•
I
-*
Stripping of Keanakakoi tephra on Kilauea Volcano, Hawaii
MICHAEL C. MALIN Department of Geology, Arizona State University, Tempe, Arizona 85287
DANIEL DZURISIN U.S. Geological Survey, Cascade Volcano Observatory, Vancouver, Washington 98661
ROBERT P. SHARP Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125
ABSTRACT
Morphological characteristics, erosional
processes, and effects of burial and exhumation by debris mantles on basaltic volcanic
landforms have been evaluated through
field study of the Keanakakoi Formation, a
basaltic tephra formed in 1790 by phreatomagmatic eruptions from Kilauea caldera,
Hawaii. The upper coarse lithic, intermediate fine vitric, and lower mixed members
of this formation play different roles in the
creation of micro-terrain elements during
stripping of tephra from the underlying
bedrock. Of the seven micro-terrain elements defined, bedrock, scabby upland
surfaces, and lag gravels are the most distinctive and widely distributed. Different
proportions and combinations of microterrain elements define five zones of progressive deterioration of the Keanakakoi
tephra blanket southwestward from Kilauea
caldera into the Kau Desert. Fluvial and
eolian processes operate on different time
scales and at different locations, governed
by blanket thickness, debris caliber, and the
formation of case-hardened crusts. Stripping of an entire mantle is probably not
possible; however, materials trapped within
depressions form the only clearly discernible morphological expression of previously
more extensive debris blankets.
I
I
km
N
I
1
f
j
l
v
SYMBOLS:
Benchmarks
/--' Fault scarps, bar and ball
on downthrown side
~ Cracks
Conspicuous lava flows
0
INTRODUCTION
Burial of surface terrains by a friable
debris blanket and their subsequent exhumation may have been widespread on Mars
(Soderblom and others, 1973; Malin, 1976),
with important effects on the appearance of
features perceived from orbit. Martian
Figure 1. Sketch map of Kau Desert, Kilauea Volcano, Hawaii, showing five zones of
degradation of the 1790 tephra blanket. I. Complete cover by tephra. II. Areas of small
bedrock outcrops. III. Areas of continuous but fractional bedrock outcrop. IV. Bedrock
surface with small insets of debris. V. Bedrock and reworked accumulations and dunes.
Abbreviations: FPT = Footprint Trail, CP = Cone Peak, SH = Sand Hill, H = Halemaumau, HVO = Hawaiian Volcano Observatory, VH = Volcano House, KI = Kilauea Iki, K
Keanakakoi (pit crater), AK = Ahua Kamokukolau, MIT = Mauna Iki Trail.
Geological Society of America Bulletin, v. 94, p. 1148-1158, II figs., October 1983.
1148
I
STRIPPING OF TEPHRA, KILAUEA VOLCANO, HAWAII
91125
blanketing material may include weathering
products, rocks comminuted by meteorite
impact, and tephra that was formed by volcanic eruptions and emplaced (Binder and
others, 1977; Mutch and others, 1977) and
partly removed by wind (McCauley, 1973).
Objectives of the present study were (I) to
examine morphological characteristics of a
partly eroded tephra blanket on a fresh volcanic landscape, (2) to identify the erosional
processes, and (3) to determine the effects of
burial and exhumation on the surficial
appearance of the underlying lavas. Lavas
in the Kau Desert are primarily pahoehoe,
and so attention necessarily focuses upon
that type of surface, although tephra has
locally mantled aa lavas, and such relationships are treated briefly.
Setting
Kilauea is an active basaltic shield volcano constituting the southeast part of
Hawaii Island. Major orographic features
include the 3 by 5 km summit caldera
with its nested pit crater, Halemaumau,
and prominent east-west-trending and
southwest-trending radial rift zones. The
Kau Desert is a 350-km 2 wedge apexing at
Kilauea caldera with a longitudinal axis
along the Southwest Rift Zone (Fig. I). Surface materials are mostly thin, young basalt
flows, bedded tephra, and deposits of
reworked tephra debris.
A major phreatomagmatic eruption
within Kilauea caldera in 1790 A.D. distributed tephra over the Kau Desert,
creating the Keanakakoi Formation of
Wentworth (1938). A less violent phreatic
eruption within Halemaumau during 1924
formed a thin tephra layer at the caldera
rim. Reports concerning the 1790 eruption
consist of sketchy retrospective narratives
by natives as related to missionaries. An
eruptive column several kilometres high was
visible, and a group of Hawaiian warriors
were suffocated 9 km downwind from the
caldera. This tragedy and many charact&istics of the deposits have been interpreted to
support the hypothesis that base surge
played a significant role in emplacement of
Keanakakoi tephra (Swanson and Christiansen, 1973). Powers (1948) regarded only
the uppermost layers « I m) of the Keanakakoi Formation as a proQuct of the 1790
eruption, but Christiansen (1979) attributed
"
1149
the entire unit (> 5 m) to the 1790 event. His
interpretation was supported by recently
acquired 14C dates which indicated a basal
age younger than 350 ± 60 yr (Kelley and
others, 1979).
After nearly a century of lava-lake activity, Halemaumau erupted explosively on
May II, 1924, and continued to eject fragmental lithic material and copious steam for
14 days. During the peak of the 1924 eruption, rhythmic explosions ejected blocks
weighing several metric tons, ash-laden
steam clouds rose at least 2 km, and more
than 30 cm of lithic tephra accumulated
locally on the south rim of Halemaumau. A
few centimetres of finer lithic debris barely
cleared the southwest edge of Kilauea caldera (Powers, 1948, PI. 3D; Macdonald,
1949, p. 72; Macdonald and Abbott, 1970,
p. 315). An eyewitness account by Stearns
(1925) recorded a heavy fall of ash at
Pahala, 34 km southwest, and of sharp,
angular, sand-sized fragments, as large as I
mm, at nearby Wood Valley. Of especial
interest are showers of accretionary lapilli
(also called pisolites) reported by Stearns
(1925, p. 202), 2.5 km southwest of Halemaumau 2 hr after an explosion.
KEANAKAKOI TEPHRA BLANKET
Stratigraphy
Intermediate
Vitric
Unit
Lower
Mixed
Unit
Lava Flows
IWS
zones of
of small
Bedrock
Id dunes.
ialemaua Iki, K 0
[';-!',.,I
UC -
Pumice
o
I
2 meters
I
Unconformity
Figure 2. Simplified section of the three major units of the Keanakakoi Formation: an
upper lithic unit principally sand- to block-sized angular fragments of accessory rock, an
Intermediate vitric unit of silt- to sand-sized volcanic ash fragments (with minor amounts of
lithic, crystal, and pumiceous debris), and a lower mixed unit similarly composed of sandand silt-sized vitric, lithic, and crystalline materials. Unconformities between each unit.
Keanakakoi Formation consists of ash,
lapilli, and blocks of accessory material as
well as essential vitric ash and pumice
(Wentworth, 1938, p. 92-102). In Kau
Desert, this tephra blanket is heterogeneous,
although well stratified. R. L Christiansen
(U.S. Geological Survey, 1979, written
commun.) has studied in detail the stratigraphy, emplacement, mode of origin, and
age of these deposits. For our purposes, a
simplified threefold definition of the formation is adopted: (I) an upper, coarse lithic
unit; (2) an intermediate, finer, and richly
vitric unit; and (3) a lower, mostly fine,
mixed lithic and vitric unit (Fig. 2). The
upper unit is predominantly lithic, but
the intermediate and lower units contain
admixtures of vitric, lithic, and crystal
fragments.
Upper Lithic Unit. This is the most
distinctive unit of the three, ranging from
I mm to several metres thick and consisting
almost wholly of sand- to block-sized angular fragments of dense, nonvesicular accessory rocks, largely olivine basalt, picrite
basalt, diabase, and gabbro (Macdonald,
1949, p. 65). Scattered blocks as much as
&
1150
I m in size are seen near the caldera rim,
fragments of 20 to 40 em in diameter are
abundant within I km of the caldera rim,
and particles from 0.5 to 1.5 em prevail
throughout. This unit contains a few thin
(2-4 em) layers of brown, silt-sized fine volcanic ash locally rich in accretionary lapilli.
Bedding, although crude, irregular, and
discontinuous, is nonetheless prevailing.
Primary dips to 15° are abundant owing to
scour fillings and to draping over an irregular surface. Cross-bedding occurs in
some layers, on a 10- to 20-cm scale, and in
channel fillings near the caldera rim.
The upper lithic unit rests unconformably
upon the intermediate unit, as shown by
local angular truncation of bedding (Fig. 2).
Near the caldera rim, this contact is scoured
by U-shaped channels, many I m deep and 3
to 4 m wide. One 3-m-deep scour nearly cuts
thorugh the entire underlying section to
bedrock. Farther out in Kau Desert, thinness or absence of the intermediate unit
suggests considerable erosion before emplacement of the upper lithic unit.
The surface of the upper lithic unit has a
nearly ubiquitous case-hardened crust (Fig.
3) and a distinctive reddish-brown color
provided by a sand-silt matrix. Deposition
of mineral matter from drifting solfataric
fumes or from fluids sweated out of the
deposits is a likely cause of the crust.
Solfataric fumes, emanating from many
MALIN AND OTHERS
orifices around Kilauea, deposit sulfates
and opaline silica (Naughton and others,
1976), and similar substances might be
derived from seepage waters. Crust formation is a continuing process, for it occurs on
erosional facets of various ages cutting
across bedding and upon the walls of recent
gullies and cracks. A thinner, but somewhat
less coherent, crust has already developed
on 1924 tephra, indicating rapid formation.
Intermediate Vitric Unit. This unit can be
as much as 2 m thick near the caldera rim,
although extremely variable and sometimes
entirely missing. Fine grain size, high vitric
content, and a khaki brown color are characteristic. Fine lamination on a millimetre
scale is common, and layering is generally
well defined throughout. Coherent layers of
yellowish-brown, silt-sized fine ash (informally termed "mud") are generally thicker,
as much as 20 em, and more abundant than
in other parts of the Keanakakoi Formation. These thicker ashes are relatively massive and usually contain accretionary lapilli.
Scours 0.5 m deep within this unit occur
near the caldera rim, and there, at least, the
intermediate unit clearly lies upon a scoured
surface cut into the lower unit.
The intermediate unit contains lithic and
crystal fragments in addition to glass and
pumice. Although fine silt- and sand-sized
grains predominate, well-sorted layers, as
much as several centimetres thick, of clean,
loose, angular lithic fragments, for the most
part about 0.5 em in diameter, interrupt the
sequences of finer beds. Occasional lithic
blocks as large as 10 em are seen in such
layers. Pumice fragments, 0.5 to 2 em in
diameter, are particularly abundant in the
lower half of the intermediate unit, and
some layers as much as 10 em thick are
nearly pure pumice. The most obvious crystal fragments are olivine, although feldspar
also may be present.
In many exposures, the uppermost part
of the intermediate unit is a massive, yellowbrown, silt-sized fine ash, rich in accretionary lapilli in its uppermost part. Tracing 01
strata through the Kau Desert to the Footprint locality (Swanson and Christiansen.
1973), 9 km southwest of the caldera rim,
shows that the lower, desiccation-cracked,
"muddy" pisolitic layer, bearing fossil
human footprints, is this uppermost "mud"
of the intermediate unit.
Lower Mixed Unit. This unit is characterized by layers of relatively well sorted,
black, sand-sized coarse ash composed 01
angular lithic, vitric, and crystal fragments,
loosely packed and free running on exposed
faces. A few thin layers of yellow-brown
silt-sized fine ash interrupt the coarse I
ashes, and the unit is finer toward the bas,
of sections approaching 2 m in thickne"
near the caldera rim. Sections I to 1.5 111
thick, several kilometres southwest into
Kau Desert, are predominantly black, sand
sized coarse ash.
The top of the lower unit is marked by "
layer of shiny black, sand-sized coarse ash,
especially rich in large olivine fragmenh
Fragments of pumice, some as much as ;
em, are sparsely scattered throughout. Bcdo,
of coarser lithic fragments, chiefly vesicuJ;11
basalt as much as several centimetres IIi
diameter, are occasionally seen. Siderom,·
lane fragments are particularly abunda III
near the base, and some beds, several C,'li
timetres thick, are composed wholly of thl'
brownish glass.
I·
or1
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Ilr
IIII
Il. ~
lin
1111
. . w;
Ito
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ICll
>'111
.. lilt
"pr
ItlW
.111<1
hlTI
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IIlg
t·
1'17 _
hI'
I.,
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., Iso
lt,tI (
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General Relationships
li'lll(
'po
Figure 3. Case-hardened crust on upper lithic unit erodes to form a "scabby" appearance.
Some stones are firmly held in place by crust; others, loosened by disintegration of crust,
form lag gravel. Pocketknife (lower center) is 9 em long.
'III)
The existing integrated tephra blanket III
the Kau Desert covers approximately 'ill
km 2 , but remnant patches suggest an orii"
nal cover of at least 200 km 2 • The blanket"
coarsest and thickest near the caldera 11111.
exceeding 6 m on the southwest (KIIII
Desert) side and 10 m on the south rim Wnl
of Keanakakoi crater (Wentworth, I<)\S:
p. 93). The tephra blanket is elongated
southwestward, but a section reported to I"
tlC\l'1
,IIUI
"10,
!11lf'al
".1 \t'
',phr
(ldJilr
iil,III\'
j
STRIPPING OF TEPHRA, KILAUEA VOLCANO, HAWAII
for the most Pahoehoe
nterrupt the
lional lithic
~en in such
to 2 cm in
dant in the
: unit, and
1 thick are
lvious crysgh feldspar
Lower Tephra Units
Pahoehoe smooth and nonvesicular in some places,
but fractured or vesiculated in others.
Weathering produces surficial fracturing
and spalling that varies with flowage and
location and usually results in greater surface roughness, except insofar as ropy structures are removed by spalling. Aa bedrock
terrain is treated in a subsequent section.
Scabby Upland Terrain
o
rmost part
ve, yellowaccretionTracing of
, the Footristiansen,
Idera rim,
n-cracked,
ing fossil
ost "mud"
I
5m
I
Figure 4. Sketch illustrating onlap unconformity within tephra-filled swale on pahoehoe.
only 15 cm thick (Powers, 1948, p. 288) near
Cone Peak, 2 km southwest of the caldera
rim, is probably not representative, for sections 0.5 to 2 m thick were measured within
D.5 km east and west of Cone Peak. Local
Impressions of a thinner cover result from
character- an onlap unconformity of the upper lithic
II sorted, unit onto bedrock (Fig. 4). Excavations in
lposed of swales along Mauna Iki Trail, I km west
ragments, Irom Hilina Pali Road and 5.5 km southwcst of the caldera rim, reveal as much as
1 exposed
w-brown, D.5 m of tephra where surface exposures
: coarser suggest only a few centimetres, owing to the
the base onlap relationship.
The thickness of material removed from
thickness
to 1.5 m remnants of the tephra blanket is not
lest into k £lawn, but it was probably not great, conck, sand- Sidering the coarseness and coherence of the
upper lithic unit. Reworking of tephra
ked by a lower in the section during intervals within
and between eruptive episodes may have
arse ash,
heen more significant. Trade winds were
19ments.
lch as J lntainly competent to move freshly deposlied fine ash and pumice during and followut. Beds
1111(
eruptive episodes, and blasts generated
lesicular
hI' base surges (Swanson and Christiansen,
etres in
1'173) may have redistributed primary tephjeromeIii Contemporaneous fluvial transport was
)undant
,riso probably active, judging from torrenral cenllill downpours witnessed by Stearns (1925,
I of this
p 196) during the 1924 eruption.
Considerable dust probably has been
Irrl10ved from Kau Desert and largely
f ~ ported from the island. Stearns (1925, p.
10/ ) described dust clouds rising from the
nket in
.hert during and after the 1924 eruption,
tely 50
Mid similar events probably occurred in
10rigi
I7<lO. However, coarser materials contemmket"
I'olaneously reworked by the wind or by
ra rim,
"lise surges were not all removed from the
(Kau
Irpilra-mantled areas, as shown by sheets of
m west
rO/la n sand interlayered within primary
191h.
ngalcd , trpilra. At the Footprint locality, and in
j to I"
,it" farth" ,outhw"t, lay", of
l","
J 151
wind-blown sand approaching or exceeding
I m in thickness lie below, between, and
above the two "muddy," pisolitic fine ash
layers bearing fossil footprints (Powers,
1948, p. 289; Swanson and Christiansen,
1973, p. 86; Cruikshank, 1974, p. 226).
There seems little question that the pisolitic
ashes represent primary tephra, especially in
view of Stearns' (1925, p. 202) observation
of mud rains and pisolite falls in Kau Desert
during the 1924 eruption. Furthermore, a
thin layer of primary upper lithic material
overlies the uppermost footprint-bearing
bed.
One of the more distinctive and areally
extensive micro-terrain elements in Kau
Desert is formed by a durable, casehardened crust on the surface of the upper
lithic unit. Undermining of near-horizontal
resistant layers within this crusted surface
by weathering, wind, and water produces a
centimetre-scale, cliff-bench micro-topography of frayed and scabby appearance
(Fig. 3). Further small-scale surface roughness results from weathering, rain-beat, and
wind action, which etch angular rock fragments, firmly held in the crust, into positive
relief. Some stones rise on small pedestals I
or 2 cm high, and interstone areas are
pocked with hollows formed by weathering
and by removal of stones formerly embedded in the matrix.
Bedding-Plane Terrain
MICRO-TERRAIN ELEMENTS
Stripping of tephra from a subaerial surface is a function of time, initial thickness,
constitution (particularly particle size), induration, substrate configuration, and the
nature and power of the stripping processes.
Differential stripping of Keanakakoi tephra
from lavas in the Kau Desert since 1790 has
been controlled principally by thickness and
particle size, as demonstrated by the increased degree of stripping outward toward
the margins of the blanket where initial
thickness was least, and debris was finest.
The effects of stripping are conveniently
described in terms of resulting micro-terrain
elements, each displaying different but reasonably consistent characteristics. The following seven micro-terrain elements have
been defined within that part of the Kau
Desert formerly blanketed by the Keanakakoi Formation.
Bedrock (Pahoehoe)
This element has a gentle swell and swale
surface configuration, typically of I to 3 m
relief. Smaller-scale rolls, ropes, and festoons are usually present. The lava is
Small exposures of coherent sand- and
silt-sized ash layers of the intermediate and
lower Keanakakoi units are sparsely scattered through areas of extensively stripped
pahoehoe. Owing to draping in the lowermost layers, Wentworth's (1926, p. 25; 1938,
p. 30) "mantle bedding," bedding-plane
exposures are inclined in all directions at
angles approaching 15° and occasionally
attaining 28° . Cracks and small depressions
within ropes, festoons, and other irregularities of pahoehoe surfaces harbor deposits of
these materials. Nearly all exhumed rock
surfaces are stained a distinctive faint mustard brown.
Lag Gravel Terrain
Patches of residually accumulated pea- to
walnut-sized lithic fragments derived from
the upper lithic unit constitute an areally
significant and highly characteristic microterrain element. These gravels accumulate
in swales, pockets, and other low spots on
pahoehoe surfaces and on the upper lithic
unit (Fig. 5). Most patches attain several
metres in diameter, with a planimetric configuration reflecting the nature of the en-
..
•
1152
,.wi:4
Ii $
it ; a 2
]2
MALIN AND OTHERS
five zones of degradation displaying various
combinations of the seven micro-terrain
elements just described (Fig. I). Usually,
only three or four elements occur within a
single zone, but zone II, east of Cone Peak,
has six.
Zone I
Zone I consists of a nearly continuous,
surficially eroded tephra blanket forming a
band of 1.5 km wide immediately southwest
of Kilauea caldera. Topographically, this
zone features a broad surface sloping about
I ° southwestward, which is sparsely dissected by dendritic gullies as much as 4 m
deep and riven by open linear cracks of the
Southwest Rift Zone, bearing generally
S6QoW.
Figure 5. Lag gravel derived from upper lithic unit, capping finer tephra within swale in
pahoehoe. Abundance of pea- to walnut-sized fragments suggests significant removal of
fine material presumably by eolian processes.
closing depression: crudely circular or
oblate, elongated, or irregular. Individual
patches are more abundant than integrated
complexes. A flat-floored swale, enclosed
by swells of pahoehoe, with a discontinuous
border of upper lithic tephra around a central patch of residual gravel, is a common
arrangement. The gravel forms an armor of
single-stone thickness overlying as much as
50 em of fine primary tephra.
Fragments in gravel patches range from
scattered, with a remarkably uniform separation of 2 to 4 em, to densely packed, with
all fragments in contact or nearly so. An
impressive uniformity of particle size in a
patch may reflect a predominating size in
the parent material and sorting by the
transport mechanisms-impact creep, rainbeat, and sheet wash.
Colluvial Terrain
Colluvium forms on the walls of gullies
and cracks cutting through the tephra. It
consists principally of various grades of
sand from the intermediate and lower units.
Locally, cliffs in the upper lithic unit shed
coarse lithic fragments into the colluvium,
and cemented blocks of upper lithic beds
slump onto the colluvial slopes.
vious owing to crusting on the upper lithic
unit, thus allowing runoff. Segments of fluvial channels elsewhere extend for a limited
distance downslope from impervious areas,
chiefly bedrock. Most channel floors are
mantled by coarse fluvial sands and fine
gravels. Broad sand bars form where channels widen, and sand flats of many square
hectometres in extent occur where channels
debouch into areas of low relief.
Eolian Deposits Terrain
Deposits of wind-blown sand increase
outward within Kau Desert and become a
significant micro-terrain element near the
outer edge of the once tephra-blanketed
area. Minor leeside accumulations occur
throughout the desert, and larger deposits
have formed in the lee of major topographic
features-Cone Peak, for example-and
downwind from wide flats of fluvial sand.
Lithic, crystal, and vitric particles from the
intermediate and lower Keanakakoi units,
and Pele's hair from younger eruptions, are
the principal constituents of the eolian deposits, which are dark colored, well sorted,
and locally cross-bedded. The largest accumulations are dune ridges several metres
high, usually vegetated, and modified by
secondary blowout activity.
Fluvial Material Terrain
ZONES OF DEGRADATION
Fluvial channels are most abundant near
the caldera, where rainfall is greatest, the
Progressive deterioration of the Keana-
deposits are sufficiently thick to permit
kakoi tephra blanket southwestward from
channels, and the surface is most imper-
Kilauea caldera is treated by definition of
Micro-terrain elements distinguished
within zone I in order of decreasing area
are: (I) scabby upland, (2) lag gravel.
(3) fluvial deposits, (4) colluvial mantle, and
(5) bedrock. The predominating feature of
this zone is the cemented crust developed on
the upper lithic unit. It forms a broad.
gently sloping scab~y surface between rills.
gullies, and cracks and constitutes fully 90%
of the total area. This upland displays a gentle, irregular, swell and swale configuration
of about 0.5 m relief, presumably reflecting
the morphology of underlying pahoehoe
lava flows. A succession of crude wave-like
forms, with 15 to 20 m separation and 10 to
50 em amplitude, also ruffles the surface for
a few hundred metres outward from thc
caldera rim (Swanson and Christiansen.
1973). In the walls of cracks and gullies.
these waves are seen to consist of conformable accumulations of upper lithic materiaL
They are probably bed forms developed by
base surges.
Shallow swales and hollows scattered
over the upland are floored by accumulations of lag gravel, approaching desert
pavement in sorting and close packing 01
fragments. These accumulations are oncstone thick, with an infilling of youngcl
Pele's hair and other small vitric fragments
sifted downward between gravel fragments
Floors of fluvial washes are extensively
mantled by coarse sand and fine gravel
reworked from tephra. Colluvial material.
consisting of loose sand, lithic fragments.
and slumped slabs of well-cemented UppCI
lithic layers, mantles the steep walls of gullies and cracks below a topping cliff mad"
by the upper lithic unit. Bedrock constitutl',
only I% or 2% of the total area in zone I.
chiefly as narrow strips along cracks and
gully floors. At the caldera rim, a few knohs
I,
sa
$
"
1153
STRIPPING OF TEPHRA, KILAUEA VOLCANO, HAWAII
rious
:rraID
lally,
hin a
Peak,
IE i
f - Colluvium -7%
~gl
~
~~~~~
[2]
• ++ + + +
++++++
....
,-
Fluvial sand and gravel -5%
d - Lag gravel -8%
c _ Scabby upland of upper lithic
unit -65%
b _ Bedding - Planes of intermediate
and lower tephra units -3%
......
5~~-f;
ished
, area
ravel,
~, anel
lfe of
,ed on
,road,
I rills,
y90%
a gen:ation
o
0-
Bedrock (Pahoehoe) -12%
5
I
I
10m
I
Figure 6. Sketch distribution map and
section of micro-terrain elements within zone
II, near Cone Peak, Kau Desert. Fraction of
surface covered by each element given as
percentage.
~cting
ttereel
muladesert
ing 01
: onelunge I
ments
nents
Isively
gravel
tterial.
nents.
upper
)f gulmaele
titutes
.one I.
~s and
knohs
g-
';J..... t,...
<-( "- e- Pumice - Trace
uous,
ling a
ilwest
• this
tbout
, diss4 m
)f the
erally
oehoe
'e-like
10 to
ce for
n the
Insen,
ullies.
ormaterial.
led by
W~(~~:':1
of bedrock project through the western edge
of the tephra blanket.
I,one II
Zone II is the narrowest zone (0.5 km)
hut the most varied, containing the greatest
number of terrain elements (Fig. 6). It is
characterized by islands of bedrock, principally pahoehoe swells and tumuli, projectIIlg I to 3 m above a sea of tephra or
secondary debris. The dominant terrain
clement (40% to 50%) is the scabby upland,
like that of zone I. Along the east margin of
the tephra lobe in this zone, a loose lithic
j[ravel mantles as much as 65% of the surfilce. This gravel appears to be upper lithic
material, which escaped cementation, from
which the fine matrix has been driven by
wind, rain, and percolating water. Loose
!travel extends outward nearly to Ahua
Kamokukolau, 2 km southeast of the caldera rim, and makes up about 20% of the
total area of zone II (Fig. 7).
I.ocal bars and flats of fluvial sand and
gravel cover areas as large as several square
hectometres, and similar materials line
major fluvial channels. Lag gravel partly
covers the floors of most swales and hollows
on both the upper lithic unit and bedrock.
Bedrock, as irregular knobs or linear exposures along cracks and channels, makes up
as little as 10% to as much as 50% of the
surface. Bedding-plane outcrops of fine layers in lower Keanakakoi units and local
accumulations of wind-blown debris are the
remaining terrain elements.
Zone III
The tephra-bedrock pattern of zone III
reverses that of zone II. Here, residual
patches of tephra are scattered across an
integrated bedrock surface. One can walk a
continuous, albeit irregular, course wholly
on bedrock in zone III; in zone II, the continuous path is on tephra. Typical pahoehoe
swell and swale topography dominates.
Many swales are partly filled with tephra,
which outcrops peripherally around central
areas of surficial lag gravel. With the possible exception of ill-defined zone V, this is
the widest zone, at about 2.5 km.
Micro-terrain elements within zone III
are essentially those of zone II, but with different proportions. Zone III consists of 50%
or more exposed bedrock, approximately
25% residual gravel, 20% tephra, and 5%
fluvial sand and gravel. Residual patches of
the upper lithic unit resting directly on bedrock are abundant, and small exposures of
oxidized layers of lower Keanakakoi units
are also seen. Fluvial deposits are extensive
where streams from zone II debouch.
Downwind from such areas are small leeside accumulations of eolian origin.
Zone IV
Zone IV is the simplest zone, consisting
of 80% to 90% stripped lava that harbors
scattered remnants of tephra and of lag
gravel in swales and pockets. Small, scablike patches of the upper lithic unit (scabby
upland) remain on some lava swells, and
•
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1154
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MALIN AND OTHERS
thi
ne
~g-
Fluvial sand and
gravel 2%
IOoBI d -
Lag gravel 65%
sal
de
mt
gn
hri
up
eXI
Bedding-planes of
intermediate and lower
tephra units 20%
0-
res
be,
grc
del
Bedrock (Pahoehoe)
13%
A(
OF
I
o
I
5
1
10
I
Ke:
15m
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ily
Figure 7. Sketch distribution map
and section of micro-terrain elements
within zone II, near Ahua Kamokukolau. Fraction of surface covered by
each element given as percentage.
\Va
len
An
tephra layers (bedding-plane terrain) form
discontinuous marginal bands around flats
in secondarily filled swales (Fig. 8). Fluvial
sands line stream channels and locally form
more extensive bars and flats. Much of the
stripped pahoehoe in this zone displays a
faint yellowish-brown, oxide coating, inferred to have been imposed by tephra burial, as swales from which a tephra filling has
recently been partly removed show a "highwater" line of darker oxidation extending
to the upper level of the former filling.
Exposures of yellowish-brown, oxidized,
compact, sand-sized coarse ash beds of
lower tephra units are larger and more
abundant here than in zone III. Small
deposits of eolian sand occur mostly as
leeside accumulations.
KiL
and
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wat
Kil,
aha
Ilan
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Zone V
"I'W
Figure 8. Eroded swale filling of tephra, zone IV. about 6 km southwest of Kilauea
caldera. Zone IV. Resistant tephra layers ring accumulation of lag gravel.
Zone V is primarily an area of reaccumulation, displaying a pattern resembling that
of zone III with islands of bedrock rising
above a sea of predominantly reworked
materials. The primary tephra blanket (that
is, that emplaced directly by volcanic processes) was probably never thick here, and
much of the material filling swales and
creating dunes 3 to 4 m high is wind-blown
sand (that is, of secondary origin). Much of
Hail
III
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STRIPPING OF TEPHRA, KILAUEA VOLCANO, HAWAII
this sand was emplaced penecontemporaneously with the tephra. Deposits of fluvial
sand, approaching I m in thickness, are
clearly post-tephra. Bedrock constitutes as
much as 30% to 50% of the zone, and lag
gravels, fluvial sands, and wind-blown denris are abundant. A thin layer of granular
upper lithic tephra caps many of the tephra
exposures and also composes small scabs
resting directly on the bedrock. Vegetation
necomes more prevalent owing to favorable
growing conditions provided by finer
debris.
AGENTS AND PROCESSES
OF DEGRADATION
Principal processes involved in stripping
Keanakakoi tephra are wind-driven rain,
wind-driven sand, soil-water sapping, fluvlit! runoff, and particle creep (not necessarily in that order of effectiveness).
Water
form
flats
uvial
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-blown
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Kau is a desert more in the sense of barrenness than in that of lack of moisture.
Annual rainfall averages 130 cm near
Kilauea summit but diminishes to 30 cm
and less southwestward. Precipitation is not
particularly effective in supporting vegetalion or in causing fluvial erosion, owing to
venerally high permeability of the substrate.
Ivaporation is also high, because prevailing
northeast trade winds, having lost much
\\ater on the windward (northeast) side of
Kilauea, absorb moisture as they warm kat.Ihatically upon descending the southwest
llank of the volcano.
Much Kau Desert precipitation occurs as
Inlst and gentle drizzle, but torrential
dtlwnpours do take place. Most heavy pre'Ipitation is driven by strong winds from the
ntlrtheast (trades) or the south and southIITSt (storm-generated, "Kona" winds).
I II is makes rain-beat (Ellison, 1945) unusu,till' powerful and effective in this barren
legion. Testimony is provided by ubiquiIIIIIS earth fingers, 2 to 4 cm long, pointing
I1pwind in areas of soft, coherent sediment.
f(;lIn-beat may playa role in concentrating
"lllie fragments, 0.5 to I cm in diameter,
,!II tl lag gravel patches, and it probably con'flhutes to etching of the crusted upper
'lillie surface.
Ihe relatively impervious, almost ubiqui'<IllS crust on the upper lithic unit must
1'1 tlmote sheet flow during torrential rains.
\lIl'l"t flow can move loose debris lying on
"I <lad, unchanneled, gently sloping surfaces
1
that characterize much of the upper Kau
Desert.
Ephemeral streams clearly erode the
tephra. The nearly continuous blanket of
zone I is dissected by a system of dendritic,
ephemeral, rill, and stream channels. As this
is the area of heaviest rainfall, and 80% to
90% of the surface is crusted, the runoff is
great. Scattered larger channels, as much as
30 m wide, which have ~ut to bedrock, are
still, for the most part, too young to have
effected significant bedrock erosion, and
they are not likely to, owing to the permeability of the bedrock lavas. Areas formerly
blanketed by tephra probably also had an
integrated system of dendritic gullies and
rills, and at that time fluvial erosion was
more effective in removing tephra in those
areas than at present. As the tephra blanket
disintegrated, these gullies disappeared.
Soil-water sapping appears to be an effective erosive process in Kau Desert. Except
for crusted surfaces, infiltration capacity of
tephra materials is high, and even the crusts
are locally cracked, permitting some passage of water into underlying deposits.
These deposits contain pervious beds that
conduct water laterally, particularly where
interlayered with less pervious fines. Upon
emerging on a sloping face, this water
causes undermining and creation of escarpments of collapse. Steep walls of gullies
and cracks display steep-head amphitheaters, hanging tributaries, and waterfalls,
forms characteristically produced by seepage sapping. Sapping should be particularly
effective along the tephra-lava contact,
where the relative difference in permeability
concentrates percolating water.
Wind
Strong, northeasterly trade winds, occasional southwesterly storm winds, and lack
of sheltering by marked topographic relief
or dense vegetation favor eolian erosion in
Kau Desert. Dust storms rising from the
desert following the 1924 phreatic eruption
of Halemaumau demonstrated the efficacy
of eolian processes in removing fine material (Stearns and Clark, 1930, p. 59), and
sand dunes in southwest Kau Desert indicate effective eolian traction and saltation.
Impact by wind-blown, saltating sand
grains has probably played a significant role
in etching the surface of cemented crusts on
the upper lithic lay~r, and eolian undermining may have helped to create the scabby
upland microtopography of that unit. Wind
is the process most capable of removing fine
1155
tephra from closed depressions and, in the
absence of lateral erosion by streams, may
be a major means of removing such material
from wide, gently sloping interfluvial surfaces. After the upper lithic layer has been
breached, much of the underlying material
is susceptible to eolian entrainment.
Local granule ripples, composed of lithic
fragments as much as 4 mm in diameter,
demonstrate the ability of wind to move
coarse debris by saltation impact (Bagnold,
1941, p. 180), and lithic fragments in
patches of residual gravel may have been
moved down adjacent slopes by this process. Stable surface stones show modest
effects of sandblasting (polish, pitting, fluting) on their northeast sides.
Wind erosion presumably is less significant now than formerly, because material
susceptible to eolian entrainment is largely
gone, and much of the surface is protected
by crusts and lag gravels. Major currently
renewable sources of wind-blown sand are
the floors of fluvial washes and bars and
flats subject to flooding. These areas become armored within a few months when
subject to the current wind regime, but each
episode of flooding creates a new supply of
sand.
Mass Movements
The most obvious products of mass
movement within tephra-mantled areas are
slump blocks and tilted slabs of cemented
upper lithic layers on the walls of gullies and
cracks. The 5- to 15-mm lithic fragments,
composing lag-gravel patches, may move
downslope by particle creep, but this process is probably secondary to rain-beat and
saltation impact.
STRIPPING OF AA LAVA
Aa lava is less abundant than pahoehoe
in Kau Desert, but some opportunity exists
for comparison of stripping from these two
strikingly different surfaces. The roughness
and inhomogeneity of an aa surface obviously make stripping more difficult.
The penetrability of fine tephra into aa is
highly variable. Aa surfaces composed principally of pebble- to small cobble-sized
fragments can be sufficiently impenetrable
for a continuous mantle of fines to collect
and remain on its surface, but coarse,
blocky aa, just a few metres removed, may
merely appear to be unmantled, the material having penetrated into subsurface voids
between the large, angular, loosely packed
MALIN AND OTHERS
1156
Figure 9. "Gunite" tephra forcefully emplaced onto rough aa
lava, 3 km west of Kilauea caldera. Thickness and distribution
of coating on knobs suggest forceful emplacement from the
east-northeast, and adhesion suggests moist material.
o!
1m
I
blocks. Penetration may occur directly during initial emplacement of fine, dry tephra,
or it may be caused secondarily by rain-beat
and rain-water percolation. Although penetration probably should not be classed as a
form of stripping, its effect on surface
appearance can be similar.
Heavy rains (Stearns, 1925, p. 198, 200)
during the 1924 phreatic eruption suggest
that fine tephra may, on occasion, be
emplaced in a moist state. If it were wet
enough to form "mud," significant initial
penetration might not occur, even on
blocky surfaces. However, if water is in
excess, inwashing and penetration would be
expected. Coherent coatings of fine tephra,
many centimetres thick, adhering to nearvertical faces of bedrock knobs and cliffs
within aa flows near the northwest margin
of Kau Desert, indicate that fine tephra was
deposited there in a coherent, presumably
moist, state, allowing it to cling to steep
faces and to resist subsequent removal
(Fig. 9). These coatings resemble commer-
cial gunite, and their thicknesses and distribution on individual knobs suggest emplacement from an easterly or northeasterly
direction, possibly by trade winds or base
surges from Kilauea. Similar deposits were
reported in association with the Taal eruptions of 1965 (Moore, 1967). Sand-sized
tephra and accretionary lapilli, penetrating
deeply into niches and cavernous openings
with overhanging lips and tortuous configurations, suggest that forcible emplacement,
possibly by a base surge, was involved.
The surface rubble of aa flows is obviously highly pervious to water, with the
result that runoff from unmantled aa surfaces is essentially nil. This condition continues until subsurface interstices become
choked with fine debris. Channelized fluvial
erosion is thus both minimized and delayed.
The inhomogeneity of aa flows as to
penetrability, configuration, roughness, and
fragment size results in great differences in
stripping. To casual view, many areas of
coarse, blocky aa appear unmantled, al-
Figure 10. Zone II on aa. Scabs of crusted tephra form "flanges" around projecting
knobs of aa, featuring knobs of lava projecting through a blanket of tephra.
though adjacent to aa with tephra remnants. Only by standing on a high prominence and looking down upon the coarse
aa can one see that fine tephra chokes subsurface openings between blocks.
Blanketing and subsequent partial removal of tephra to a zone II condition on aa
results in numerous, randomly distributed,
small lava knobs projecting above an integrated surface of tephra and reworked deposits. One can easily walk between thesc
bedrock islands, remaining always on tephra materials. In aa of zone II, scabs 01
crusted tephra adhering to favorable sites
on rough lava knobs are modestly abundant, and crusted tephra also forms flanges
around the bases of the knobs (Fig. 10). Thc
filling in swales usually consists of a basal
section of primary tephra overlain by
reworked tephra debris, commonly lag
gravels underlain by finer sand and silt
derived largely from the matrix of the uppel
lithic unit.
A zone III aa development featurcs
separate pools and small irregular insets 01
tephra within an integrated lava surface
(Fig. I I). Infilled swales contain primary
tephra topped by a thick secondary layci
consisting of fine, massive, structureless
debris intimately penetrated by vegetatioll
rootlets. Lag gravels include some spalled
fragments and chips from surround in):
lavas, supplementing the usual upper lithic
unit particles. Scabs of cemented tephr<t
adhering to projecting lava knobs all"
smaller and less abundant than in a;1
zone II.
Arrangements comparable to pahoeho,'
zone IV (extensively stripped) exist onil
locally over small areas within an aa flo\\
They appear to be unmantled, but a vie\\
from above reveals an irregular infilling oj
fine tephra or secondary debris.
Tephra stripping processes are the same
as for pahoehoe, but differ in degree 01
effectiveness. Channeled fluvial runoff Oil
most aa is minor, but rain-beat and 10c;Ji
wash on mantled rock knobs must be firsl
rank. Mass movements, other than gravit\
induced creep of individual fragments Oil
slopes, are probably minor. Secondal \
penetration of fine debris into openings III
STRIPPING OF TEPHRA, KILAUEA VOLCANO, HAWAII
gh aa
Tephra Scabs
Filled swale
IItion
1157
n the
rem)rom:oarse
; subremoon aa
)uted,
I inte:d dethese
tephLbs of
e sites
abunlanges
I). The
, basal
m by
Iy lag
ld silt
: upper
:atures
lsets of
mrface
rimary
y layer
.ureless
etation
spalied
.unding
:r lithic
tephra
bs arc
in aa
.hoehoe
st only
La flow.
a vIew
illing 01
le same
:gree 01
noff on
ld local
be first
gravitytents on
condary
nmgs til
0
I
5
I
10m
I
Figure 11. Sketch offeatures within zone ilIon aa, showing separated insets of tephra within an otherwise continuous lava surface.
underlying rock is significant. Voids within
aa can become fully choked with fine material to depths approaching I m.
Wind is the only agent seemingly capable
of exporting tephra from aa. Its effectiveness is hampered through armoring by
coarse fragments, lack of saltating sand
grains to dislodge fine particles, and, ultimately, vegetation. It may be possible for
wind to remove some fine sand and dust
owing to wind turbulence generated by
increased surface roughness on aa flows. In
any case, sand does not travel far over aa by
saltation; it is too easily trapped in voids
and interstices. However, notable accumulations of eolian sand on aa occur near
places where wind has access to such a
copious source of material, such as fluvial
channels or flats, that sand floods the surface. The greater difficulty of stripping
tephra from aa, compared to pahoehoe,
produces about a one-zone difference on
adjoining areas of these lavas, with zone II
on aa lying alongside zone III on pahoehoe.
DISCUSSION
Stripping of the Keanakakoi tephra has
heen controlled by several factors: thickness
of the deposit, size of the component matertals, and relative effectiveness of erosional
processes. Areas farther from the vent
within Kilauea caldera received less material to begin with, and these thinner deposits
have been nearly totally removed. The size
of the component materials and the relative
effectiveness of stripping processes are in
~ome ways interrelated. In areas of fine
material, significant eolian deflation has
occurred; the absence of the intermediate
IIlld lower units of the Keanakakoi in distal
portions of the tephra blanket may reflect
early removal by eolian processes. Nearer
the caldera, where the upper lithic unit is
hoth coarser and thicker, finer debris is protected from wind action except where
exposed or eroded first by other, principally
fluvial, processes. Only water is capable of
moving the coarser lithic fraction of the
tephra; the absence of throughgoing drainage, owing to infiltration, modest precipitation, and high evaporation, restricts the
transportation of coarse material and allows the creation of residual concentrations
of pebbles and cobbles, as well as lag gravels. These "armors" can defeat further stripping. Intimately related to fluvial and eolian
action are the crusts formed on exposed surfaces of the Keanakakoi debris. The crust
on the upper lithic unit firmly holds many
coarse fragments and protects all underlying materials from erosion. It is this crust
that now dictates the rate and location of
erosion, by focusing water into a few channels (promoting fluvial erosion) and, by its
absence, permitting eolian action.
Two aspects of the morphology and planimetric configuration of the partly eroded
Keanakakoi tephra blanket are worth noting: the characterization of states of degradation by mixtures of micromorphological
criteria, and the potential time implications
of these spatial relationships. Of the seven
different micromorphological surface forms
used to characterize five zones of significant
difference, the occurrences of scabby upland, lag gravels, bedrock (pahoehoe or aa),
and bedding planes of lower units of the
Keanakakoi tephra are most diagnostic.
Bedrock is the principal element; the three
proximal zones can be said to consist of
"no" bedrock outcrop, "some" outcrop, and
"largely" bedrock. These zones are most
easily further divided by relationships of
mantling materials (primary tephra or secondary, reworked debris) to bedrock; the
variation from largely mantle surrounding
"islands" of bedrock to largely bedrock with
insets of mantle is the clearest change.
It is tempting, although perhaps not
appropriate, to associate time relationships
with the spatial relationships of zone
widths. Zone I, characterized by the thickest
deposits and most stable surfaces owing to
crusts, would appear to be the form originally taken by the deposit, and probably the
longest lasting, least affected. Zone II,
showing the onset of stripping as noted by
the increase in bedrock outcrop, may reflect
not only a thinner initial deposit, but also a
deposit at a later time in its evolution, when
erosional processes have breached the crust
and removed some but not all of the tephra.
Zone II is much narrower than zone III,
despite their morphologic kinship, and this
may reflect a more rapid evolution in time
from zone II to zone III than from zone I to
zone II (that is, little evolution occurs until
crusts are breached; then it proceeds rapidly
at first and then slows). Zone IV may
represent the final state, and one also longlived. Thus, the sequence of evolution may
be envisioned not only as a monotonic
decrease of thickness of deposit with time,
but also as a "wave" propagating from the
distal to the proximal deposits. With the
crusts acting to prevent significant lowering
of the present surfaces, it may be the case
that lateral erosion now is more important
than deposit thinning. Prior to the establishment of crusts and residual concentrations of stones, deposit thinning may have
been more important. The existence of dune
sands in zone V, interbedded with some
primary tephra, argues strongly for contemporaneous erosion and deposition. The
nature of the erosional processes, the time
scales over which they operated, the distribution of crusts, and the rate at which they
formed are thus critical to understanding
the early, postemplacement history of Keanakakoi tephra.
There are many ways in which the traditional erosional agents, water and wind, act
on the deposits in the Kau Desert. Water is
probably the most important agent, where it
can operate. It is restricted, however, by the
peculiarities of Kilauea hydrology. Inte-
aUUM
1158
grated drainages are found wholly and only
within the debris materials-no drainage
superposition onto underlying basaltic
flows occurs. Although alluvial deposits
have formed at the mouths of drainages,
these do not provide a substrate suitable for
further drainage development. Stream load
is limited to the few ephemeral streams and
is derived principally by bank scour, sapping, and mass movements. In-washing by
rainfall rather than stream flow is most
important in modifying tephra deposits on
aa flows, although this is not necessarily a
"stripping" process.
Wind is more effective over a wider area
than is water and, although limited by the
size of materials it can move, appears to
have played a significant role during at least
three periods in the evolution of the deposit.
Evidence in zones IV and V clearly points to
eolian processes active during eruptions and
during periods between eruptions. Today,
wind removes fine material from fluvial
deposits and continues to work surface
exposures of other loose materials.
The effects of burial on the bedrock itself
are also worth noting. A thick cover on
pahoehoe flows easily masks their already
subdued morphology. A thinner cover leads
to "islands" of bedrock (typically tumuli) in
a sea of flat surfaces, and a "totally"
stripped surface still retains as much as 20%
by area of primary and reworked debris, for
the most part filling depressions within the
pahoehoe flow surface. Bedrock so stripped
displays remarkably little physical evidence
of having once been buried. The principal
change, as viewed from above, is the
"mottled" appearance resulting from the insets of swale-filling mantle materials, often
surfaced by lag gravels with albedos that
differ from the pahoehoe flow. Morphology of pahoehoe flows is well preserved.
Aa flows show a different response to
burial. Although it is possible to mask an aa
flow by burial, the thickness must be great
because of the scale of morphology to be
covered. The topography on the surface of
an aa flow can be very complex, with ridges
and troughs several metres in relief, or it can
be relatively subdued, consisting of closely
packed, approximately spherical clinkers.
However, to mask an aa flow from view
requires that its flow margins be covered,
and this necessitates a thick deposit. For
thinner deposits, spines, boulders, and
ridges of aa clinkers may emerge upon
stripping. When they do, they may appear
more mantled than adjacent pahoehoe
flows, because of the difficulty in removing
material trapped within the greater surface
e
MALIN AND OTHERS
roughness of the aa flow. Without stream
drainage, and with infiltration and wind the
only effective transporting mechanisms,
material trapped on aa flows has a much
greater residence time. It is likely that an aa
flow retains most of a mantle, after it is
covered. However, owing to its initially
rough surface and steep margins, only a
thick deposit will create a significantly
altered view of the flow from an overhead
perspective. The difference between aa and
pahoehoe flows in retention of mantles, and
the ability to discriminate these mantles,
appear for the most part linked to the
planimetric scale of depressions upon their
surfaces.
Finally, there are the general implications
of these observations, and their importance
to places such as Mars, where observations
are necessarily limited to a distant view. It is
clear that mantles of debris, like the Keanakakoi tephra, can mask original morphology. The degree of masking, the relief of the
morphology, and the deposit thickness are
intimately related. Exhumed surfaces often
show only faint suggestions of prior burial,
principally in the form of lag gravels and
other materials too deeply intercalated
within surface depressions to be removed.
The stripping (or infiltration) of debris is
dependent upon the processes active, the
caliber of material that these processes can
move, and the size of the materials actually
available. In Hawaii, several processes have
worked in concert to create the surfaces
seen there. In the absence of significant fluvial action on Mars except, perhaps, early in
its history, critical factors concerning the
stripping of debris blankets are the caliber
of the debris; the effectiveness of other
mechanisms, principally wind, in transporting materials; and the detailed form
of morphological variations. Nonvisible
remote sensing, particularly Viking Orbiter
Infrared Thermal Mapper observations,
may address caliber (Christensen, 1982).
The effectiveness of wind transport can be
treated by laboratory simulation, theoretical modeling, and field study (Greeley and
others, 1982). Surface micromorphology
can be examined in Viking Lander images
(Mutch and others, 1977; Sharp and Malin,
1984) and compared with terrestrial analogues such as those presented here. The
synthesis of these diverse forms of study
with the high-resolution Viking Orbiter
images represents the most advanced stage
of analysis currently possible. The ultimate
test of the nature and evolution of martian
debris mantles likely will require in situ field
observations.
ACKNOWLEDGMENTS
We have benefited greatly from generous
discussions with R. L. Christiansen concerning his largely unpublished data on
stratigraphic characteristics of the Keanakokoi Formation. Personnel of the Hawaii
Volcano Observatory (USGS/HVO), too
numerous to specify, were most helpful.
This research was supported by funds
from the National Aeronautics and Space
Administration's Planetary Geology Program Office granted to the USGS/HVO
(Grant W 13.709), to the Jet Propulsion
Laboratory (where it represents one phase
of study carried out under NASA contract
NAS7-100), and to Arizona State University (Grant NAGW-I).
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london, Methuen and Company, 265 p.
Binder, A. B.. Arvidson. R. E.. Guinness. E. A., Jones K. L.. Morris.
E. C, Mutch. T. A.• Pieri. D. C, and Sagan, c., 1977, Th(
geology of the Viking Lander I site: Journal of Geophysical
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Christensen. P. R.. 1982. Martian dust mantling and surface composition: Interpretation of thermophysical properties: Journal 01
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Christiansen. R. l., 1979, Explosive eruption of Kilauea Volcano ill
1790 [abs.]: Hawaii Symposium on Intraplate Volcanism and
Submarine Volcanism, Hilo, HI. July 16-22, 1979, p. 158.
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MANllSCRIPT RECEIVED BV THE SOCIETV AUGUST
REVISED MANllSCRIPT RECEIVED SEPTEMBER
MANlJSCRIPT ACCEPTED OCTOBER 13, 1982
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