh
II B2
Platovo dunes, Carling, 1996a
Siberia
Bx, Gh
II B2
Bx, Gh
II B3
West Greenland Russell, 1992
and in prep.
Tippecanoe fan, Fraser and
Wabash valley Bleuer, 1988
Go
II C 1
B4
B5
B6
C
C1
C2
Boulder deposits
Large-scale, crudely
horizontally bedded
boulder deposits
Gravel and boulder
accumulations with
boulder lag
Bi, Blg, Bsl, Bhl
Gh
CI, C2, G
Porcupine
Thorson and
valley, Yukon/ Dixon, 1983;
Alaska
Thorson, 1989
F
Massive
D
Massive graded
sediments, matrix-poor
D1
D2
D3
D4
D5
Normal grading
Cyclic normal
Normal-inverse
Inverse
Inverse-normal
III D
Icelandic
sandurs
Maizels, 1989a,
b, 1991, 1992,
1993a
C
Gmi, GRuf, Suf
Sh, F1
Gmi, GRuf, Suf
Sh, F1
Suc, GRuc, Gmi
Gmi, Suf, GRuc
Sh, FI
Guf; GRuc, Gmi Gh, GRh, Suf,
Suc, GRo
istics o f successive vertical lithofacies profiles. A
modified classification system is adopted here (summarised in Table 3) with a view to presenting a model o f
diagnostic j6kulhlaup profiles at the end o f the paper.
Eight types of vertical lithofacies profile have been
distinguished: Types A to C represent stratified j6kulhlaup sediment profiles, while Types D to G represent
profiles dominated by structureless, massive deposits with
varying associations with stratified sediment. Type H
represents sediments which have been subjected to
structural deformation.
Flow Types and Lithofacies Sequences
The relationships between hydraulic conditions and
fluvial lithofacies types are relatively well established,
Quaterna#:v Science Reviews: Volume 16
802
TABLE 3. continued.
Lithofacies Characteristic structures
sequence
Dominant
lithofacies
types
Secondary
lithofacies
types
Massive homogeneous,
with bedding at top and/
or base
E1
E2
E3
E4
F
FI
Massive, with crossGRIn, GRx,
bedding at the top
GRt, Gxp, Gxt
Massive with horizontal GRIn, GRh,
bedding at the top
Gin, Guf, Suf
Massive with crossGRin, GRx.
bedding near top,
Gxp, GRt,
capped with horizontal
GRh
bedding
Massive with basal
GRh, Gm,
gravels
Gh, GRm.
and capping of crossGRx, GRt,
bedded
GRo
and horizontally bedded
units
Examples
Outwash type
Souris spillway Kehew, 1982:
Kehew and
Lord, 1986,
1987: Kchew
and Clayton.
1983
Go, Sh, F1. Fs
11 E2
Wabash valley
GRch, GRo, Sh.
F1, Fs
111 El-3
Icelandic
sandurs
GRch, Sh, Gs.
FI, Fs, Big, Gxp,
Gxt
Ill E4
Myrdalssandur, Maizels, 1991,
South Iceland
t993a
I11 FI-F4
South Icelandic Maizels, 1989a,
sandurs
b, 1991, 1992,
1993a
Mid-continental Kehew. 1982;
spillway
Kehew and
channels,
Lord, 1986,
North America 1987; Kehew
and Clayton,
1983
GRch, Big, GRo
Massive, poorly
structured/no bedding
structures, matrix-poor
[Indistinct beddingl
F3
F4
F5
Decreased amount o1
internal
bedding
[No bedding]
Massive poorly
structured with coarse
lag
G
Massive, structureless,
matrix-rich
H
Deformed bedding
Reference
IEI
II F5
Sm
F2
Location
Classification in
Maizels, 1991,
Maizels, 1993a
GRIn, Gin
Bm
Oms
Blg
II F5
Fraser and
Bleuer, 1988
Maizels, 1989a,
1989b. 1991,
1992, 1993a
A
Baldakatj delta, Elfstr6m, 1983,
N. Sweden
1987, 1988
Gs, Gu, Dms
Gsi
111 G
Icelandic
sandurs
Maizels, 1989a,
b, 1991, 1992,
1993 a
E
GRd, Sd
Fs, Gs, Gu
I11 H
Icelandic
sandurs
Maizels, 1989a,
b, 1991, 1992,
1993 a
D
especially for sand bedforms. However, the hydraulic
conditions associated with deposition from deep, fast,
highly turbulent floods, especially those containing
relatively high sediment concentrations and transporting
large boulders, are more poorly understood. In addition,
the terminology is often confused, and largely derived
from non-glacial environments.
Most j6kulhlaup flows are highly turbulent, with
sediment concentrations well below the threshold of
40% for heavy sediment suspensions or 'hyperconcentrated' grain flows. The initial stages of a j6kulhlaup may
be characterised by sediment-laden flows in which
concentrations exceed ca 80%, resulting in non-Newtonian
debris or mud flows (Costa, 1984, 1988a, b; Smith, 1986).
High sediment concentrations act to d a m p e n flow
turbulence, and increase the bulk density and yield
strength of the flow. These theologic changes allow
hyperconcentrated and debris flows to transport not only
large amounts of sediment, but also to transport large
boulders and ice blocks through the effects of buoyancy
and dispersive stresses. The different flow types produce
distinctive landform and sediment assemblages.
Turbulent fluid flows
Flows with low sediment concentrations (normally
<40% by weight, <20% by volume) generally exhibit
turbulent characteristics, allowing the development of
stratified bedforms associated with the downstream
migration of tractive load, grain-by-grain movement.
These processes can produce a range of sedimentary
structures associated with turbulent fluid flow, in which
J. Maizels: J6kulhlaup Deposits in Pvoglacial Areas
T3
__
T4
T5
0
100
200
!
!
i
T1
Magnetic
T6
m
803
north
T2
GR
Stage
recorder
TI~
~
T3
T2
ss Mega-ripples
T5
T6
!;i:i; Exhumed terrace e Vegetation //// Pond bi
Slope breaks ~
~
Normalflows
~ Obstaclemarks ~
Activechannels
Chutechannels
FIG. 4. Morphological map of 'Sandur l', Kangerlussuaq, west Greenland, illustrating the main zones of deposition and
scour in response to repeated limno-glacial j6kulhlaups of ca 1080 m~ s i (from Russell, submitted).
fluid shear induced by the boundary varies logarithmically through the vertical profile. At subcritical Froude
numbers (FR<I), the bedform sequence with increasing
depth or velocity ranges from plane-bedded fine sands to
ripples and dunes, to 'megaripples' and sand waves (see
below) in deep, high velocity flows. At supercritical
Froude numbers (FR>I) dunes become washed out to
form plane-bedded coarse sands, and imbricated gravel,
pebble and cobble sheets. J6kulhlaup flows, although
characterised by extremely high discharges, often remain
subcritical, reaching supercritical conditions only locally
in constricted bedrock reaches and along steep sections of
the channel.
Macroturbulent flow conditions
Macroturbulent flow conditions arise during very deep,
high gradient flows which can lead to the development of
secondary circulation, Flow separation, and the growth
and collapse of vortices around obstacles and in the shear
zone along irregular channel boundaries, especially largescale dunes (Matthes, 1947; Baker, 1973a, 1984). Matthes
(1947) defined large-scale turbulent structures as 'kolks'.
The upward vortex activity is characterised by intense
energy dissipation and steep pressure and velocity
gradients, acting to generate extremely powerful hydraulic lift forces. Although macroturbulence is still not fully
understood, it is clear that it can lead to the transport of
boulders in suspension. The resulting deposits include a
variety of boulder deposits, including boulder levees and
berms along former shear zones, such as channel margins.
(Bingham) or high viscosity, non-Newtonian (pseudoplastic) behaviour. Lower viscosity flows may form a
highly concentrated, cohesionless grain flow (e.g. Fisher,
1971; Nemec and Steel, 1984). In hyperconcentrated (or
hyperpycnal) flows, with 40-70% sediment concentration
by weight (20-47% by volume), and bulk densities of
between 1.01 and 1.3 g cm 3 (Costa, 1984), boundary
shear can be transmitted through the fluid-sediment mix
as a dispersive pressure, such that inter-grain collisions
cause the coarser grains to move to zones of lower shear,
i.e. to the edges of the flow. This mechanism can promote
inverse grading of sediments, with larger clasts found as
'rafted' surface and lobe-edge boulders and as isolated,
outsized clasts, and absence of cross-stratification (e.g.
Pierson, 1981; Lajoie, 1984; Postma, 1986; Smith, 1986).
Sediments deposited by hyperconcentrated flows tend to
be more poorly sorted than water flood sediments (Trask
sorting coefficients of 1,0 to 1.6, compared with 1.8 to
2.7, respectively; Costa, 1984). Openwork gravel sequences can also develop, especially on foreset slopes,
where high energy traction currents prevent the deposition of fines and deposit short lenses of matrix-free
granules or gravels. Where flows are more turbulent,
shearing may produce crude sub-parallel laminations, a
crude fabric, imbricated clasts, and basal erosional scours
and flutes. Deposits may form extensive sheets across the
whole sandur plain (Maizels, 1993a), but with increasing
sediment concentrations and flow cohesiveness deposits
may form steep fans, lobes or plugs (Lawson, 1982;
Maizels, 1989a).
Debris flows
Hyperconcentrated flows
Once the yield strength has been exceeded, laminar
flows may assume either low viscosity, Newtonian
The terminology used to describe debris flows is
tortuous, and largely derived from non-glacial environments. Here, debris flows are defined as those containing
804
Quaternao, Science Reviews: Volume 16
A
I
I
14
21
(m)
01
(b)
(a)
(d)
(c)
S~p
-0.50 !
Sp(pe)
?
-0.751
(m)
(e)
Gm
.0.25 I
~
Sp 262 °
-1.00
35°dip 268 °
-1.25
25°dip 239 °
-1.50
25°dip 275 °
20°dip 264 °
p(pe)
,~30°dip 331 o
Sp 25Odip 305°
Sp(Pe)
~,-~.
~Sp
25°dip 300 °
Sp
-1.75
-2.00
30/35°dip 312 °
25Odip 300 °
~
Sp(pe)
~,~
35°dip 318 o
Sp(Pe) 30°dip 10 °
7°dip 354 °
Sp 5°dip 228 °
-2.25
(a)
(b)
(c)
(d)
(e)
0
0.25
Sh
$h
0,50
Gm
(m) 0.75
Pe)
~_~
20°dip 230 °
-.
Gm
Sp/ep " ' "
~ p: l ~ 0~ O d- i
280 °
1.00
1.25
Magnetic bearing
1.50
5
14
19
25
(m)
FIG. 5. Vertical sedimentary profiles of sections on 'Bar M' of 'Sandur l', Kangerlussuaq, west Greenland, in response to
repeated limno-glacial j/Skulhlaups of ca 1080 m3 s-~. See Fig. 4 for location of Bar M. (A) Proximal edge of distal limnoglacial bar, (B) Mid-bar location between several chute channels (from Russell, submitted).
sediment concentrations of between 70 and 90% by weight
(ca 47-90% by volume), possess bulk densities of 1.82.3 g cm -3, and exhibit non-Newtonian behaviour (Costa,
1984). Water and sediment move at the same velocity,
following the Coulomb-viscous model, in which particles
are supported primarily by sediment cohesion and buoyant
forces, as well as dispersive stresses and structural support
from intergrain contacts. All sediment sizes may be
present, resulting in a very poorly sorted deposit (sorting
coefficients of between 3.6 and 12.3). On flow cessation,
debris flows may 'freeze' en masse to produce massive,
poorly sorted, structureless, non-graded, matrix-supported
deposits. Such highly viscous, cohesive sediments
commonly form distinct lobate forms, with lobe height,
morphology and maximum clast sizes related to strength of
the debris, bedslope, and grain concentration (Johnson,
1970; Costa, 1984; Nemec and Steel, 1984). Debris flows
require relatively high gradients (e,g. 0.045-0.310; Costa,
1984) to sustain motion, and hence occur only locally in
proglacial areas, normally confined to ice-proximal sites
and decaying rapidly downstream to form distal flood
regime fluvial deposits (e.g. Lawson, 1982; see below).
Composite .flows
A single flood event may well exhibit a range of flow
conditions, and hence produce a range of associated
depositional sequences that vary both spatially and
temporally. Common temporal changes include the
occurrence of fluid 'intersurge' flows (e.g. Pierson,
1981) in which fluid bedforms alternate with more
massive or inversely graded, coarse elastic sediments
deposited by the main flood 'surge'. A surge is defined
here as a turbulent, hyperconcentrated flow in which
sediment and fluid move en masse. The 'freezing' of
sediments as water and/or sediment supply diminish can
result in reverse grading, rafted isolated large clasts, and
laminations due to late-stage shearing during deposition
(Carter, 1975; Postma, 1986). J6kulhlaups may also
comprise pre-surge, surge and post-surge stages, with
J. Maizels: JSkulhlaup Deposits in Proglacial Areas
the main flood surge characterised by hyperconcentrated
flows, with watery flows occurring in the early and late
stages of the flood (e.g. Harrison and Fritz, 1982; Pierson
and Scott, 1985, 1988a, b; Maizels, 1991, 1993a). Rapid
deposition of debris flow sediments releases excess water
from a breakout point, leading to transformation downstream into hyperconcentrated streamflow or fluid deposits
(e.g. Lawson, 1982). Dewatering of proximal hyperconcentrated flow deposits can also lead to distal incision of
outwash by fluvial 'runout' flows.
MORPHOLOGY AND SEDIMENTOLOGY OF
J()KULHLAUP DEPOSITS
Major DepositionalLandforms
The largest depositional landforms that may be
produced by jrkulhlaups include outwash fans, valley
sandurs and sandur plains. The coastal plains of southern
Iceland (Fig. 3A, B), parts of southwestern Alaska, and
western Greenland (Fig. 2A, B) and Baffin Island, for
example, contain some of the most extensive sandurs and
valley sandurs and many, if not all, are subject to periodic
jrkulhlaup events generated by a range of different
mechanisms (e.g. Church, 1972; Fahnestock and Bradley,
1973; Boothroyd and Ashley, 1975; Maizels, 1991;
Russell, 1992). Pleistocene outwash plains were more
extensive and bounded the margins of many segments of
the Laurentide and Eurasian ice sheets, where icedammed lake drainage was often catastrophic (e.g.
Kehew and Lord, 1987). Jrkulhlaup landscapes exhibit
a wide variety of large-scale erosional forms as well as
depositional features, such as the hundreds of streamlined, residual hills, longitudinal grooves and giant
potholes, scours and plunge pools that characterise the
Channelled Scablands of the Columbia Plateau, Washington State (Baker, 1973a, Baker, 1973b), and the
complex systems of huge spillway channels that lead
away from all the major glacial lake basins bounding the
southern edge of the Laurentide Ice Sheet (e.g. Kehew
and Lord, 1987). The main depositional zones contain a
range of macro bedforms (bars) and meso bedforms
(dunes), as well as 'washed' sandur spreads and boulder
lags; pitted or kettled outwash and fields of ice-block
obstacle marks; steep, lobate and hummocky proximal
fans; and a variety of distinctive sediment assemblages
(see summary in Maizels, 1995).
Macroscale Bedforms: Bar Forms
The terminology used to describe bars is confusing and
ambiguous, especially since bars may be depositional or
erosional in origin, and reflect formation during a single
flood event or reworking during numerous flow events.
The terminology used here follows that adopted by Baker
(1973a) for the Missoula flood deposits.
The medium-scale depositional landforms associated
with jrkulhlaup outwash include expansion bars, pendant bars (downstream of bedrock obstacles), point bars
and eddy bars, as well as streamlined erosional bars.
805
Each bar type is characterised by distinctive sediment
associations.
Expansion bars are associated with deposition in areas
of flow deceleration, especially at the junction between
steep, confined reaches and wide, low gradient reaches.
Many large bars have been used as indicators ofjrkulhlaup
outwash, while large-scale cross-bedding has been
interpreted as representing the foreset bedding of
migrating bar forms (e.g. Allen, 1982). Expansion bars
formed the largest type of bar deposit generated by the
Lake Bonneville flood which drained along the Snake
River course (Malde, 1968; O'Connor, 1993). The bars are
up to 5 km long, and exhibit steep foresets (lithofacies
Gxp; see Table 2) and trough and fill structures (Gxt)
capped by up to 3 m of horizontally bedded winnowed,
armoured, imbricated boulders up to 4 m in diameter
(Blg), forming a distinctive 'B2' lithofacies sequence
(Table 3). Longitudinal bars, also located downstream of
constrictions, were found to extend for some 3 km parallel
with the main channel. Downstream of 'Mile 460' gravel
bars are littered with boulders up to 3 m in diameter, and
reach up to 90 m in height (Jarrett and Malde, 1987).
The internal stratigraphy of bar deposits that accumulated during the Bonneville Flood also reflects deposition at different stages of the jrkulhlaup, namely,
during the main flood peak followed by waning stage
aggradation. O'Connor (1993) describes bar deposits
from parts of the flood routeway which exhibit largescale foresets (Gx), with individual sets 0.25-1.5 m
thick, and trough-and-fill structures (Gxt) tens of metres
wide. This unit is overlain by 1-3 m of coarser-grained
but better sorted, horizontally bedded gravels containing
imbricated boulders up to 10 m in diameter, forming
a Type B2 vertical profile (Table 3). This sequence
was interpreted by O'Connor (1993) as representing
rapid downstream accretion of large-scale bar fronts
during the main highly turbulent flood wave, followed
by rolling and winnowing of bar top material to form
an armoured surface of imbricated cobbles and boulders
during recession flow.
Type B2 profiles have also been described from
expansion and point bars on a west Greenland valley
sandur subject to repeated j6kulhlaup events. The bars are
composed of large-scale sand and gravel cross-bedded
units overlain by coarse cobble-boulder lag (Fig. 2A, B,
Figures 4-6; and see Russell, 1992, and Russell,
submitted). The sequence was attributed to the downstream migration of gravel bars during peak flows,
followed by high energy sheet flows which initiated
winnowing of the bar surface to create a coarse cobbleboulder lag.
Pendant bars are deposited in zones of localised flow
expansion or deceleration, particularly downstream of
obstacles which lie within the main flow path. Large
scale pendant bars have been identified in uniform steep
gradient channels of the Washington scablands drained
by the Missoula floods. Here, pendant bars are up to
3.2 km long and extend up to 30 m above the valley
floor (Baker, 1973a). Similarly, along the route followed by the Lake Bonneville flood in Idaho, narrow
806
Quaternao, Science Reviews: Volume 16
FIG. 6. Large-scale, imbricated boulder deposits forming a point bar along a j6kulhlaup routeway at the edge of the west
Greenland ice sheet, and associated with j6kulhlaup discharges of ca 1080 m 3 s 1. Material is derived from erosion of
gneissose bedrock from a gorge section lying a short distance upstream (see also Russell, 1992: Russell, submitted). Flow
was from right to left.
steep crested pendant bars up to 2 km long, bounded
by deep scour troughs, were identified by O'Connor
(1993).
Eddy bars are formed at the mouth of tributary valleys
where backwater eddies are created in the tributary flow,
leading to deposition of sediments derived from two
different sources: from tributary flow and from marginal
flow in the main channel. Eddy bars contain a wide
variety of sediment sizes and structures, with interfingering between poorly sorted boulder gravels, cross-bedded
granule gravels, graded sand-silt layers and laminated
silts. The foresets indicate a range of flow directions, for,
while most foresets dip away from the main channel
(especially when deposited by j6kulhlaup flows), others
dip towards the main channel, reflecting fluctuations in
backwater flows, eddies and back-flow currents (Baker,
1984). Eddy bars can extend upstream to form sequences
of slack-water deposits (see below).
In addition, streamlined boulder bars can also be
formed by erosion of earlier outwash deposits during
waning stage j6kulhlaup flows. On Myrdalssandur, for
example, bars up to 4 km long and mantled with a variety
of kettle forms, were formed by waning stage erosion into
sheet deposits covering the whole sandur (Fig. 7: Maizels,
1992, 1993a).
Meso-scale Bedforms: Giant Dunes
The most distinctive large-scale bedforms that are
produced during catastrophic j6kulhlaup drainage are
large-scale dunes. No standard terminology has been
adopted for these features, and they are also known by a
variety of terms including giant 'current ripples', °meg>
ripples', 'whaleback dunes' or 'gravel waves'. The scale
of these features is largely dependent on flow depth and
size of material available for entrainment.
Giant dunes formed in zones of flow expansion during
catastrophic drainage of Lake Missoula, where over 100
'giant ripple' trains have been identified, most of them
concentrated on proximal ends of riffles (Pardee, 1942;
Baker, 1973a, b, 1984). The dunes exhibit huge gravel
foreset beds comprising alternating beds of granules,
gravels and pebbles, with the stoss slopes mantled with an
armour of cobbles and boulders up to 1.5 m diameter (a
Type B2 profile: Table 3). The ripples exhibit heights and
wavelengths of ca 15 m and 150 in, respectively, and
were associated with maxirnum j6kulhlaup velocities
e x c e e d i n g 30 m s l and d i s c h a r g e s o f n e a r l y
14x10 ~ m 3 s 1; Baker, 1973a, b, 1984: Craig, 1987),
Large-scale dunes have also recently been identified as
the result of cataclysmic j6kulhlaup drainage during
failure of an ice dam in the Chuja River valley in the
Altay Mountains, Siberia (Baker et al., 1993: Rudoy and
Baker, 1993). Carling (1996a) has studied the morphology, sedimentology and palaeohydraulic implications of
six major dunefields in the Chuja valley, the largest (the
Kuray dunefield) extending over a 24 km tract. According to Carling, the dunes comprise unimodal, openwork,
coarse gravel locally filled with small amounts of sand or
granule matrix. Median b-axis particle sizes average
35 mm, while cobbles and boulders up to 0.5 in diameter
are common. In addition, large tabular blocks over 2 m in
diameter occur on the stoss or crests, either as isolated
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
i~
' i
807
¸ ~¸
FIG. 7. Hummocky surface of erosional bar on volcano-glacial outwash, Myrdalssandur, south Iceland. The j6kulhlaup
occurred in 1918 AD, and generated hyperconcentrated flows up t o l 0 6 m 3 s ~. The bar is mantled with gravel dunes,
'rimmed kettles' and 'till-fill' kettles. Flow was from right to left. Note Katla ice cap in background, and Land Rover for
scale.
blocks or in clusters, surrounded by horseshoe scour
hollows.
Giant dunes have also been identified on the bars and
flood terraces produced by j6kulhlaups from Neoglacial
Lake Alsek, Yukon (Clague and Rampton, 1982). The
lunate and long-crested dunes are composed of pebble,
cobble and boulder sized material. They exhibit wavelengths up to 200 m long, and heights of >5 m, while
erratic boulders were found to have been rafted in ice
blocks for many kilometres downstream. Smaller scale
'megaripples', up to 0.5 m high and 10.5 m wavelength,
are found on Solheimasandur in southern Iceland,
associated with volcano-glacial j6kulhlaup discharges of
c a 10 4 m 3 s J(Fig. 8; cf. Fig. 7; Maizels, 1989a, b).
Sediment sequences containing large-scale crossbedded structures related to an extreme flood event have
been described by Fraser and Bleuer (1988) from the Late
Wisconsinan Wabash valley in Indiana, which carried
meltwater drainage from the Lake Erie basin. These
sequences correspond to Type B3 profiles. At the
Tippecanoe Fan, where meltwater that had been stored
in disintegrating ice to the north was rapidly released, the
sequence comprises (1) basal cobble gravels exhibiting
crude horizontal bedding and grading up into crossbedded sands and gravels, overlain by (2) a boulder lag
and (3) a series of troughs infilled with an upward
coarsening and thickening sequence of successive sets of
climbing ripples, plane beds, festoon trough sets, through
to pebbles and cobbles (St, Suc, Guc, Gt, Gh). The main
part of the sequence comprises up to 30 m of large-scale
cross-bedded cobble gravels forming megasets up to 5 m
thick (Gxp) (unit 4) (Fig. 9), generally exhibiting normal
grading within each set. The basal sands and gravels (unit
1) were interpreted as pre-flood braided outwash
associated with formation of longitudinal and transverse
bars (Type A1 profile). By contrast, the cross-bedded
gravels (unit 4) were considered to represent large-scale
equilibrium bedforms, exhibiting tangential basal contacts, in turn associated with the rapid accretion of 3dimensional dunes, with gravel transported in at least
intermittent suspension past the point of flow separation.
Fraser and Bleuer (1988) argue that the discrete upward
coarsening and thickening of the trough infill sediments
(unit 3) at the base of the flood gravels would have
required several days of slowly increasing flow depth,
velocity and sediment availability before reaching the
flood peak, which generated the main large-scale dune
systems. The j6kulhlaup is likely to have declined rapidly
from flood peak since set thickness declines upward,
reflecting lower flow depths and sediment fluxes as the
channel aggraded. The absence of a significant decline in
grain size upwards reveals that flow velocities remained
fairly constant until waning stage flows, when some local
reworking took place to produce fine-grained trough
cross-sets at the top of the sequence. Elsewhere, sand
content increases upwards. The full sequence therefore
resembles a Type AI profile (unit 1) overlain by a Type
B3 profile (see Table 3), in which the characteristics of
both the rising and falling limbs of the flood hydrograph
could be inferred from variations in the grain size and
scale of sedimentary structures through the vertical
profile.
808
Quaternary Science Reviews: Volume 16
FIG. 8. Pumice granule 'mega-ripples' on the slopes of a glacio-volcanic j6kulhlaup channel, Skogasandur fan, south
Iceland. The flood occurred ca 1500 BP, reaching a peak discharge of ca 8000 m3 s l (Maizels, 1989a). Flow was from left
to right in the picture.
Slack-water Deposits
Where a tributary valley lies at a high angle to the main
flood channel, the valley can act as a sediment trap during
backwater flooding to produce distinctive sediment suites
known as 'slack-water sediments' (Baker, 1973a, 1983;
Patton et al., 1979) or 'backflood deposits' (Atwater,
1984). These sediments can form upstream extensions of
eddy bar deposits or merge with glaciolacustrine facies
where the main valley remains ponded for long periods of
time. The elevations of successive flood deposits within
slack-water sequences have been widely used in reconstruction of the hydraulic gradient and palaeodischarges
of associated j6kulhlaups (e.g. see methodology in
Kochel and Baker, 1988; Baker et al., 1983; O'Connor
and Webb, 1988).
The most detailed analyses of slack-water deposits
have been undertaken in tributary valleys of glacial Lake
Columbia, which formed the main receiving basin of
floods from glacial Lake Missoula during successive
Pleistocene glaciations, and particularly during the last
glacial phase from ca 15.5 to 13.35 ka BP (Baker and
Bunker, 1985; Waitt, 1985). Atwater (1984), Atwater
(1986) identifies two types of slack-water deposit from
the Sanpoil tributary: slack-water rhythmites or varves
(Type A3 profiles; Table 3) and flood beds (Type A4
profiles; also named 'Touchet Beds'). The slack-water
rhythmites are composed of laminated silt and clay
couplets, 1-2 cm thick, which exhibit internal normal
grading from basal very fine sand to silt. The rhythmites
are interbedded with flood beds, 10-20 cm thick, which
also exhibit clear upward fining grading. In proximal
zones, the basal horizon comprises graded structureless
gravel, overlain successively by horizontally laminated
very coarse to medium sand; ripple cross-laminated and
climbing ripple cross-laminated coarse to fine sand; and
parallel or horizontally laminated very fine sand and silt.
There is some evidence of load casting, deformation and
slumping, and ice-rafted glacial erratics. This sequence
closely resembles a typical Bouma sequence deposited by
a marine turbidite, suggesting that these slack-water
sediments represent rapid deposition from dense sediment
gravity flows during flood surges up the backwater
tributary valleys. A distinctive feature of these flood beds
is that they become finer grained and thinner upvalley,
with cross-beds dipping upvalley, reflecting the direction
of flood surges away from the main channel (Baker,
1973a, b; Patton et al., 1979; Baker and Bunker, 1985).
The interpretation of slack-water deposits is not
straightforward, however, since rhythmites may not
necessarily represent a single flood event. Many j6kulhlaups exhibit multiple peaks and the irregularities of the
flood routeway can act to modify successive flood waves
to produce a highly complex hydrograph, such that a
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
Graphic
log
Interpretation
Percent
14
O 0
O~
3 0
O0
C
12
Boulder Deposits
composition
50
lO0
°..."'.
°0 * o . . . . .
e°'.'l
'..
* , ' =m ' .
@
° 0
'.
0 0 °l" *" • ".' •
0 0 * P, ° '''
Explanation
Cobbles
F o o d deposits
formed under
conditions
Coarse pebbles
of deep,
powerful flow
Fine pebbles
10
Granules
) 0 , e l " • .'. ".
0
• • Q. •
Sand
Silt and clay
O u t w a s h - fan deposits
formed under
6
conditions
of episodic flow
in a proximal
ice setting
V a l l e y - train d e p o s i t s
2
~
809
formed under
conditions
of episodic flow
in a distal setting
FIG. 9. Stratigraphic sequence at Attica, Indiana, showing
internal structures and grain-size distribution of j6kulhlaup
deposits and underlying valley-train and outwash-fan sediments
resulting from rapid drainage of water stored in the disintegrating Laurentide ice margin to the north (from Fraser and Bleuer,
1988).
single lake drainage event may be represented in the
sedimentary record by more than one rhythmite horizon
(Baker, 1973a; Baker and Bunker, 1985; Maizels, 1997).
Nevertheless, making assumptions about the frequency of
varve formation and flood bed occurrence allowed Waitt
(1985) to suggest that over 40 floods occurred during the
last glacial phase, i.e. about every 20 to 60 years over a
3000-4000 year period, but with flood frequency
increasing towards the end of glaciation as the ice sheet
thinned. By contrast, Atwater (1984), Atwater (1986)
identified at least 89 graded flood beds between 2000 to
3000 rhythmite beds. Arguing that each represented a
separate flood from glacial Lake Missoula over the period
13.35-15.55 ka BP, he found that backflooding occurred
every 35-55 years, with flood magnitude decreasing with
increasing frequency of flood occurrence. Varve frequency increased in the middle of the stratigraphic
sections, indicating that while flood frequency declined
(from every 25-40 years to every 50-55 years), flood
magnitude increased during the middle part of the glacial
phase, when the ice sheet was thicker. The final stages of
ice thinning and lake drainage were associated with
j6kulhlaup recurrence intervals reduced to only every 1-2
years (Baker and Bunker, 1985).
Many j6kulhlaup channelways are distinguished by
the presence of boulder fields and pavements, 'washed'
outwash and till surfaces, boulder lags, armoured
boulder-strewn terraces, and boulder erratics. Boulder
deposits have been recorded from many of the spillway
channels which carried j6kulhlaup meltwaters from
the Lake Agassiz basin (Matsch, 1983; Teller and
Thorleifson, 1987), Lake Nipigon (Teller and Thorleifson, 1983) and Lake Wisconsin (Clayton and Attig,
1987) where palaeoflood discharges ranged from
3x103 to 105 m 3 s -]. Boulder bars are also found in the
Missoula and Lake Bonneville flood routeways (Baker,
1973a; O'Connor, 1993), on the Icelandic sandurs
(Fig. 7; Maizels, 1992), on west Greenland j6kulhlaup
bars (Fig. 6), and form boulder lags within j6kulhlaup
sediment sequences (e.g. Fraser and Bleuer, 1988).
Extensive j6kulhlaup boulder deltas described from
northern Sweden exhibit discrete boulder lobes, streamlined scour marks, residual till remnants, and incised
channel networks (Elfstr6m, 1987). Boulder berms,
linear accumulations and clusters of large imbricated
boulders, are also found along the margins of many
cobble bars, forming the edge of the zone of flow
separation during j6kulhlaup floods (e.g. Russell,
1992, Russell, submitted).
Kettle Holes and Ice-block Obstacle Marks
A major feature of glacier burst floods is the transport
of large ice blocks through the proglacial meltwater
system and subsequent deposition on to bars within the
outwash zone. Two types of associated small-scale
landforms can develop, depending on flow conditions,
local bar topography and bar and ice block sedimentology. The most common feature is kettle holes, sometimes
forming pitted sandur areas where dead ice-marginal ice
has been buried and gradually melted out to form an
irregular topographic surface. However, most pitted
outwash may well result from the melting of huge
numbers of ice blocks transported by j6kulhlaup flows
(Russell et al., submitted). Large, buoyant blocks of ice
are transported downstream (especially by hyperconcentrated flows; see 6. below) into zones of decelerating and
expanding flow where they become stranded on areas of
maximum elevation, namely bar heads and channel
margins. Where debris-rich ice blocks have melted out,
bar deposits may be covered with kettle holes exhibiting
debris rims or may be filled with till to form mounds
(Figures 7-10; Maizels, 1992). Where flow continues
around the ice block, streamlined scour or obstacle marks
can develop (Fig. 11). Russell (1993) found, for example,
that during the waning stages of a recent j6kulhlaup in
west Greenland, ice blocks were deposited along the
edges of main channels and on the stoss sides of the main
bar units of a valley sandur. As in the case of normal rock
obstacles, Russell demonstrated that the size of ice blocks
entrained and transported by j6kulhlaups is related to the
transport capacity and depth of flow. The relationships
Quaternary Science Reviews: Volume 16
810
Type 1: 'Normal' kettle
hole
Type 2: 'Rimmed' kettle
OoO
Type 2: 'Crater' kettle
..
o . .
o
o,:,o
o
•
-
o
•
o
-,,o
.
-o
o
~'b
oC) o
Type 4: 'Till-fill' kettle
--_-
- o o o
0
0
0
~::~
°0¢~o
~
°
0
FIG. 10. Classification of j6kulhlaup kettle-hole forms shown
in cross-section, based on debris content of the original ice
bh)cks, ranging from clear ice blocks (Type I) to debrissaturated ice blocks (Type 4) (from Maizels, 1992).
found for the ice blocks closely reflected relationships
that have already been established between (i) the size
and shape of normal rock obstacles, and (ii) flow depth
and flow direction (e.g. Allen, 1984). Ice-block obstacle
marks are also characterised by distinctive sedimentology, as coarser grained material accumulates in the
shadow ridge downstream of the obstacle, while fines are
deposited in its immediate wake.
Glacio-volcanic J6kulhlaup Outwash
Glacio-volcanic j6kulhlaup outwash exhibits a distinctive suite of vertical lithofacies sequences, reflecting high
sediment concentrations during peak flows, and marked
changes in sediment characteristics associated with
changes in flow conditions and sediment fluxes during
the course of the j 6 k u l h l a u p . Although numerous
examples of volcanic fluvial deposits have been recorded
(Lajoie, 1984), the few glacio-volcanic examples available suggest that many similar features are present.
Many of the huge sandurs of south Iceland, for
example, are of glacio-volcanic j6kulhlaup origin. The
j6kulhlaups are characterised by extremely large volumes
of meltwater (up to 6 km~), much of which is stored in
subglacial craters prior to catastrophic drainage (Thorarinsson, 1957; Bj6rnsson, 1988). The glacio-volcanic
sandurs largely comprise a massive, black pumice granule
lithofacies at least 8 m thick, with very little variation in
median grain size (0.75-2.83 mm) and percentage fines
(below 3.5%) through the vertical sequence (Fig. 12A;
Jonsson, 1982: Maizels, 1989a, Maizels, 1989b, Maizels,
1991, Maizels, 1992, Maizels, 1993a, Maizels, 1995).
This type of massive granular outwash is defined here as a
Type F vertical profile (Table 3; redesignated from 'Type
A' in Maizels, 1991, Maizels, 1993a). Five sub-groups of
Type F profiles, from F5 to F I , can be distinguished,
exhibiting a progressive increase in internal structure, the
presence of boundary laminations, and improved sorting.
FIG. 11. Ice-block obstacle marks in a zone of flow expansion on a lateral bar of the Gigjukvisl River, Skeidararsandur,
south Iceland, as it exits the confines of Neoglacial moraine deposits. These features formed during j(~kulhlaup l]ows
probably generated from sudden drainage of Grimsv6tn. Flow was from right to left.
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
These profiles are interpreted as representing hyperconcentrated grain flow deposits containing varying
proportions of coarse clasts entrained from along the
flow path, with the continuum from F5 to F1 profiles
representing an increase in fluid flow and boundary shear
and traction transport of grains. They are regarded as
forming during peak flow or surge conditions when
sediment concentrations were at a peak. Deposits were
rapidly 'frozen' in situ following rapid dewatering of the
highly porous pumice medium.
The most widespread sequence forming the Icelandic
glacio-volcanic sandur plains is Type E4 (Fig. 12B).
These typically comprise up to 5 m of the massive
granule lithofacies underlain by crudely bedded gravels,
and overlain by up to 3.5 m of trough cross-bedded
granules, capped by thin, horizontally bedded sands and
granules. Type E4 profiles are interpreted as representing
a four-stage j6kulhlaup event comprising pre-surge
reworking of sandur gravels, an hyperconcentrated flood
surge, and post-surge waning stage flows associated with
rapidly migrating dunes, followed by shallow sheet flows
(Maizels, 1989a, b, 1991, 1992).
A range of graded granule lithofacies also occurs
within the Icelandic glacio-volcanic sandurs (Type D
lithofacies sequences; Table 3). Normally graded granules
(Type D1) are interpreted as a waning stage deposit
associated with declining competence; repeated, normally
graded cyclic sequences (Type D2) are interpreted as
representing deposition during the waning stages of
successive flood waves of a single j6kulhlaup; normalinverse (Type D3) and inversely graded lithofacies (Type
D4) are interpreted as hyperconcentrated grain flow
deposits in which dispersive stresses promoted the
upward migration of the coarser clasts towards the
surface. In both the latter types, the whole sediment unit
was moving as a single mass, and was deposited rapidly
on dewatering.
On steeper, ice-proximal slopes the glacio-volcanic
sandur deposits may contain clay-rich admixtures of
matrix-supported, heterogeneous clasts, interpreted as
debris flow deposits (Type G deposits; Table 3; and see
Eyles and Miall, 1984). These were probably generated
by high inputs of sediment from newly expanded, debrisrich glacial tunnelways occupied by the rising flood wave
(cf Jackson, 1979). However, because sandur slopes are
relatively low (generally below 0.03), and meltwater
volumes so high, debris flow deposits are rare beyond the
ice-proximal zone.
A number of sandur sites also contain highly deformed
sediments (Type H profiles; Table 3), locally exhibiting
steeply dipping crude bedding planes, folds, overfolds
and faults. Large masses of diamicton and compacted
gravels may be included along rising shear planes and
incorporated into higher lenses of the deposit. Imbrication
is distorted. Type H sediments are interpreted as
j6kulhlaup deposits that have been disturbed during
over-riding by, or convergence with, subsequent pulses
of flood flows, by entrainment of eroded bed, bank or icerafted materials, or by melting of incorporated ice masses.
Such situations arise where sediment-rich flows come
811
into contact with bed obstacles such as rock or till
protuberances, older substrate deposits, or ice blocks,
leading to deceleration and rapid dewatering, while
marked deformation of bedding can occur during rapid
deposition and settling of the flood deposit.
SPATIAL VARIABILITY IN L I T H O F A C I E S
DISTRIBUTIONS
Proximal-distal
Changes
Proximal-distal variations in sedimentology are normally highly distinctive in proglacial fluvial systems.
Type I and Type II sandurs (Table 1) are characterised by
strong downstream fining associated with a transition
from crudely horizontally bedded, proximal gravel beds
associated with longitudinal bars to more distinctly planeand cross-bedded sand and gravel beds produced by
migrating sand bars and fluvial dune and ripple systems in
distal areas (e.g. Boothroyd and Ashley, 1975; Boothroyd
and Nummedal, 1978; Miall, 1978; Rust, 1978). Bed
thickness also declines markedly downstream.
Marked contrasts in sedimentology were identified by
Russell (1992), Russell (submitted) over a 1 kin-long
valley sandur in west Greenland which is subject to
repeated j6kulhlaups (Fig. 2A, B). The proximal zone is
characterised by boulder berms, cobble sheets, poorly
sorted channel fills, composite lateral accretion deposits,
erosional channels, and ice-block grounding structures.
Vertical lithofacies sequences exhibit distinct Type H3
profiles, with Gp and Sp lithofacies overlain by massive
gravels, and capped by an imbricated cobble lag (Fig. 5).
This sequence is interpreted as representing bar front
migration during each successive j6kulhlaup, followed by
waning stage winnowing. The distal area is divided into
an upstream free-flow zone, and a downstream backwater
zone. In the former, lateral and downstream migration of
sand and gravel bars generated numerous Gp units
separated by reactivation surfaces, and overlain by sand
and gravel sheets and local fields of megaripples. As the
bars reach the deeper water of the backwater zone, planar
cross-stratification increases in scale. Within the backwater zone, bars become lobate with tabular foresets and
steep planar cross-stratification associated with bar fronts,
deltas or lobes forming at the mouths of chute channels
incised into the bar front. Coarse-grained lags result in
distinctive Type B2 profiles.
Glacio-volcanic outwash (Type III sandurs) may
exhibit ice-proximal lobes or fans deposited by debris
or hyperconcentrated flows, and dissected by later stage
fluid flows cutting deep flood channels. More distal zones
are characterised by more fluid flows, leaving areas of
'washed' sandur, streamlined residual bar forms bounded
by erosional channels and terrace sequences, and fields of
dunes, kettle holes and hummocky 'till-fill' kettles
(Fig. 7). Downstream fining and thinning occurs mostly
within the fluid flow lithofacies of the multistage outwash
deposits, while the hyperconcentrated flow lithofacies,
representing the main flood surge, shows minor fining
and thinning out downstream, but with some increased
812
Quaternao' Science Reviews: Volume 16
(A)
(B)
FIG. 12. (A) Massive, homogeneous pumice granules that form the bulk of the glacio-volcanic sandur deposits of south
Iceland. This is taken from a typical Type E vertical profile (see Table 3). (B) Vertical section ca 8 m high exhibiting a
typical Type E4 vertical lithofacies profile characteristic of the glacio-volcanic sandurs of south Iceland (from Maizels,
1991). Basal bedded pre-surge gravels are overlain by thick, massive Type F flood surge granules, capped by trough crossbedded and horizontally bedded post-surge granules.
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
development of internal laminations (cf Scott, 1988a,
Scott, 1988b; Maizels, t995).
Lateral Variations
Strong lateral variation in vertical lithofacies types
occurs within sandurs where j6kulhlaup flows have
encountered a range of different boundary conditions.
On the west Greenland valley sandur (Type II outwash),
for example, Russell (1992), Russell (submitted) identified
finer-grained lateral zones where bedding associated with
thin sheet gravels and trains of megaripples dip away from
the main channel (Figures 4 and 5). Some lateral sites were
characterised by upward fining sequences associated with
vertical bar growth (Type A1 profile). On Myrdalssandur
(Type IlI outwash), Maizels (1993a) identified distinctive
vertical lithofacies sequences associated with zones of
ponded water; expanding, constricted and converging
flows; flows across, and emerging from, a partially buried
lava field; and flows around bedrock obstacles.
MODELS OF PROGLACIAL J()KULHLAUP
OUTWASH DEPOSITS
It is clear from this review that the contrasts in
sedimentology between j6kulhlaup outwash and 'normal'
braided river outwash are so great that distinctive models
of j6kulhlaup outwash deposits need to be firmly
established.
Lithofacies Types
Building on earlier work by a number of authors,
including Maizels (1989a, b, 1991, 1993a, b), a model is
presented here that represents the relationship between
the different j6kulhlaup outwash deposits described in
this paper and (l) the nature of the flow (horizontal axis),
and (2) the sizes of sediment available (vertical axis)
(Fig. 13; modified from Maizels, 1989b)
In turbulent and macroturbulent fluid flows of Types I
and II outwash, the most common deposits are those of
expansion bars, and locally of eddy and pendant bars.
Expansion bars in Type II j6kulhlaup outwash are
normally composed of large-scale gravel-cobble crossbeds associated with downstream migration of the
accreting bar front, sometimes capped by an imbricated
boulder armour layer, to form a Type B2 vertical profile
(Table 3). J6kulhlaup flows transporting high sediment
loads can mantle outwash plains and proximal bar
deposits with large-scale gravel dunes, also composed
of large-scale cross-bedded units. According to the rate of
decrease in flood discharge, dune sequences may or may
not be capped by a coarse-grained armour layer (Type B2
and B 1 profiles, respectively).
Type II j6kulhlaup deposits characteristically contain
large percentages of cobble and boulders, and can form
extensive boulder fields, boulder pavements, crudely
horizontally bedded, imbricated boulder beds, or boulder
lobes (Type C profiles). In coarse sediments, j6kulhlaup
813
outwash comprises massive inverse-normally graded
cobble or boulder gravels (Type D5 profile), reflecting
deposition during both the rising and falling limbs of the
j6kulhlaup hydrograph.
Where flows become increasingly hyperconcentrated
(Type III outwash), deposits may form ice-proximal lobes
and fans, with more fluid sheets spreading across
downstream sandur plains. Sediment sequences become
dominated by Type E4 profiles, in which the record of the
full hydrograph may be preserved. Thin, pre-surge basal
gravels incorporating rip-up clasts of soil and older
outwash, are overlain by thick, massive, hyperconcentrated surge gravels or granules. These are truncated by
post-surge trough cross-bedded units representing rapidly
aggrading and migrating dunes, capped by waning stage,
horizontally laminated sands and silts. Downstream and
lateral variations in flow conditions lead to limited
deviations from this characteristic sequence. Most
commonly these take the form of normal-inversely graded
(Type D3 profiles) and inversely graded (Type D4
profiles) gravels or granules associated with more
cohesive flows.
At high sediment concentration runoff may also take
the form of ice-proximal debris flows, leading to localised
deposition of lobes and tongues of massive, matrixsupported, heterogeneous gravels, including erratics,
former ice blocks, flow structures and rip-up clasts (Type
G profile). Similarly, outwash deposits containing
deformed bedding, erratics, rip-up clasts, and masses of
diamicton (Type H profile) result from over-riding of
successive flood waves or entrainment of erodible
substrate materials. Finally, fine-grained sands and silts
can accumulate locally from suspension, or as turbidity
currents, in zones of slack water, in backwater reaches
and areas of temporarily ponded water. These sediments
include both finer-grained rhythmite horizons and interbedded coarser-grained 'flood beds' (profile Types A3
and A4, which can be found in all outwash types).
Landscape Characteristics
Landscape models for Types II (Fig. 14) and III
j6kulhlaup outwash (Fig. 15) indicate some of the
relationships so far established between landforms, bedforms and sedimentary sequences for j6kulhlaup deposits in proglacial areas. The landscape model for Type
II outwash (limno-glacial j6kulhlaup outwash; Fig. 14)
highlights the formation of large-scale expansion bars
downstream of a constricted channel zone, such as a
lake drainage spillway. The bar deposits are composed
of upward coarsening, crudely bedded gravels, cobbles
and boulders, mantled with an imbricated boulder
lag, waning stage sand and silt horizons, or distal ripple
trains, and bounded by large-scale cross-bedding at
the bar front. Kettle holes and pitted outwash characterise parts of the bars, together with ice block obstacle
marks and chute channels. Trains of giant dunes
represent zones of deeper, faster water transporting high
loads of sand and gravel, and associated with large-
814
Quaternary Science Reviews." Volume 16
CHARACTERISTICS
OF
FLUID SEDIMENT
MIX
LAMINAR<
~TURBULENT
1 0 0 % ¢ HIGH ¢ ( 7 0 % ) SEDIMENT CONCENTRATION (40%)
LOW. :~(0%)
NON - N E W T O N I ~ I N G H A M
,,,NEWTONIAN
DFLUIDAL
COHESIVE(~.,
D COHESIONLESS
VISCOUS, HIGH YIELD S T R E N G T H ~ : ~
NON -VISCOUS, LOW YIELD STRENGTH
FLOW TYPE
DEBRIS FLOWS ~____r_HYPERCONCENTRATED GRAIN F L O W S . ~ F L U I D
DOMINANT
CLAST- SUPPORT
MECHANISM
BUOYANCY
YIELD STRENGTH
-
DISPERSIVE STRESS
l/~ TURBULENCE
HYPERCONCENTRATED SURGE DEPOSITS
.- ' -
.
.
.
I/
F-
c
,
\
c
. .--~
:":'~':::~ .'-':::"::
~ ,
\
f
~
I
r~
>
o ~
t
f
MATRIX -
~
s-P .....
,
-
i:,
eel
~'~'.:0'
"'
£3
S
~
E4
~ I
~
~
I
':'
I
I
"
POORLY
SORTED
RA
r~_oo#~-~
u-~
1 ~ 6
~ .
NON~RADED
.
~~
'
:..O.
'L"
f
-~^ '.1~:1
•
,'.-~.:"'~'
:"/--i"+
:l
~%xil~i],:~
~
INVERSELY
GRADED
POORLY
SORTED
D4
.
A1
~L°..,~',
~i~'C';'~
~'~."o..ooo., 1. •
"" "'°° °" °'
['-~"~.{
,~.'~.~
I
°1[
,~.:.~1
~;~c.~.,.~..
~
~"(~"" ~
D3
A1
'0• •~°o;#s~..
v ..... "'+i
i":"+ °'°°~
G~NO~D LY
POORLY
S~D
FLUVIAL
GRAVELS
~ . b ; O * 41i~
•~ % : . - o . ~ (
>,,
RISING
FLOW
SEQUENCE
,o,
c
f
SEDIMENT SIZE
~--:k::'..%
" "":
,~) ~,,-~
'.J.- .~° .~ (~': .'. "L "
o , .' • : . , ~ '
'
'
:.":
• " ~". " ,", :- . • "
,
"" "" "":l "'1 . • .: • ;
".;-i-:-. I......_.:_
c
IlL
SURGE DEPOSITS
~ k
"'~ i~ :~[
PRE- SURGE DEPOSIT~'e~r'~(~" "(~ [--::'~':.:~k'~
v~:
~r~q
,[~ll~ql~ ~:.:o.~;~
~SmVE,
....I ] . . . " C . " o .I
LJ- F" 0'.': °'" "J
k
E3
~
I LAMINATED
]lm
i
A
::."::!:."
,';'"..'.<~}'~'" "~
I °.," "f'~
' L¢ / ~
-
~
,". o',...'...~'. - ~, ~, POORLY STRUCTURED
"o"..;i : [~O " ";I NON-GRADED I
'. ' .~7~)'-',' ~| WELLSORTED
I
..
/
-
I
A1
POSTSURGE
INTERSURGE
DEPOS TS
~ 1
-T:i. il &ss,vE
.-
c
....
~'~
G
4/
l~'~
/'/ ~
./7
.
I FLUWALBEDFORMS
"".'.'":"" ":'.";".-'., .'.:':~
1 \
,
. ~q
FLOWS
KEY
~
I :.".'-."~:::+;~,..
f
)
A1
SILTS
I
SANDS
GRAVELS
COBBLES+
BOULDERS
c
SEDIMENT SIZE
FIG. 13. Vertical lithofacies profiles of outwash deposits, classified according to the characteristics of the fluid-sediment
mix and relative availability of sediment (horizontal axis) and size distribution of the source sediments (vertical axis).
c = coarse-grained materials: f : fine-grained materials• See Table 3 for key to profile notation (modified from Maizels,
1993a).
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
FIG. 14. Model of valley sandur development in an area of limno-glacial jrkulhlaup drainage downstream of a spillway
channel, generating expansion, eddy and pendant bars, trains of megaripples, boulder lags, and large-scale cross-bedding.
Key to notation: (1) expansion bar; (2) pendant bar; (3) megaripples or dunes; (4) slack-water deposits; (5) large-scale dune
cross-bedding with reactivation surfaces; (6) large-scale bar front cross-bedding; (7) imbricated boulder lag; (8) channel fill
deposits; (9) small-scale ripples; (10) chute channels and lobes; (11) kettle holes and kettle fills; (12) ice-block obstacle
marks; and (13) wash limit on adjacent valley-side slopes.
FIG. 15. Model of outwash development in an area of volcano-glacial j6kulhlaup drainage, generating lobate fans,
streamlined residual hummocks, and hyperconcentrated flood sequences (modified from Maizels, 1991). Key to notation: (1)
stacked sequences of multistage massive granular sediments, especially Type E4 sequences (see Table 3 and text); (2)
terraced boulder deposits; (3) high level, abandoned sandur surface exhibiting thin gravel horizon and braided palaeochannel
networks; (4) 'washed' sandur; (5) lobate fan deposited by hyperconcentrated jrkulblaup flows; (6) incised j6kulhlaup
channel with streamlined residual hummocks, boulders and megaripples; (7) hummocky distal j6kulhlaup deposit; (8)
streamlined, hummocky, erosional bars mantled with rimmed and till-fill kettles; (9) incised jrkulhlaup channel; (10) incised
active meltwater channel; (11) streamlined erosional bars, wash limits and scattered boulders and dune forms downstream of
bedrock obstacles.
815
816
Quaternary Science Reviews: Volume 16
scale cross-bedded units. Eddy bar deposits become
finer grained upstream in tributary valleys where they
become intercalated with slack-water sediments, while
pendant bars downstream of bedrock obstacles exhibit
streamlined tail deposits.
The landscape model for Type III outwash (volcano-glacial j6kulhlaup outwash; Fig. 15) indicates that
the more proximal sandur zones are commonly associated with debris lobes or h y p e r c o n c e n t r a t e d fan
deposits incised by flood channels leaving streamlined
residual hummocks, boulder fields, and trains of large
ripples or giant dunes. Aggradational bar forms are
indistinct or absent, and instead comprise extensive
areas of ' w a s h e d ' gravel sandur or finer sediments
dissected by fluid waning flows into erosional bar
forms. These are mantled with fields of kettle holes,
including ' r i m m e d ' or 'till-fill' kettles to form a pitted
or hummocky surface, and bounded by incised channels
and terraces. The deposits comprise stacked sequences
of multistage granular sediments deposited during single
flood hydrographs, and separated by boulder or gravel
lags.
SUMMARY AND CONCLUSION
This review demonstrates that j6kulhlaups do produce
distinctive a s s e m b l a g e s o f landforms and sediment
sequences, associated with high stream powers and coarse
sediment supply. In summary, six main lithofacies
sequences or assemblages can be identified as characterising j6kulhlaup deposits in proglacial areas:
(1) L a r g e - s c a l e c r o s s - b e d d i n g with a r m o u r capping
(Type B2), especially in Type II outwash;
(2) Boulder beds (Type C), in Types II and III outwash
(3) Inversely graded gravels, granules or boulder beds
(Types D3 to D5), in Types II and III outwash;
(4) Massive, structureless, matrix-poor gravels, granules
or boulder beds, underlain by basal bedded gravels,
and capped by fluid bedforms (Type E4), especially
in Type III outwash;
(5) Laminated sands and silts in backwater locations
(Types A3/A4), in Types II and III outwash; and
(6) Localised massive, matrix-supported diamicton units
and deformed bedding containing rip-up clasts (Types
G and H), in Types II and III, and Type III, outwash,
respectively.
The dominant and minor lithofacies types associated
with each sequence are given in Table 3.
Further work is required to refine these models and, in
particular, to develop predictive relationships between
hydraulic conditions and the resulting landforms and
sediments. The field base needs to be extended, and
appropriate numerical modelling techniques need to be
developed. The models are intended to provide a working
framework for the identification and interpretation of
proglacial j6kulhlaup deposits from the morphologic and
sedimentologic record.
REFERENCES
Allen, J.R.L. (1982) Late Pleistocene (Devensian) glaciofluvial
outwash at Bane-y-Warren, near Cardigan (West Wales).
Geological Journal 17, 3147.
Allen, J.R.L. (1984) Sedimentao, Structures: Their Character
and Physical Basis, Vol. 2. Elsevier.
Atwater, B.F. (1984) Periodic floods from Glacial Lake
Missoula into the Sanpoil Arm of Glacial Lake Columbia,
northeastern Washington. Geology 12, 464467.
Atwater, B.F. (1986) Pleistocene glacial-lake deposits of the
Sanpoil River Valley, northeastern Washington. U.S. Geological Survey Bulletin 1661, 39 pp.
Baker, V.R. (1973a) Paleohydrology and sedimentology of Lake
Missoula flooding in Eastern Washington. Geologieal SocieO,
of America Special Palter 144, 73 pp.
Baker, V.R. (1973b) Erosional forms and processes for the
catastrophic Missoula floods in eastern Washington. In
Fluvial Geomorphology, ed. M. Morisawa, pp. 123-148.
Allen and Unwin.
Baker, V.R. (1978) Paleohydraulics and hydrodynamics of
scabland floods. In The Channelled Scabland: Comparative
Planeta O' Geology. Field Col!ference Guidebook, eds V.R.
Baker and D. Nummedal, pp. 59 79. Columbia Basin,
Washington, DC.
Baker, V.R. (1983) Paleoflood hydrologic analysis from slackwater deposits. Quaternary Studies in Poland 4, 19-26.
Baker, V.R. (1984) Flood sedimentation in bedrock fluvial
systems. In Sedimentology of Gravels and Conglomerates,
eds E.H. Koster and R.J. Steel, pp. 87-98. Canadian Society
of Petroleum Geologists, Memoir 10.
Baker, V.R., Benito, G. and Rudoy, A.N. (1993) Paleohydrology of Late Pleistocene superflooding, Altay Mountains, Siberia. Science 259, 348-350.
Baker, V.R. and Bunker, R.C. (1985) Cataclysmic late
Pleistocene flooding from Glacial Lake Missoula: a review.
Quaternary Science Reviews 4, IM-1.
Baker, V.R. and Costa, J.E. (1987) Flood power. In Catastrophic
Flooding, eds L. Mayer and D. Nash, pp. 1-25. Allen and
Unwin.
Baker, V.R., Kochel, R.C., Patton, P.C. and Pickup, G. (1983)
Palaeohydrologic analysis of Holocene slack-water sediments. In Modern and Ancient Fluvial Systems, eds J.D.
Collinson and J. Lewin, pp. 229-239. Blackwell.
Beecroft, 1. (1983) Sediment transport during an outburst from
Glacier de Tsidjiore, Switzerland, 16-19 June 198 I. Journal
of Glaciology 29, 185-190.
Bj6rnsson, H. (1988) Hydrology of ice caps in volcanic regions.
Visindqfelag lslendiga, Societas Seientarum lslandica, XLV,
Reykjavik, 139 pp.
Boothroyd, J.C. and Ashley, G.M. (1975) Processes, bar
morphology, and sedimentary structures on braided outwash
fans, northeastern Gulf of Alaska. In Glaci(~fTuvial and
Glaciolacustrine Sedimentation, eds A.V. Jopling and B.C.
McDonald, pp. 193-222. Society of Economic Paleontologists and Mineralogists Special Publication No. 23.
Boothroyd, J.C. and Nummedal, D. (1978) Proglacial braided
outwash: a model for humid alluvial-fan deposits. In Fluvial
Sedinwntology, ed. A.D. Miall, pp. 641-668. Canadian
Society of Petroleum Geologists Memoir 5.
Bretz, J.H. (1926) The Spokane flood beyond the channeled
scablands. Journal of Geology 33, 96 115.
Brodzikowski, K. and van Loon, A.J. (1991) Glacigenic
Sediments. Developments in Sedimentology 49, 674 pp.
Carling, P. (1996a) Morphology, sedimentology and palaeohydraulic significance of large gravel dunes, Altai Mountains,
Siberia. Sedimentology 43 (in press).
Carling, P. (1996b) A preliminary palaeohydraulic model
applied to Late-Quaternary gravel dunes: Altai Mountains,
Siberia. In Global Continental Changes: the Context (~f"
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
Palaeohydrology, eds J. Branson, A.G. Brown and K.J.
Gregory. Geological Society of London (in press).
Carter, R.M. (1975) A discussion and classification of subaqueous mass-transport with particular attention to grain-flow,
slurry-flow and fluxoturbidites. Earth Science Reviews 11,
145-177.
Church, M. (1972) Baffin Island sandurs: a study of arctic
fluvial processes. Geological Society of Canada Bulletin 216,
208 pp.
Church, M. (1978) Palaeohydrological reconstructions from a
Holocene valley fill. In Fluvial Sedimentology, ed. A.D.
Miall, pp. 743-772. Canadian Society of Petroleum Geologists, Memoir 5.
Church, M. (1988) Floods in cold climates. In Flood
Geomorphology, eds V.R. Baker, R.C. Kochel and P.C.
Patton, pp. 205-229. John Wiley & Sons.
Church, M. and Gilbert, R. (1975) Proglacial fluvial and
lacustrine environments. In Glaciofluvial and Glaciolacustrine Sedimentation, eds A.V. Jopling and B.C. McDonald,
pp. 22-100. Society of Economic Paleontologists and
Mineralogists Special Publication No. 23.
Clague, J.J. and Mathews, W.H. (1973) The magnitude of
j6kulhlaups. Journal of Glaciology 12, 501-503.
Clague, J.J. and Rampton, V.N. (1982) Neoglacial Lake Alsek.
Canadian Journal of Earth Sciences 19, 94-117.
Clague, J.J. (1975) Sedimentology and paleohydrology of Late
Wisconsinan outwash, Rocky Mountain Trench, Southeastern
British Columbia. In Glaciofluvial and Glaciolacustrine
Sedimentation, eds A.V. Jopling and B.C. McDonald, pp.
223-237. Society of Economic Paleontologists and Mineralogists Special Publication No. 23.
Clarke, G.K.C. (1982) Glacier outburst floods from 'Hazard
Lake', Yukon Territory, and the problem of flood magnitude.
Journal of Glaciology 28, 3-21.
Clarke, G.K.C. and Mathews, W.H. (1981) Estimates of the
magnitude of glacier outburst floods from Lake Donjek,
Yukon Territory, Canada. Canadian Journal of Earth
Sciences 18, 1452-1463.
Clarke, G.K.C., Mathews, W.H. and Pack, R.T. (1984) Outburst
floods from Lake Missoula. Quaternary Research 22, 289299.
Clayton, L. and Attig, J. (1987) Drainage of Lake Wisconsin
near the end of the Wisconsin glaciation. In Catastrophic
Flooding, eds L. Mayer and D. Nash, pp. 139-155. Allen and
Unwin.
Costa, J.E. (1983) Paleohydraulic reconstruction of flash-flood
peaks from boulder deposits in the Colorado Front Range.
Geological Society of America Bulletin 94, 986-1004.
Costa, J.E. (1984) Physical geomorphology of debris flows. In
Developments and Applications of Geomorphology, eds J.E.
Costa and P.J. Heister, pp. 268-317. Springer-Verlag, Berlin.
Costa, J.E. (1988a) Rheologic, geomorphic and sedimentologic
differentiation of water floods, hyperconcentrated flows, and
debris flows. In Flood Geomorphology, eds V.R. Baker, K.C.
Kochel and P.C. Patton, pp. 113-122. John Wiley & Sons.
Costa, J.E. (1988b) Floods from dam failures. In Flood
Geomorphology, eds V.R. Baker, K.C. Kochel and P.C.
Patton, pp. 439-463. John Wiley & Sons.
Costello, W.R. and Walker, R.G. (1972) Pleistocene sedimentology, Credit River, Southern Ontario: a new component of
the braided river model. Journal of Sedimentary Petrology
42, 389-400.
Craig, R.G. (1987) Dynamics of a Missoula flood. In
Catastrophic Flooding, eds L. Mayer and D. Nash, pp.
305-333. Allen and Unwin.
Dawson, M. and Gardiner, V. (1987) River terraces: The general
model and a palaeohydrologic and sedimentological interpretation of the terraces of the Lower Severn. In Palaeohydrology in Practice. A River Basin Analysis, eds K.J.
Gregory, J. Lewin and J.B. Thornes, pp. 269-305. John
Wiley & Sons.
817
Ehlers, J. and Grube, F. (1983) Meltwater deposits in north-west
Germany. In Glacial Deposits in North-west Europe, ed. J.
Ehlers, pp. 249-256.A.A. Balkema.
Elfstrrm, A. (1983) The Baldakatj boulder delta, Lapland,
Northern Sweden. Geografiska Annaler 65A, 201-225.
Elfstrrm, A. (1988) Late glacial hydrology of the Upper Pite
River Valley, Swedish Lapland. Geografiska Annaler 70A,
99-123.
Elfstrrm, A. (1987) Large boulder deposits and catastrophic
floods. Geografiska Annaler 69A, 101-121.
Eyles, N. and Miall, A.D. (1984) Glacial Facies. In Facies
Models, ed. R.G. Walker, pp. 15-38. Geoscience Canada
Reprint Series 1.
Fahnestock, R.K. and Bradley, W.C. (1973) Knik and
Matanuska rivers, Alaska: a contrast in braiding. In Fluvial
Geomorphology, ed. M. Morisawa, pp. 220-250. Allen and
Unwin.
Fenn, C. (1987) Sediment transfer processes in alpine glacier
basins. In Glacio-Fluvial Sediment Transfer. An Alpine
Perspective, eds A.M. Gurnell and M.J. Clark, pp. 59-85.
John Wiley & Sons.
Fisher, R.V. (1971) Features of coarse-grained, high-concentration fluids and their deposits. Journal of Sedimentary
Petrology 41, 916-927.
Fraser, G.S. and Bleuer, N.K. (1988) Sedimentological consequences of two floods of extreme magnitude in the late
Wisconsinan Wabash Valley. Geological Society of America
Special Paper 229, 111-125.
Gurnell, A.M. (1987) Suspended sediment. In Glacio-Fluvial
Sediment Transfer: An Alpine Perspective, eds A.M. Gurnell
and M.J. Clark, pp. 305-354. John Wiley & Sons.
Hammer, K.M. and Smith, N.D. (1983) Sediment production
and transport in a proglacial stream: Hilda Glacier, Alberta,
Canada. Boreas 12, 91-106.
Harrison, S. and Fritz, W.J. (1982) Depositional features of
March 1982 Mount St. Helens sediment flows. Nature 299,
720-722.
Jackson, L.E.Jr. (1979) A catastrophic glacial outburst flood
(jrkulhlaup) mechanism for debris flow generation at the
Spiral Tunnels, Kicking Horse River basin, British Columbia.
Canadian Geotechnical Journal 16, 806-813.
Jarrett, R.D. and Malde, H.E. (1987) Paleodischarge of the late
Pleistocene Bonneville Flood, Snake River, Idaho, computed
from new evidence. Geological Survey of America Bulletin
99, 127-134.
Johnson, A.M. (1970) Physical Processes in Geology. Freeman
Cooper, San Francisco.
Jonsson, J. (1982) Notes on the Katla volcanological debris
flows. Jokull 32, 61-68.
Kehew, A.E. (1982) Catastrophic flood hypothesis for the origin
of the Souris Spillway, Saskatchewan and North Dakota.
Geological Society of North America Bulletin 93, 1051-1058.
Kehew, A.E. and Clayton, L. (1983) Late Wisconsin floods and
development of the Souris-Pembina spillway system in
Saskatchewan, North Dakota and Manitoba. In Glacial Lake
Agassiz, eds J.T. Teller and L. Clayton, pp. 187-209.
Geological Association of Canada, Special Paper 26.
Kehew, A.E. and Lord, M.L. (1986) Origin and large-scale
erosional features of glacial-lake spillways in the northern
Great Plains. Geological Society of America Bulletin 97, 162177.
Kehew, A.E. and Lord, M.L. (1987) Glacial outbursts along the
mid-continental margins of the Laurentide ice sheet. In
Catastrophic Flooding, eds L. Mayer and D. Nash, pp. 95121. Allen and Unwin.
Kochel, R.C. and Baker, V.R. (1988) Paleoflood analysis using
slackwater deposits. In Flood Geomorphology, eds V.R.
Baker, R.C. Kochel and P.C. Patton, pp. 357-376. John Wiley
& Sons.
Lajoie, J. (1984) Volcaniclastic rocks. In Facies Models, ed.
R.G. Walker, pp. 39-52. Geoscience Canada Reprint Series 1.
818
Quaternary Science Reviews: Volume 16
Lawson, D. (1982) Mobilization, movement and deposition of
active subaerial sediment flows, Matanuska Glacier, Alaska.
Journal of Geology 90, 279-300.
Maizels, J.K. (1983) Palaeovelocity and palaeodischarge
determination for coarse gravel deposits. In Background to
Palaeohydrology, ed. K.J. Gregory, pp. 101-139. John Wiley
& Sons.
Maizels, J.K. (1987) Modelling of paleohydrologic changes
during deglaciation. Geographie Physique et Quaternaire 40,
263-277.
Maizels, J.K. (1989) Sedimentology, paleoflow dynamics and
flood history of j6kulhlaup deposits: paleohydrology of
Holocene sediment sequences in southern Iceland sandur
deposits. Journal of Sedimenta©" Petrology 59, 204-223.
Maizels, J.K. (1989b) Sedimentology and palaeohydrology of
Holocene flood deposits in front of a j(Skulhlaup glacier,
South Iceland. In Floods. Hydrological, Sedimentological
and Geomorphological Implications: an Overview, eds K.
Bevan and P. Carling, pp. 239-253. John Wiley & Sons.
Maizels, J.K. (1991) Origin and evolution of Holocene sandurs
in areas of j6kulhlaup drainage, south Iceland. In Environmental Change in Iceland: Past and Present, eds J.K. Maizels
and C. Caseldine, pp. 267-302. Kluwer Academic Publishers.
Maizels, J.K. (1992) Boulder ring structures produced during
j6kulhlaup flows. Origin and hydraulic significance. Geografiska Annaler 74A, 21-33.
Maizels, J.K. (1993) Lithofacies variations within sandur
deposits: the role of runoff regime, flow dynamics and
sediment supply characteristics. Sedimentary Geology 85,
299-325.
Maizels, J.K. (1993b) Quantitative regime modelling of fluvial
depositional sequences: application to Holocene stratigraphy
of humid-glacial braid-plains (Icelandic sandurs). In Characterisation of Fluvial and Aeolian Reservoirs, eds C.P.
North and D.J. Prosser, pp. 53-78. Geological Society Special
Publication No 73.
Maizels, J.K. (1994) The geomorphic significance of jOkulhlaup
drainage on Icelandic sandar: morphological and stratigraphic
basis for modelling long-term (Holocene) sandur evolution.
In Environmental Change in Iceland, eds J. Stotter and F.
Wilhelm, pp. 122-204. Munchener Geographische Abhandlungen, Reihe B, Band B 12.
Maizels, J.K. (1995) Sediments and landforms of modern
proglacial terrestrial environments. In Modern Glacial
Environments. Processes, Dynamics and Sediments, ed. J.
Menzies, pp. 365-416. Butterworth-Heinemann.
Maizels, J.K. (1997) Palaeohydrology from fluvioglacial sediments: potential for inferring glacier variations. In Palaoklimaforschung/Palaeoclimate Research, ed. B. Frenzel (in
press).
Maizels, J.K. and Russell, A.J. (1992) Quaternary perspectives
on j6kulhlaup prediction. Quaternary, Proceedings 2, 133
152.
Malde, H.E. (1968) The catastrophic Late Pleistocene Bonneville Flood in the Snake River Plain, Idaho. US Geological
Survey Professional Paper 596, 52 pp.
Matsch, C.L. (1983) River Warren, the southern outlet of
Glacial Lake Agassiz. In Glacial Lake Agassiz, eds J.T. Teller
and L. Clayton, pp. 231 244. Geological Association of
Canada Special Paper 26.
Matthes, G.H. (1947) Macroturbulence in natural stream flow.
American Geophysical Union Transactions 28, 255-262.
Miall, A.D. (1977) A review of the braided-river depositional
environment. Earth Science Reviews 13, 1-62.
Miall, A.D. (1978) Lithofacies types and vertical profile models
in braided river deposits: a summary. In Fluvial Sedimentology, ed. A.D. Miall, pp. 597-604. Canadian Society of
Petroleum Geologists Memoir 5.
Miall, A.D. (1980) Cyclicity and the facies model concept in
fluvial deposits. Canadian Petroleum Geology Bulletin 28,
59-80.
Miall, A.D. (1983) Glaciofluvial transport and deposition. In
Glacial Geology, ed. N. Eyles, pp. 168-183. Pergamon Press.
Nemec, W. and Steel, R.J. (1984) Alluvial and coastal
conglomerates: their significant features and some comments
on gravelly mass-flow deposits. In Sedimentology of Gravels
and Conglomerates, eds E.H. Koster and R.J. Steel, pp. 1-31.
Canadian Society of Petroleum Geologists Memoir 10.
O'Connor, J.E. (1993) Hydrology, hydraulics, and geomorphology of the Bonneville Flood. Geological Society qfAmerica
Special Paper 274, 83 pp.
O'Connor, J.E. and Webb, R.H. (1988) Hydraulic modelling for
paleoflood analysis. In Flood Geomorphology, eds V.R.
Baker, R.C. Kochel and P.C. Patton, pp. 393-402. John Wiley
& Sons.
Pardee, J.T. (1942) Unusual currents in glacial Lake Missoula,
Montana. Geological Society of America Bulletin 53, 15691600.
Patton, P.C., Baker, V.R. and Kochel, R.C. (1979) Slack-water
deposits: a geomorphic technique for the interpretation of
fluvial paleohydrology. In Adjustments of the Fluvial System,
eds D.D. Rhodes and G.P. Williams, pp. 225 253. Allen and
Unwin.
Pierson, T.C. (1981) Dominant particle support mechanisms in
debris flows at Mr. Thomas, New Zealand, and implications
for flow mobility. Sedimentology 28, 49-60.
Pierson, T.C. and Scott, K.M. (1985) Downstream dilution of a
lahar: transition from debris flow to hyperconcentrated
streamflow. Water Resources Research 21, 1511-1524.
Postma, G. (1986) Classification ~k)r sediment gravity-flow
deposits based on flow conditions during sedimentation.
Geology 14, 291 294.
Reed, E.C., Dreeszen, V.H., Bayne, C.K. and Schultz, C.B.
(1965) The Pleistocene in Nebraska and northern Kansas. In
The Quaternary of the United States, eds H.E. Wright Jr and
D.G. Frey, pp. 187-202, Princeton University Press.
Rist, S. (1983) Floods and flood danger in Iceland. Jokull 33,
119-132.
R6thlisberger, H. and Lang, H. (1987) Glacial hydrology. In
Glacio-fluvial Sediment Tran,sfer: An Alpine Perspective, eds
A.M. Gurnell and M.J. Clark, pp. 207 274. John Wiley &
Sons.
Rudoy, A.N. and Baker, V.R. (1993) Sedimentary effects of
cataclysmic Late Pleistocene glacial outburst flooding, Altay
Mountains, Siberia. Sedimentary Geology 85, 53 62.
Russell, A.J. (1989) A comparison of two recent j6kulhlaups
from an ice-dammed lake, Sondre Stromfjord, West Greenland. Journal of Glaciology 35, 157-162.
Russell, A.J. (1992) Geomorphological effects of j6kulhlaups,
west Greenland. Ph.D. Thesis, University of Aberdeen.
Russell, A.J. (1993) Obstacle marks produced by flow around
stranded ice blocks during a glacier outburst flood (j6kulhlaup) in west Greenland. Sedimentology 40, 1091-1111.
Russell, A.J. (submitted) The morphology and sedimentology of
a valley-confined sandur subject to j6kulhlaups, Kangerlussuaq, west Greenland. Earth SurJ}~ce Processes and Land-
fornls.
Russell, A.J., Knudsen, O., Maizels, J.K. and Marren, P. (in
prep.) Geomorphic impact and modelling implications of the
November 1996 j6kulhlaup, Skeidararsandur, Iceland.
Rust, B. (1978) Depositional models R)r braided alluvium. In
Fluvial Sedimentology, ed. A.D. Miall, pp. 605-625.
Canadian Society of Petroleum Geologists Memoir 5.
Scott, K.M. (1988a) Origin, behavior, and sedimentology of
prehistoric catastrophic lahars at Mount St. Helens, Washington. In Sedimentologic Consequences of Convulsive
Geologic Events, ed. H.E. Clifton, pp. 29-36. Geological
Society of America Special Paper 229.
Scott, K.M. (1988b) Origins, behavior, and sedimentology of
lahars and lahar-runout flows in the Toutle-Cowlitz river
system, Mount St. Helens, Washington. US Geological
Survey Prqlbssional Paper 1447-A, 74pp.
J. Maizels: J6kulhlaup Deposits in Proglacial Areas
Smith, G.A. (1986) Coarse-grained nonmarine volcaniclastic
sediment: terminology and depositional process. Geological
Society of America Bulletin 97, 1-10.
Smith, N.D. (1985) Proglacial fluvial environments. In Glacial
Sedimentary Environments, eds G.M. Ashley, J. Shaw and
N.D. Smith, pp. 85-134. Society for Economic Paleontologists and Mineralogists, Short Course Lecture Notes No 16.
Spring, U. and Hutter, K. (1981) Numerical studies of
j6kulhlaups. Cold Regions Science and Technology 4, 227244.
Sturm, M., Beget, J. and Benson, C. (1987) Observations of
j6kulhlaups from ice-dammed Strandline Lake, Alaska:
implications for paleohydrology. In Catastrophic Flooding,
eds L. Mayer and D. Nash, pp. 79-94. Allen and Unwin.
Teller, J.T. (1990) Volume and routing of Late-Glacial runoff
from the southern Laurentide ice sheet. Quaternary Research
34, 12-23.
Teller, J.T. and Thorleifson, L.H. (1983) The Lake AgassizLake Superior connection. In Glacial Lake Agassiz, eds J.T.
Teller and L. Clayton, pp. 261-290. Geological Association
of Canada Special Paper 26.
Teller, J.T. and Thorleifson, L.H. (1987) Catastrophic flooding
into the Great Lakes from Lake Agassiz. In Catastrophic
Flooding, eds L. Mayer and D. Nash, pp. 121-139. Allen and
Unwin.
Thorarinsson, S. (1957) The j6kulhlaup from the Katla area in
1955 compared with other j6kulhlaups in Iceland. Jokull 7,
21-25.
819
Thorson, R.M. (1989) Late Quaternary palaeofloods along the
Porcupine River, Alaska: implications for regional correlation. US Geological Survey Circular 1026, 51-54.
Thorson, R.M. and Dixon, E.J. (1983) Alluvial history of the
Porcupine River, Alaska: Role of glacial-lake overflow from
northwest Canada. Geological Society of America Bulletin 94,
576-589.
Tomasson, H. (1974) Grimsvatnahlaup 1972, mechanism and
sediment discharge. Jokull 24, 27-39.
Tomasson, H., Palsson, S. and Ingolfsson, P. (1980) Comparison
of sediment load transport in the Skeidara j6kulhlaups in
1972 and 1976. Jokull 30, 21-33.
Vincent, J.-S. (1984) Quaternary stratigraphy of C a n a d a - A
Canadian contribution to IGCP Project 24. Geological Survey
of Canada Paper 84-10, 87-100.
Waitt, R.B. (1980) About forty last-glacial Lake Missoula
j6kulhlaups through southern Washington. Journal of Geology 80, 653-679.
Waitt, R.B. (1984) Periodic j6kulhlaups from Pleistocene
Glacial Lake Missoula - - new evidence from varved
sediment in northern Idaho and Washington. Quaternary
Research 22, 46-58.
Waitt, R.B. (1985) Case for periodic, colossal j6kulhlaups from
Pleistocene glacial Lake Missoula. Geological Society of
America Bulletin 96, 1271-1286.