Quantitative morphology, recent evolution, and future activity of the
Kameni Islands volcano, Santorini, Greece
David M. Pyle*†
John R. Elliott†
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
ABSTRACT
Linking quantitative measurements of
lava flow surface morphology with historical observations of eruptions is an important,
but underexploited, route to understanding
eruptions of silicic magma. We present here
a new, high-resolution digital elevation model
(DEM) for the intracaldera Kameni Islands,
Santorini, Greece, which reveals the potential
of high-resolution imaging (at ~1 m per pixel)
of lava-flow fields by airborne light detection and ranging laser radar (LiDAR). The
new DEM has an order-of-magnitude better
resolution than earlier models, and reveals a
wealth of surface morphological information
on the dacite lava flows of the Kameni Islands.
In turn, this provides quantitative constraints
on the bulk rheology of the emplaced lava
flows. When combined with a reanalysis of
contemporary eruption accounts, these data
yield important insights into the behavior
of dacite magma during slow effusive eruptions on Santorini and elsewhere, and allow
the development of forecasts for the style and
duration of future eruptions.
Kameni Island lava flows exhibit classic
surface morphologies associated with viscous magma: levées and compression folds.
Levée heights and flow widths are consistent with a Bingham rheology, and lava
yield strengths of 3–7 × 104 Pa. Compression folds have long wavelengths (15–25 m),
and change only a little downstream; this is
consistent with observations of other terrestrial silicic lava flows. The blocky a‘a dacite
lava-flow margins show a scale-invariant
morphology with a typical fractal dimension that is indistinguishable from basaltic
Hawaiian a‘a, confirming that the fractal
*Corresponding author e-mail: dmp11@cam.
ac.uk.
†
Now at Department of Earth Sciences, University
of Oxford, Parks Road, Oxford OX1 3PR, UK.
dimension is insensitive to the composition
of the flow.
Dome-growth rates during eruptions of
the Kameni Islands in 1866 and 1939 are
consistent with a model of slow inflation of a
dome with a strong crust. Lava domes on the
Kameni Islands have a crustal yield strength
(4 × 107 Pa) that is lower by a factor of 2–4
than the domes at Pinatubo and Mount St.
Helens. The dome-height model combined
with the apparent time-predictable nature
of volcanic eruptions of the Kameni Islands
allow us to suggest that should an eruption
occur during 2006, it will last for more than
2.7 yr and produce a dome ~115–125 m high.
Keywords: digital elevation model, lava dome,
lava rheology, Aegean volcanic arc, dacite lava.
INTRODUCTION
A long-standing goal in volcanology is to
develop ways of extracting quantitative information about past eruptions that will allow us
to develop forecasts of the nature and timing of
future activity. In the case of lava flows, a key
area of investigation is understanding the relationship between the surface morphology of
lava flows, and the bulk dynamics of the erupting material (e.g., Hulme, 1974; Fink 1980; Kilburn, 2004). Understanding this link is critical
in general because of the importance of lava in
planetary resurfacing, and, specifically, because
it allows reconstruction of the detail of past
eruptions from the morphology of the emplaced
lavas, and underpins forecasts of how future
lava flows will evolve.
Here, we present a new high-resolution digital elevation model (DEM) for the volcanic
Kameni Islands (Santorini, Greece) based on a
light detection and ranging laser radar (LiDAR)
aerial survey carried out in April 2004. This is
one of the first applications of an aerial LiDAR
survey to a volcano, and the unprecedented
spatial resolution that the technique offers
opens up many new avenues for future work. In
particular, the new data reveal details of the surface morphology (on 1–100 m length-scales) of
young dacite lava flows, cones and domes, from
which important rheological information can
be extracted. In combination with a reanalysis
of historical eruption accounts, we show how
this information can be used to understand the
emplacement processes of viscous silicic lavas.
Santorini Volcano, Greece
Santorini is one of the active volcanoes of the
South Aegean volcanic arc. It has a rich volcanic history, with more than 12 major explosive
eruptions recognized over the past 250,000 yr
(Druitt et al., 1989, 1999). Typically, episodes
of caldera formation on Santorini have been
followed by extended periods of lava effusion,
leading to the intercalations of andesite to dacite
lava piles and andesite to rhyodacite tephra
formations that are exposed within the caldera
cliffs at the present day (Druitt et al., 1999).
Currently, Santorini volcano is in an effusive phase, with the focus of intracaldera volcanism for the past 2200 yr being the dacitic
Kameni Islands, which represent the emergent
top of a 2.5 km3 volcano that has a basal area of
~3.5 km2 and that rises 500 m from the floor of
the flooded caldera (Druitt et al., 1999). These
islands, of which there are currently two (Palea
and Nea Kameni, Fig. 1), have been the subjects of extensive petrological, geochemical,
and textural investigations over the past thirty
years because of their unusually uniform chemical compositions and their contrastingly heterogeneous population of exotic xenoliths and
cognate enclaves (e.g., Nicholls, 1971; Barton
and Huijsmans, 1986; Higgins 1996; Zellmer
et al., 2000; Holness et al., 2005; Martin et al.,
2006). There are considerable ongoing efforts to
characterize and monitor the state of the Kameni
Islands, in particular, the seismicity (Dimitriadis et al., 2005), hydrothermal and fumarolic
activity, and ground deformation (Stiros and
Geosphere; August 2006; v. 2; no. 5; p. 253–268; doi: 10.1130/GES00028.1; 16 figures, 9 tables, Data Repository 2006120.
For permission to copy, contact [email protected]
© 2006 Geological Society of America
253
Pyle and Elliott
20
25
30
Greece
40
40
N
Turkey
Colombos bank
Milos
Nisyros
Santorini
A
35
35
25
20
Colombos line
30
Megalo Vouno
Cape Colombos
Oia
Therasia
Cape Skaros
Thera
Fira
Nea Kameni
Figure 1. General location (A) and
geological map (B) of Santorini,
and the intracaldera Kameni
Islands, after Druitt et al. (1999)
and Martin et al. (2006). Part
A shows the shallow submarine
Colombos bank (NE of Santorini),
which was the location of an eruption in 1650 A.D., and the “Kameni
line,” which marks the NE-SW
trend of a region of preferred vent
locations on the Kameni Islands
(Druitt et al., 1989, 1999).
Kameni line
Palea Kameni
Profitis
Ilias
Akrotiri peninsula
Akrotiri
B
254
Second explosive cycle
2 km
Kameni volcano
Minoan tuff
First explosive cycle
Therasia dome complex
Cinder cones of Akrotiri peninsula
Skaros shield
Peristeria volcano
Cinder cones and tuff ring
Early centers of Akrotiri peninsula
Pyroclastic deposits
Basement
Geosphere, August 2006
Morphology of Kameni Island Lavas, Santorini, Greece
Chasapis, 2003; Vougioukalakis and Fytikas,
2005). Although the islands are currently in a
state of intereruptive repose, there is no reason
to suppose that there will not be future eruptions
of a similar nature, perhaps within decades, and
certainly within centuries.
Since the extensive work of Fouqué (1879),
Kténas (1926, 1927), Georgalas and Liatsikas (1925a, 1925b, 1936a, 1936b), and Reck
(1936a), which documented the course of many
of the historic eruptions in great detail (Table 1),
little attention has been paid to the physical form,
or posteruptive morphology and evolution, of the
lavas and ash cones that make up the Kameni
Island group. Indeed, many of these original
works have been overlooked, and the wealth of
relevant data they contain has been forgotten.
Historical Eruptions of the Kameni Islands
The historical activity of the Kameni Islands is
well known from contemporary written records
(Table 1). Modern compilations (e.g., Georgalas, 1962; Fytikas et al., 1990) generally begin
with the work of Fouqué (1879), who produced
one of the classic modern scientific accounts
of an active volcano and its evolution. Fouqué,
in turn, drew on material collated by Pègues
(1842), who published an extended account
of the historical activity of the islands, and by
Leycester (1851), who also published a detailed
bathymetric map of the caldera. The 1866–1870
eruptions were closely documented by Fouqué,
based in part on his own observations, as well
as on the many books and pamphlets that were
published within a year or two of the start of
the 1866 activity (e.g., Virlet d’Aoust, 1866;
von Seebach, 1867; Reiss and Stübel, 1868).
The 1866 eruptions clearly drew considerable
scientific interest at the time; for example, the
eruption was responsible for the earliest medical
work on the health effects of volcanic eruptions
(da Cologna, 1867). Together, the many published works that describe the major eruptions
of the eighteenth, nineteenth, and twentieth centuries present an excellent basis (Table 2) from
which to develop a quantitative analysis of the
evolution of an intracaldera volcano.
The salient features of the Kameni Islands
eruptions and their products are summarized
in Tables 1–4. The Kameni Islands make an
excellent case study since the eruptions have
exclusively involved dacite lava (Table 2), in
contrast to the many active lava-forming systems that have been studied in recent decades,
which are predominantly basaltic (e.g., Etna,
Hawaii; Walker, 1973; Pinkerton and Sparks,
1976). Eruptions typically include both domeforming and mildly explosive (Vulcanian)
phases, and the steady effusion of lava. During
the most closely observed eruptions of the twentieth century, flows typically extended to more
TABLE 1. HISTORICAL ACTIVITY OF THE KAMENI ISLANDS
Eruption date
10 January–2 February 1950
20 August 1939–early July 1941
23 January–17 March 1928
Location
References and notes
Nea Kameni
Nea Kameni
Nea Kameni
Georgalas (1953).
Georgalas and Papastamatiou (1951, 1953).
Kténas and Kokkoros (1929); Georgalas and
Liatsikas (1936b); Reck (1936c).
11 August 1925–January 1926
Nea Kameni
Kténas (1925a, 1925b, 1925c, 1926, 1927);
Washington (1926a, 1926b); Georgalas and
Liatsikas (1936a); Reck (1936b).
26 January 1866–15 October 1870
Nea Kameni
Described by Fouqué (1879); accounts of 1866
activity in von Fritsch et al. (1867) and Reiss and
Stübel (1868).
23 May 1707–14 September 1711
Nea Kameni
Described by Goree (1710) and Tarillon (1715a).
Eruption end date is from Tarillon (1715b);
misquoted as 11 September in Georgalas (1962)
and subsequent catalogues.
1570 or 1573
Mikra Kameni
The eruption was in either 1570 or 1573 (Fouqué,
1879).
1457
Palea Kameni
No eruption, but a collapse of part of Palea Kameni
(Fouqué, 1879).
726
Palea Kameni
Northeast side of Thia Island
46–47
Palea Kameni (Thia) Eruption of Thia, about 400 m from Hiera, to form an
island of ~5600 m circumference (Fouqué, 1879;
Stothers and Rampino, 1983). Now Palea Kameni.
19 A.D.
Thia
Reported by Pliny, but not regarded as an eruption
by later authors (e.g., Pègues, 1842; Fouqué,
1879).
199–197 B.C.
Hiera (or Lera)
Island that formed in 4 d, with a circumference of
2200 m (Stothers and Rampino, 1983). Presumed
to have been eroded below sea level. Fouqué
(1879) suggested Hiera was the Bancos reef,
which was northeast of Nea Kameni and was
covered with lava during the 1925–1926 eruption.
Geosphere, August 2006
than 500–1000 m over durations of 30–200 d
(e.g., Kténas, 1926; Georgalas and Papastamatiou, 1951, 1953; Georgalas, 1953), with flowfront advance rates ranging from 10−3 ms−1 in the
early stages to <10−4 ms−1 after 3 mo, and averaged effusion rates on the order of 0.5–2 m3s−1
(Fig. 2; Tables 3 and 4). The erupting lavas are,
therefore, classical examples of creeping viscous flows, with low Reynolds numbers (implying laminar flow) and moderate Peclet numbers, similar to those of slow-growing domes
(Griffiths, 2000).
DATA COLLECTION
Airborne data were collected over the
Kameni Islands, Santorini, in April 2004 during an overflight by the UK’s Natural Environment Research Council and airborne remotesensing facility (ARSF) Dornier 228 aircraft.
This aircraft was equipped with a WILD RC-10
camera, and Cambridge University’s Airborne
Laser Terrain Mapper (ALTM) system (Model
3033, Optech Inc., Canada). The aircraft survey
took place at an altitude of 650–780 m above
sea level (asl) and at a ground speed of 60–75
ms−1. The ALTM LiDAR was operated at 33.3
kHz and used a side-to-side scanning mechanism, which combined with the forward motion
of the aircraft to provide swath coverage of the
ground surface below. Data from an onboard
TABLE 2. TYPICAL FEATURES OF THE KAMENI
DACITE LAVAS
Parameter
SiO2 content
Inferred eruption temperature
Phenocryst content*
Inferred viscosity†, anhydrous
magma, η
Effective viscosity† of porphyritic
magma
Bulk lava density† (vesicle
free), ρ
Value
64–68 wt%
900–950 oC
15%
(4–6) × 104 Pas
(6–9) × 104 Pas
2680–2725 kgm–3
Flow characteristics
Typical flow rates§, V
Effective Reynolds number#, Re
Peclet number**, Pe
Prandtl number††, Pr
10–5–10–3 ms–1
10–5–10–3
2 × 102–2 × 104
2 × 107
*Phenocrysts (1–2 mm) of plagioclase and
clinopyroxene (Huijsmans, 1985; Higgins, 1996).
†
Viscosity and density calculated using Ken
Wohletz’s ‘Magma’ (http://www.ees1.lanl.gov/Wohletz/
Magma.htm), based on the Bottinga and Weill
(1972) model.
§
From field observations by Kténas (1926) and
Georgalas and Papastamatiou (1951, 1953).
#
Re = ρVh/η, assuming a typical flow depth, h, of
20 m.
**Pe = Vh/κ; κ, thermal diffusivity = ~10–6 m2s–1.
††
Pr = η/(ρκ)
255
Pyle and Elliott
TABLE 3. DEVELOPMENT OF EIGHTEENTH- AND NINETEENTH-CENTURY FLOW FIELDS
Eruption
Flow length
(m)
Lobe area
(km2)
Typical flow
thickness
(m)
Approximate
flow duration
(d)
Inferred
effusion rate
(m3s–1)
1200
1000
1200
0.9
0.2
1.7
> 30–60
20–50
30–70
300–600
90
600–1000
1–2
0.5–1.3
1–1.4
1707–1711*
1866†, Aphroessa flow (NNW lobe)
1866–1869†, Giorgios flows
*Accounts suggest that most lava extrusion occurred in 1707–1708 (Tarillon, 1715a, 1715b; Goree, 1710;
Fouqué, 1879).
†
See Fouqué (1879) and Georgalas (1962).
TABLE 4. DEVELOPMENT OF TWENTIETH-CENTURY FLOW FIELDS
Eruption
Maximum
length (m)
August 1925, N branch
Area
(km2)
Typical
thickness
(m)
Duration
(d)
Averaged
effusion rate
(m3s–1)
Data source
728
0.24
60
80
2.2
Kténas (1926)
August 1925, E branch
September 1939, NW and
SW lobes
1200
407–620
0.61
0.13
60
20–30
150
52
2.8
0.15–0.25
November 1939–April 1940,
N, E, SW lobes
320–620
0.38
20–30
95–230
0.4–0.7
Kténas (1926)
Georgalas and
Papastamatiou
(1951)
Georgalas and
Papastamatiou
(1953)
global positioning system (GPS) and the local
GPS base station (at Akrotiri) were used to
derive the precise flight path. First pulse and
last pulse data were recorded for each airborne
laser measurement and converted to location (x,
y, z) and intensity data by Gabriel Amable of
the Cambridge University Unit for Landscape
Modeling. During the overflight, 21 aerial photographs and 4.52 million light-imaging and
detection-ranging (LiDAR) measurements were
made. In addition, Airborne Thematic Mapper
(ATM) data were collected across 11 spectral
bands.
LiDAR
The processed LiDAR data comprised 4.52
million measurements over a surveyed area of
1200
10-3 ms-1
~8 km2, including a ground area of 3.86 km2.
Measured points have a nominal accuracy of
1.0 cm, 1.2 cm, and 5.9 cm in their x, y, and z
directions, respectively. The data were imported
into a geographic information system (GIS)
application (ARCMAP), and anomalous data
points (due to cloud cover) were removed. A
large area of absorption due to low cloud cover
appeared on one flight line (Fig. 3), so for this
area there is no precise height information.
Instead, this area was patched with a 15-m-resolution digital elevation model (DEM; from IntegralGIS). The LiDAR data were used to construct a high-resolution DEM by interpolating
the LiDAR points to an ~1 m post spacing using
a cubic spline function and fitting a surface to
these data.
A hill-shade rendition of the DEM is presented in Figure 4, and a contoured DEM is presented in Figure 5. In addition, maps of slope
(not shown) were generated to help visualize
surface morphological features. This digital
elevation model may be referenced either to the
UTM (Universal Transverse Mercator) grid, or
to standard latitude and longitude coordinates
(as shown in Figs. 3 and 4). It should prove a
useful starting point for any future analysis of
either pre-eruptive deformation of the Kameni
Islands or of posteruptive morphological evolution. For the present time, and the purposes of
this paper, the DEM allows us to proceed with a
detailed quantitative investigation of the surface
morphology of a number of key aspects of the
Kameni Island lava flows and domes.
1925 N branch
10-4 ms-1
1925 E branch
1000
August 1939 SW
Flow length (m)
August 1939 NW
November 1939 E branch
800
November 1939 SW branch
600
Figure 2. Flow lengths as a function of
time for the eruptions in 1925–1926 and
1939–1941, based on field maps and observations in Kténas (1926) and Georgalas and
Papastamatiou (1951, 1953). Time-averaged
flow rates typically range between 10−5 and
10−3 ms−1 (contoured).
400
200
0
1
10
100
Time elapsed (d)
256
Geosphere, August 2006
1000
Morphology of Kameni Island Lavas, Santorini, Greece
Aerial Photographs
Geological Map of the Kameni Islands
During the overflight, a set of 21 color analogue aerial photographs were captured using
the onboard Wild RC-10 camera. Together,
these images give a mosaic that covers the
entirety of the Kameni Islands. Images were
scanned digitally at high resolution, internally
referenced using fiducial points, and linked to
the x, y, z coordinates of identifiable ground
control points on the digital elevation model.
In turn, this allowed the photographs to be
corrected for distortion and terrain effects.
An orthorectified DEM-referenced aerial photograph mosaic is shown in Figure 6. This
image is complete, save for the easternmost
part of one lobe of the 1925 lava flow, which
was obscured by a cloud. This mosaic image
demonstrates clearly the ease with which the
surface textures of the lava flows and ash cones
can be identified, and with which flows of different age can be distinguished. We used the
aerial photographs, combined with the DEM,
in the following sections to develop an updated
interpretation of the geological map of the
Kameni Islands.
There have been several modern interpretations of the surface geology and eruption
sequence of the Kameni Islands, based primarily on the observations and interpretations of
Georgalas (1962). More recently, maps were
published by Pichler and Kussmaul (1980),
Huijsmans (1985), and Druitt et al. (1999). We
present an interpreted map in Figure 7, which
was prepared using a combination of feature
mapping (e.g., using the slopes visualized in
the DEM) and visual imagery. The new map
is properly georeferenced to the UTM and latitude-longitude grids, and is offset by 280 m (S)
and 225 m (W) from the UTM coordinates of
the Kameni Island map of Druitt et al. (1999).
The main difference in the new map, compared to that of Druitt et al. (1999), is the interpretation of the lava-flow sequence from the
1939–1941 eruptions in the western portion
of Nea Kameni. This is shown in the detail in
Figure 8A, along with extracts from two aerial
photographs of the same region: Figure 8B is
a monochrome photograph taken in May 1944
by a British reconnaissance aircraft, and Fig-
25°22'30"E
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ure 8C is the same view from the 2004 overflight. The new lava flows that erupted during
1939–1941 activity can be clearly seen in the
two photographs, as can the minor changes in
crater morphology associated with the 1950
eruption, and the emplacement of the very
small Liatskias dome and lavas, as described
by Georgalas (1953).
A second feature of the map is that, in contrast
to the earlier mapping of Pichler and Kussmaul
(1980), we see no evidence for exposed surficial
faults on Nea Kameni. In our map, we do not
explicitly identify the areas covered or partially
covered by younger ash deposits (e.g., the portions of the 1866–1870 lava flows covered with
ash from the 1925–1928, 1939–1941, and 1950
activity), but these areas can be identified from
the surface texture and coloration on the aerial
photograph mosaic.
Lava-Flow Surface Textures: Folding
The high-resolution DEM (Figs. 4 and 6)
reveals a wealth of lava-flow surface textural
information, most strikingly, the forms of lavaflow levées and fold patterns. Both of these
25°24'30"E
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Relative
laser
return
intensity
High : 1276
Low : -4
Figure 3. Light detection and
ranging laser radar (LiDAR)
return intensity map. Return
intensity is qualitatively related
to surface smoothness; there
are strong returns from the
old surfaces of Palea Kameni,
for example. The central strip
with no return intensity is the
flight line that was affected
by low cloud cover. The raw
LiDAR data (x, y, z, intensity)
are available in the GSA Data
Repository item accompanying
this paper (see text footnote 1).
Meters
2,000
Geosphere, August 2006
257
Pyle and Elliott
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m
2000
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25°23'45"E
25°24'0"E
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Figure 4. Hill-shaded digital
map of the Kameni Islands,
based on light detection and
ranging laser radar (LiDAR)
data. A coarse-resolution patch
(data provided by P. Moore,
IntegralGIS) was used to augment the missing strip. This
rendition clearly picks out surface morphological features
of the lava flows and domes,
including prominent levées and
lava channels. Note the contrast
between the rough surfaces of
the blocky a‘a dacite lava flows
and the smoother ash cones of
north-central Nea Kameni.
25°24'30"E
Coordinates are latitude longitude
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Elevation (m)
above sea level
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N
Sea level
0 - 10
10 - 20
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20 - 30
30 - 40
40 - 50
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m
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Geosphere, August 2006
25°24'30"E
60 - 70
70 - 80
80 - 90
90 - 100
100 - 110
110 - 120
Figure 5. Elevation map of the
Kameni Islands, shown as elevation above mean sea level.
Morphology of Kameni Island Lavas, Santorini, Greece
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sets of features, in principle, have scales that
are thought to reflect the rheological properties
of the underlying flow, and there are widely
used models for both approaches (e.g., levées:
Hulme, 1974; folds: Fink and Fletcher, 1978).
The resolution of the DEM (with a point spacing on the order of 1 m) means that the meterscale blocks that are often the most obvious
surface feature of these and other silicic lavas
in the field cannot be resolved.
One of the prominent features of the lavaflow morphology that is visible both from aerial
photographs and the DEM is the abundance
of gently arcuate ridges on the flow surfaces,
which are convex downstream (away from the
vent) and lie approximately perpendicular to
the flow direction. These ridges are best developed on flows (such as the 1707–1711 flow)
that also have well-defined levées. Ridges such
as these have been described from a number
of terrestrial and planetary volcanic settings
(e.g., Fink 1980; Gregg et al., 1998). Analogue
experiments, for example, using cooling wax
flows, strongly suggest that ridge development
happens early in the flow history as the flow
surface develops a crust (whether by cooling or
by crystallization; Griffiths et al., 2003). In the
case of the Kameni flows, field observations
25°23'30"E
25°23'45"E
25°24'0"E
25°24'15"E
25°24'30"E
Figure 6. Orthorectified aerial photograph mosaic of the
Kameni Islands, April 2004.
Particularly prominent features that can be seen include
the twentieth-century lava
flows (darker, rough surfaces
in the east and west of Nea
Kameni) and the discoloration,
due to persistent low-grade
fumarolic activity of the ashcovered regions of central Nea
Kameni. The modern tourist
trail that crosses the northern
part of Nea Kameni can also be
very clearly seen. The two small
islands that lie between Nea
Kameni and Palea Kameni are
the May islands, which erupted
in May 1866, and are now just
submerged. A high-resolution
version of this figure is available from the GSA Data Repository (see text footnote 1).
m
2000
show clearly that the ridges formed very close
to the vent, essentially as the lava flow was
extruded. In the case of the 1925–1926 eruptions, this much is also clear from the contemporary eruption reports (Kténas, 1926; Reck,
1936b). We quantify and interpret each of these
morphological features in subsequent sections.
Y = hgρ sin(α ) .
(1)
For a levée of width w, this is equivalent to
Y = 2ρgw sin 2 (α ) ,
(2)
while for a whole flow width of W,
Shapes of Lava Lobes: Levées and Folds
The shapes of lava flows, and the forms
of lava-flow fields, are complex functions
of the rheological properties of the fluid and
the emplacement conditions. It remains a
continuing goal of physical volcanologists
to understand and quantify these functions
(e.g., Griffiths, 2000; Blake and Bruno, 2000).
One widely used approximation of the behavior of viscous lavas is that they behave as
Bingham fluids, with a yield strength that must
be exceeded before flow can occur and a plastic
viscosity. Assuming a Bingham rheology, one
may use the widths of flows and the dimensions of their levées to gauge the apparent yield
strength of the fluid (Hulme, 1974; Hulme and
Fielder, 1977). For a flow of bulk density ρ and
depth h flowing down a slope of angle α, the
yield strength Y is
Geosphere, August 2006
Y=
ρgh 2 .
W
(3)
Dimensions of flow levées and surface folds
were determined by taking transverse and longitudinal (flow-parallel) sections across flows
(Table DR11). A typical cross-sectional profile
of a flow is shown in Figure 9. This exhibits
the classical form associated with a flow levée
(e.g., Sparks et al., 1976). Levées are typically
1
GSA Data Repository item 2006120, text file with
the raw LiDAR data (UTM coordinates, zone 35N),
a high-resolution aerial photomosaic of the Kameni
Islands, a table summarizing eruption volumes, and
figures showing the locations of sections used for flow
shape analysis, is available online at www.geosociety.
org/pubs/ft2006.htm, or on request from editing@
geosociety.org or Documents Secretary, GSA, P.O.
Box 9140, Boulder, CO 80301-9140, USA.
259
Pyle and Elliott
25°22'30"E
25°22'45"E
25°23'0"E
25°23'15"E
25°23'30"E
25°23'45"E
25°24'0"E
25°24'15"E
25°24'30"E
Lava dome
with crater
36°24'45"N
Nea Kameni
lavas
36°24'30"N
36°24'30"N
Mikra Kameni
lavas
Dafni lavas
36°24'45"N
N
Folds
Fissures
Levées
Liatsikas
dome
Fouqué, Reck
& Smith lavas
Niki lavas
Lava ages
1950
1940-1941
1939-1940
36°24'0"N
36°24'0"N
Agios Nikolaos
lavas
36°24'15"N
36°24'15"N
Kténas lavas
1939
1925-1928
36°23'45"N
1866-1870
36°23'45"N
Thia Lavas
Nea Kameni
0
250
25°22'45"E
500
1570-1573
726
46-47
Palea Kameni
25°22'30"E
1707-1711
25°23'0"E
1000
25°23'15"E
1500
25°23'30"E
25°23'45"E
25°24'0"E
25°24'15"E
25°24'30"E
m
2000
Figure 7. Interpreted geological map of the Kameni Islands, based on the new imagery and on previous maps compiled by Georgalas (1962),
Huijsmans (1985), and Druitt et al. (1999). The names of selected lava fields follow the conventions started by Fouqué (1879) and subsequent
authors (Georgalas, 1962). The Liatsikas dome is the youngest extrusive element on the Kameni Islands.
12–30 m high, 30–60 m wide (Table 5), with
outer slopes of 25–35°. While measurement
errors associated with the DEM are small, more
significant errors result from the subjectivity
of identifying levée margins, from the additional complications where levée dimensions
change downstream, or where flows bifurcate,
and from uncertainty in the slope down which
the flow was emplaced. The apparent viscosity
and yield-strength estimates based on lava-flow
morphology should only be regarded as orderof-magnitude estimates of flow parameters.
Estimates of yield strengths derived using
the three complementary approaches are summarized in Table 6. The yield-strength estimates derived from the gross-flow morphology
appear to be the most internally consistent and
suggest yield strengths on the order of 30 kPa
(1925 flows) to ~70 kPa (1940 flows). These
values are consistent with yield-strength estimates for dacites elsewhere (Hulme and Fielder,
1977; Wadge and Lopes, 1991). Yield-strength
estimates based on levée height are similar, in
terms of order of magnitude, to those based on
whole-flow morphology, while those based on
260
levée width are substantially smaller. The poor
agreement between the yield-strength estimates
based on levée width and those based on grossflow morphology is consistent with observations
elsewhere (e.g., Etna; Sparks et al., 1976) and
most likely reflects the fact that the processes
important in levée formation and evolution
(including accretion, avalanching, and cooling,
for example; Sparks et al., 1976) violate the
assumptions required for Hulme’s (1974) analysis to work.
In addition to the levées, another prominent
surface morphological feature of the Kameni
lava flows that can be seen clearly in the DEM
and aerial photo images is folding. A typical
longitudinal section along a flow, corrected for
the general slope of the flow field, is shown in
Figure 10. This shows folding with wavelengths
on a 10–100 m scale, defined by a train of arcuate ridges that runs perpendicular to flow direction. Folds of these sorts have been recognized
on a number of length scales on lava flows of
all compositions, from basalt to rhyolite, and
the usual interpretation is that they form as a
result of buckling of a more rigid surface layer
Geosphere, August 2006
(e.g., lava crust) during flow of the underlying fluid. Detailed descriptions and analyses
of examples of folding have been presented
by Fink and Fletcher (1978), Fink (1980), and
Gregg et al. (1998), among others; the motivation for this work, again, was the possibility
of inferring flow rheology and compositional
parameters for extraterrestrial examples (e.g.,
Warner and Gregg, 2003).
Nine lava flows were selected for surface
folding analysis, based on the visible ridges
seen in the DEM and aerial photographs. For
each flow, five parallel profiles, running perpendicular to the axis of the folds, spaced 2 m
apart, were taken along the middle sections of
each flow. Fold scales were investigated by fast
Fourier transform (FFT) analysis in MatLab
using a custom series of scripts to investigate
fold wavelength characteristics. Data were
prepared for FFT analysis by interpolating the
data to unit spacing, detrending the data stream,
and applying a cosine taper (Kanasevich, 1975;
Bracewell, 2000) to remove the baseline shift
and sinc convolutions, which would otherwise
have reduced the data quality. Typical examples
Morphology of Kameni Island Lavas, Santorini, Greece
356000
356500
Lava ages
4030500
4030500
355500
N
1950
1940-1941
1939-1940
1939
1925-1928
1866-1870
1707-1711
1570-1573
4030000
4030000
726
Lava domes
& craters
46-47
A
355500
356000
m
0
125
250
500
750
1000
356500
Coordinates in WGS84
UTM Zone 35N
B
of a contoured periodogram are shown in Figure 11, which shows the relative power (arbitrary scale) of fold wavelengths along the length
of a 1925 lava flow. This gives a rapid visual
assessment of the extent to which fold dimensions change, or otherwise, along a flow. In this
case, the fold wavelength is ~20 m close to the
vent and ~30–40 m further downstream.
Most of the flow profiles share a number of
common features: folds form close to the original eruptive vent. Folding is most prominent
close to the center-line of the flow, and in many
cases there is a consistent pattern of flow generations that develops downstream, i.e., several
fold generations of differing wavelength can be
recognized. Results are summarized in Table 7.
It is clear from Table 7 that most of the flows
that show folding have one generation of folds
with wavelengths (λ1) on the order of 15–25 m.
When multiple generations of folds exist, second-generation folds (λ2) have wavelengths
on the order of 25–65 m (or 1.5 ± 0.2λ1), and
third-generation folds have wavelengths of
30–110 m, or 1.8 ± 0.3λ2. This pattern of low
ratios (<2) between subsequent generations of
folds is consistent with the few data that exist
for other dacite (r = 2.1 ± 0.3) and rhyolite (1.8
± 0.4) flows (Gregg et al., 1998), and contrasts
strongly with the high ratios (5.1 ± 1.1) that
characterize basaltic flows (Gregg et al., 1998).
This confirms the potential of flow fold analysis for the identification of “silicic” flows by
remote sensing.
The scale of the folds qualitatively constrains
the minimum apparent viscosity of the underlying fluid (Fink, 1980; Gregg et al., 1998). Data
from the Kameni Island flows are consistent
with the view that in slow, effusive eruptions of
silicic magmas, crust formation on the flow by
cooling is much faster than crustal thickening
by strain, and consequently the folds that form
are of long wavelength. The slow effusion of the
flows is consistent with the observation that the
folds develop close to the vent.
Planform of Kameni Dacite Lava Flows
C
Figure 8. (A) Expanded map section showing the revised interpretation of the 1939–1941
lavas, with the inferred flow paths shown with arrows (+ symbols show the UTM grid intersections). The extracts from a 1944 Royal Air Force reconnaissance air photograph (TARA
ACIU 42090 3080) (B) and a 2004 air photo (C) show the subtle changes in the summit craters due to the minor explosive activity in 1950, and the emplacement of the Liatsikas dome.
Geosphere, August 2006
One motivation for the study of the quantitative morphology of terrestrial lava flows of
known composition is that it may reveal features that allow investigators to make inferences
about the compositions of flows on distant planets, simply from the remote observations of
morphology. One such approach that appears to
have some promise was proposed by Bruno et
al. (1992, 1994), which is to determine the fractal dimension, D, of the flow shape in planform.
The technique relies on measuring the gross
linear distance around an object as a function
of the length scale of the measuring rod. On a
261
Pyle and Elliott
75
X: 190
Y: 68.67
X: 96.65
Y: 68.23
70
X: 292.2
Y: 67.19
Height above geoid (sea level = 32 m above geoid)
Levée width = 79 m
65
Vertical exaggeration x6
Flow height = 35 m
60
Flow height = 36 m
55
50
Flow width = 331 m
45
40
Levée angle = 25°
35
30
X: 348.8
Y: 32.24
X: 17.77
Y: 31.9
0
50
100
150
200
250
300
350
400
Distance across levée (m)
Figure 9. Cross section showing a classical levée structure across the 1866 SW lava flow. Levées tend to be 15–30 m high, while flows are
100–300 m wide (Table 5).
TABLE 5. LEVÉE AND FLOW DIMENSIONS
Flow*
N†
Levée height
(m)
Levée width
(m)
Flow width
(m)
Surface slope§
(o)
1707
1866 SSW
1866 SW
1925 NE
1925 SE
1925 W
1940B
1940 SW
1940 W
16
2
5
4
3
5
5
12
4
23.1 ± 2.3
20.3 ± 2.0
25.2 ± 3.4
12.2 ± 1.5
18.8 ± 1.6
21.2 ± 3.5
18.0 ± 1.4
20.9 ± 2.1
16.4 ± 2.1
53.7 ± 6.6
32.9 ± 4.0
61.6 ± 5.5
29.5 ± 3.4
51.5 ± 1.6
39.4 ± 9.3
27.7 ± 1.8
44.9 ± 3.7
25.4 ± 3.3
224 ± 22
196 ± 17
310 ± 16
133 ± 4
201 ± 6
119 ± 12
121 ± 18
193 ± 13
103 ± 1.2
3.1 ± 0.7
4.3 ± 0.6
4.2 ± 0.5
1.5 ± 0.4
2.0 ± 0.2
0 ± 0.7
8.3 ± 2.0
2.6 ± 0.9
6.7 ± 1.0
*Sections across which measurements were taken are shown in Figure DR2 (see text footnote 1).
†
N—number of sections measured. Quoted error is the standard deviation of the measurements.
§
Slope is slope at present day. This may not have been the slope down which the flow was emplaced.
TABLE 6. YIELD STRENGTHS, ASSUMING BINGHAM RHEOLOGY
Yield strength
(×103 Pa)
Flow
1707
1866 SSW
1866 SW
1925 NE
1925 SE
1940B
1940 SW
1940 W
262
Flow width method
Levée width method
Levée height method
64 ± 14
57 ± 12
55 ± 15
30 ± 8
48 ± 8
72 ± 16
61 ± 13
71 ± 18
8±4
10 ± 3
18 ± 5
1.1 ± 0.6
3.4 ± 0.7
32 ± 15
5±3
19 ± 6
64 ± 6
75 ± 7
93 ± 13
23 ± 3
35 ± 3
134 ± 10
58 ± 6
107 ± 14
Geosphere, August 2006
log-log plot of distance versus length scale, data
following a fractal distribution should define a
trend with a linear slope of 1 – D. Bruno et al.
(1992) showed that the parameter varies with
lava type (a‘a versus pahoehoe) in basalts, but
also showed (Bruno et al., 1994) that many
more chemically evolved lavas do not show a
consistent fractal behavior.
The Kameni lavas present an excellent opportunity to test whether this model is applicable to
blocky dacite lavas.
Lava flows with well-defined margins were
digitized from the orthorectified aerial photographic images to obtain an outline with a spatial resolution of better than 1 m. Spatial data
were exported into a program (Fractals; http://
www.nsac.ns.ca/envsci/staff/vnams/Fractal.
htm; Nams, 1996) to determine the gross length
as a function of length scale, for length scales of
1–100 m. Most of the analyzed lava flows had
margins that could be traced for ~1 km, which
limited the upper range of length scale that could
be used. A typical plot of gross distance against
ruler length, confirming a fractal distribution,
is presented in Figure 12. All of the lava flows
that were analyzed showed clear evidence for
a fractal distribution, and, surprisingly, there
was no detectable difference between the fractal
Morphology of Kameni Island Lavas, Santorini, Greece
5
-2
dimensions of younger flows (<200 yr old) that
form the coastline and those with margins that
are entirely exposed inland. The only example
that was clearly nonfractal was the profile for the
A.D. 726 flow on Palea Kameni, which presumably has been deeply eroded. The fractal dimensions for all of the lava flows that were analyzed
are plotted in a histogram in Figure 13. It is clear
from this graph that the blocky a‘a dacite lavas
of the Kameni Islands have a fractal dimension,
D (1.067 ± 0.006, n = 10), that is indistinguishable from that of Hawaiian a‘a, at least on the
1–100 m scale. Thus, fractal dimension alone
may be a good discriminator for gross-flow type
(a‘a versus pahoehoe), but is not necessarily a
good discriminator for composition.
-3
Dome Growth on the Kameni Islands
4
Deviation in height from linear trend (m)
3
2
1
0
-1
-4
-5
100
200
300
400
500
600
700
800
900
1000
Figure 10. Surface buckling shown in a topographic section along the 1925 SE lava flow,
with the underlying slope removed. Note the prominent folding, which has 10–100-m-scale
wavelengths and 2–3 m amplitude. Data from flows are summarized in Table 7.
One typical feature of all of the historical
eruptions of the Kameni Islands is the growth
of lava domes. Field observations of the changing height of the summit of the 1866–1870
(Giorgios) dome and the 1939 (Fouqué) dome
were recorded, respectively, by Fouqué (1879),
and Georgalas and Papastamatiou (1953).
Figure 11. Contour map of the spectral power (arbitrary scale) of the different fold wavelengths in a set of five
parallel profiles, spaced 2 m apart,
along the length of the 1866 SW lava
flow. Window 1 is at the flow toe, and
11 is at the flow origin. Buckling with
an ~20 m wavelength can be observed
near the vent; downstream, a 30–40 m
wavelength becomes dominant.
Geosphere, August 2006
263
Pyle and Elliott
TABLE 7. WAVELENGTHS OF FOLDS
†
Flow*
N
Fold generation 1
(m)
Fold generation 2
(m)
Fold generation 3
(m)
1707
1866 SSW
1866 SW
1925 NE
1925 SE
1925 W
1940B
1940 SW
1940 W
21
11
11
21
21
11
11
11
11
19.9 ± 0.9
23.1 ± 0.4
23.5 ± 1.5
15.4 ± 1.1
26.0 ± 1.5
41.9 ± 1.7
21.5 ± 1.7
35.5 ± 2.2
38.5 ± 3.1
24.8 ± 0.9
32.7 ± 2.1
35.4 ± 1.0
21.0 ± 1.3
48.9 ± 2.0
63 ± 7
28.5 ± 1.1
48.8 ± 4.1
64 ± 6
35.5 ± 2.4
72 ± 5
28.4 ± 2.2
93 ± 19
53 ± 6
109 ± 12
*Sections along which measurements were made are shown in Figure DR1 (see text footnote 1).
†
Number of measurements
2.86
Log10 (gross distance, m)
2.84
2.82
.
Figure 12. Graph showing the relationship between the length of the measuring
rule (x axis) against the gross length of the
planform for the 1925 N flow. The data can
be described by a power law with a slope
of −0.054 (±0.001), which confirms that
the shape of the margin of this lava flow is
self-similar on a 1–100 m length scale (see
Mandelbrot, 1967). The data have a fractal
dimension of 1.054.
2.80
2.78
2.76
2.74
Caculated gross distance
Least squares regression line
2.72
95% prediction interval for a data point
2.70
0.0
0.2
0.6
0.4
0.8
1.0
1.2
1.6
1.8
2.0
Log10 (length scale, m)
14
Kameni blocky a'a
Galapagos a'a
Hawaii a'a
Hawaii
12
Number
10
8
Figure 13. Comparison of fractal dimensions determined for
Nea Kameni blocky a‘a flows with data from basaltic a‘a and
pahoehoe flows from Hawaii and Galapagos (Bruno et al., 1992,
1994). Fractal dimension appears to be an excellent discriminant of gross flow type, independent of composition.
6
4
2
0
1
1.04
1.08
1.12
1.16
1.2
1.24
D
264
Geosphere, August 2006
Morphology of Kameni Island Lavas, Santorini, Greece
TABLE 8. GROWTH OF DOMES DURING THE 1866 AND 1939 ERUPTIONS
1866 Giorgos Dome*
1939 Fouqué Dome†
Growth started 2 February 1866
Growth started 13 November 1939
Elapsed time
(d)
Dome height
(m)
Elapsed time
(d)
Dome height
(m)
20
30
50
50
70
108
118
3
7
9
28
65
150
23.5
30.5
40.5
45.5
56.5
78.5
3
5
35
47
108
396
1519
*1866 dome-growth parameters from Fouqué (1879).
1939 dome-growth parameters from Georgalas and Papastamatiou (1953).
†
1000
Kameni 1866 dome
Kameni 1939 dome
St. Vincent 1979
Mount St. Helens 1981 - 1986
Dome height (m)
Surprisingly, the importance (indeed, the
existence) of these data seems to have been
overlooked, and they are summarized for reference in Table 8. The dome-growth data are
plotted in Figure 14. Both dome-forming eruptions show closely similar growth rates in terms
of dome height (H) with time (t), which parallel those of the well-known lava domes of the
Soufrière volcano of St. Vincent (1979 eruption;
Huppert et al., 1982), and Mount St. Helens
(1980–1986; Swanson and Holcomb, 1990).
The power-law dependence of dome height with
time is close to the t1/4 dependence predicted by
models of domes that have growth controlled by
a crustal yield strength (e.g., Fink and Griffiths,
1998; Griffiths 2000), and the best-fit curve
with a t1/4 dependence is H = 1.2t1/4. Following Griffiths (2000), this suggests that the yield
strength of the crust of the Kameni dacite domes
is ~4 × 107 Pa, which is somewhat lower than for
the domes of St. Vincent (1.5 × 108 Pa), Mount
St. Helens (1.3 × 108 Pa), or Pinatubo (9 × 107
Pa; Griffiths, 2000).
It is worth noting that while the dome-height
data are consistent with a t1/4 time dependence,
alternative relationships cannot yet be ruled out.
For example, measurement errors are realistically likely to have been of the order of 1 m, and
the start time of the eruption (as opposed to the
time when magma emerged above sea level) is
not necessarily well known. In addition, Kameni
domes often show a transition from endogenous
growth early in the eruption, to modification
by Vulcanian explosions at later stages (e.g.,
Kténas, 1926). For these reasons, the possibility of a different time dependence (e.g., t1/3 for
a fixed dome shape and a uniform eruption rate)
cannot be ruled out; and in the event of a future
eruption, careful quantitative observations of
dome growth will be of great value.
The close similarity of the behavior of the
1866–1870 and 1939 domes allied with the uniformity of the composition of the Kameni Islands
over the past 2200 yr suggests that we may use the
heights of domes from earlier historic eruptions
to infer the eruption durations. We summarize the
results of this analysis in Table 9. The predictions
of both the t1/4 model and a time model based
simply on the empirical fit to the height data are
consistent with reports of these early eruptions.
Both models predict that the dome will grow to
a height of ~20 m within 1 d, and ~30 m within
4–5 d. Thus, for a submarine eruption originating
on the Kameni-Banco plateau (at ~20 m below
sea level), the dome should emerge above the surface within a day or two of the start of activity.
This is consistent with descriptions of the start of
the 1707 eruption (Goree, 1710; Tarillon, 1715a;
Fouqué, 1879). For domes emerging from this
submarine base level to the heights recorded in
100
10
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
Elapsed time (s)
Figure 14. Lava dome height (m) as a function of growth time, showing data from the 1866
and 1939 eruptions of the Kameni Islands (1866 Giorgios dome; 1939 Fouqué dome; Table 8),
the Soufrière volcano of St. Vincent eruption (1979; Huppert et al., 1982), and Mount St.
Helens (Swanson and Holcomb, 1990). The dependence of dome height on elapsed time for
the Kameni and other domes is close to t1/4, which is expected from analysis of domes with a
crustal yield strength (Fink and Griffiths, 1998; Griffiths, 2000). The solid line is the best-fit
curve through the Kameni data with t1/4 dependence: H = 1.217t1/4.
1875 of ~70 m (the 1573 dome), or 101 m (the
1707 dome), expected eruption durations are on
the order of 0.3–1 yr and 1–3 yr, respectively. The
latter is, again, consistent with the contemporary
records of the 1707–1711 eruption.
Simply on the basis of observed height of the
Mikra Kameni (1573) dome, it is plausible that
the eruption did indeed last for only 1 yr or less.
This supports our suggestion that the quoted
Geosphere, August 2006
TABLE 9. INFERRED ERUPTION LENGTHS
FROM DOME HEIGHT
Eruption
1573
1707–1711
Dome height above
base level
(m)
Inferred eruption
duration
(d)
70–90
134–368 (Griffith)
119–296 (Empirical)
560–1165 (Griffith)
433–835 (Empirical)
100–120
265
Pyle and Elliott
1570–1573 age range for this eruption derives
simply from an uncertainty in the calendrical date
of the eruption, and does not reflect the true duration of the event.
Apart from the anomalous event of 1950, all of
the historic intracaldera eruptions for which there
are at least adequate records (those since the
eighteenth century) have shared a number of
important common features: pre-eruptive uplift
of parts of the submarine Kameni edifice, and the
eruption of magma from at least two eruptive
vents. All have also involved the early formation
of lava domes, which later act as a focus for vigorous, intermittent explosive activity, as well as
acting as the vent from which lavas emerge.
There is no reason to suspect that a future eruption would not be preceded by the same general
phenomena—including general uplift of the edifice, and discoloration of the sea—and so, given
the current monitoring of the caldera, it is highly
likely that the next eruption will be anticipated
some days to weeks in advance. Some further
inferences about a future eruption on the Kameni
Islands can also be gained from a consideration
of the vent distribution and intereruptive periods.
Vent Distribution
The distribution of volcanic vents across the
Kameni Islands strongly suggests that there is
an underlying tectonic control on the supply of
magma toward the surface. As previous authors
(e.g., Fytikas et al., 1990; Druitt et al., 1989,
1999) noted, the vent pattern defines a narrow
NE-SW trend (Fig. 15) that extends northeast
of Nea Kameni to include the submarine high
(including the former Bancos bank), which
divides the flooded caldera basin into two parts.
Many of the prehistoric explosive eruptions also
have tephra dispersal patterns that are consistent
with vent locations along the same trend (Druitt
et al., 1989, 1999), and the locations of previous (pre-1866) and current hydrothermal vents
around the Kameni Islands also lie along this
same trend. Purely on the basis of the activity
of the past 1000 yr, one would anticipate that
the next intracaldera eruption would start in
the region between Palea Kameni (UTM zone
35N coordinates 40291, 3542) and northern Nea
Kameni (40302, 3568), and, as long as the eruption lasted more than 2 mo, it would involve two
or more eruptive vents.
Forecasting Future Events
The present state of the Kameni Islands can
most simply be interpreted as a part of the
266
Least squares regression line
4030600
Northing (m)
Future Activity of the Kameni Islands
Eruption vent location. Bars indicate approximate size.
95% confidence interval
4030100
4029600
4029100
4028600
354200
354700
355200
355700
356200
356700
Easting (m)
Figure 15. Graph showing the areal distribution of known vents from the Kameni Islands.
Error bars indicate the scale of the vent, crater, or dome. There is a very tight clustering of
vents about an approximately NE-SW trend, which agrees with the Kameni line identified
previously by Druitt et al. (1989). This trend is thought to mark the locus of a tectonically
(fault?) controlled magmatic plumbing system, and future activity is therefore likely to be
initiated at a point, or points, along the same trend.
intereruptive shield-building phase, which is
a typical feature of the evoluti on of Santorini
over the past 300,000 yr (e.g., Druitt et al.,
1999). Despite the considerable work that has
been completed on the dating of past eruptions of Santorini (Druitt et al., 1999), several
of the major explosive eruptions still lack a
good age control. Consequently, there are insufficient data from which to quantify the pattern
of intereruptive shield-building periods, for
example, using a rank-order approach (Pyle,
1998). Instead, we can use the known ages of
a few key eruptions to infer the mean interval
between all events. The last phases of seven
explosive eruptions were separated, on average, by 28 k.y. of repose. Within this sequence,
major lava shields were constructed between
ca. 67 and 55 ka (the Skaros shield) and ca. 50
and 21 ka (the Therasia dome complex; Druitt
et al., 1999). These crude constraints imply that
the shield-building phase might last for tens of
thousands of years. Assuming a mean interval
between explosive eruptions of 20–30 k.y., then
from Poisson statistics, there is a 50% probability that the post-Minoan shield-building phase
will last between 14 and 23 k.y.
Geosphere, August 2006
The relationship between eruption length and
intereruptive interval for the last 5 eruptions of
the Kameni Islands is shown in Figure 16. If we
regard the 1950 eruption as anomalously short,
and interpret this as a minor extrusion following the 1939–1942 activity, the notable feature
is that the remaining four events lie along a line
of best fit described by: eruption length (days)
= 7.4 × (intereruptive interval, yr) + 578. This
striking relationship is consistent with a model
for the Kameni Islands of a constant time-averaged deep supply of magma, and with eruption lengths that are determined by available
magma volume. Estimates of erupted volumes
(Table DR1, see footnote 1) are consistent
with this model; the largest recent eruption
(1866–1870) followed the longest pre-eruptive
repose period. If this empirical time-dependent
relationship holds in the future, then the next
Kameni Island eruption will last for more than
2.7 yr (in 2006) to more than 4 yr (in 2070).
CONCLUSIONS
A combination of high-resolution digital
mapping and aerial photography with archived
Morphology of Kameni Island Lavas, Santorini, Greece
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Eruption length (d)
2000
1600
1866
1707
1200
1925
800
1939
400
1950
0
0
50
100
150
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Intereruption interval (yr)
Figure 16. Relationship between eruption length and intereruptive interval for the last
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The dome-height model enables us to infer
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Kameni Islands. This, combined with the apparent time-predictable nature of volcanic eruptions
of the Kameni Islands since 1573 A.D., allows us
to suggest that the next eruption of the Kameni
Islands will last for more than 2.7 yr (in 2006) or
more than 4 yr (by 2070 A.D.), and may involve
the formation of a dome of ~115–125 m and
130–145 m height, respectively.
ACKNOWLEDGMENTS
Data were collected during the Natural Environment Research Council (NERC) Airborne Remote
Sensing Facility (ARSF) campaign to the eastern
Mediterranean in April 2004. Light detection and
ranging laser radar (LiDAR) data were expertly processed in Cambridge, Department of Geography Unit
for Landscape Modelling, by Gabriel Amable. We
thank David Cobby, Carl Joseph, Ivana Barisin, and
the ARSF team, and George Vougioukalakis (IGME),
Stathis Stiros, and Aris Chasapis for assistance with
data collection; and Vikki Martin for discussion. Pyle
thanks staff of the Earth Sciences and University
Libraries, Cambridge; the British Library; and Keele
University’s ‘Evidence in Camera’ for their able assistance with archive material. Elliott thanks Shell (UK)
for support toward field costs, and Zoë Rice for field
assistance. Part of this work formed John Elliott’s
final-year undergraduate dissertation. We thank Ricky
Herd and Steven Anderson for their detailed and helpful reviews.
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