Icarus 250 (2015) 18–31
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Icarus
journal homepage: www.elsevier.com/locate/icarus
Volcanism-induced, local wet-based glacial conditions recorded in the
Late Amazonian Arsia Mons tropical mountain glacier deposits
Kathleen E. Scanlon a,⇑, James W. Head a, David R. Marchant b
a
b
Department of Geological Sciences, Brown University, Providence, RI 02912, USA
Department of Earth and Environment, Boston University, Boston, MA 02215, USA
a r t i c l e
i n f o
Article history:
Received 26 August 2014
Revised 22 October 2014
Accepted 16 November 2014
Available online 22 November 2014
Keywords:
Mars
Mars, climate
Mars, surface
Volcanism
a b s t r a c t
The tropical mountain glacial fan-shaped deposit (FSD) to the northwest of the Arsia Mons volcano on
Mars contains numerous glacial and volcanic landforms. While most of the glacial landforms are
interpreted to have formed by cold-based glacial processes, several glacial landforms near glaciovolcanic
edifices are more consistent with localized wet-based glacial processes. These landforms include ribbed
moraines, which suggest local, thermal transitions between wet- and cold-based ice; thrust-block
moraines, whose formation is typically assisted by the presence of subglacial water; streamlined knobs
that we interpret to have been sculpted by ice sliding along its base; and a braided outflow channel.
The presence and association of these features, together with evidence of both subglacial volcanic eruptions and local ice-marginal advances, favor polythermal glaciers with localized wet-based conditions.
We propose that lava-to-ice heat transfer during the eruption of the glaciovolcanic edifices caused the
Arsia Mons paleoglacier to melt at its base in some areas, resulting in these locally wet-based glacial conditions. A polythermal glacier provides more potential microbial habitats and more connectivity between
habitats than does a cold-based glacier, and we review glacial and glaciovolcanic habitats on Earth that
may provide insight into the likelihood of potential microbial habitats within the Arsia Mons FSD on
Mars.
Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction
To the west or northwest of each of the Tharsis Montes lie arcuate deposits, delineated by concentric ridges, known as the lobe- or
fan-shaped deposits (e.g. Zimbelman and Edgett, 1992; Scott and
Zimbelman, 1995). While the fan-shaped deposits (FSDs) were initially interpreted as having formed by either mass-wasting processes, volcanic processes, or tectonic deformation (see review in
Shean et al., 2005), recent work (Head and Marchant, 2003;
Shean et al., 2005, 2007; Forget et al., 2006; Kadish et al., 2008;
Fastook et al., 2008; Scanlon et al., 2014) strongly supports the
hypothesis (Williams, 1978; Lucchitta, 1981) that the FSDs are glacial in origin. Specifically, the morphology of landforms in the FSDs
(Head and Marchant, 2003; Shean et al., 2005, 2007; Kadish et al.,
2008; Scanlon et al., 2014) strongly resemble, and show the same
spatial and stratigraphic relationships as, characteristic glacial
landforms deposited from cold-based ice on Earth (e.g. Atkins,
2013). The term ‘‘cold-based’’ refers to glaciers whose basal ice
temperatures are below the pressure melting point. Results from
Mars global climate models show that ice should accumulate on
⇑ Corresponding author.
http://dx.doi.org/10.1016/j.icarus.2014.11.016
0019-1035/Ó 2014 Elsevier Inc. All rights reserved.
the western flanks of the Tharsis Montes when martian spin-axis
obliquity is high (Forget et al., 2006), and output from coupled
ice-sheet climate models closely reproduce the footprints of the
deposits (Fastook et al., 2008). Three geomorphologic facies comprise the majority of the deposit at Arsia Mons: a Ridged, Knobby,
and Smooth Facies (Zimbelman and Edgett, 1992; Scott and
Zimbelman, 1995), interpreted, respectively, as drop moraines,
sublimation till, and remnant debris-covered glaciers (Head and
Marchant, 2003).
Like the other Tharsis Montes FSDs (Shean et al., 2005; Kadish
et al., 2008), the Arsia Mons fan-shaped deposit is associated with
landforms that have been interpreted as subglacially erupted volcanic edifices (Fig. 1). These landforms, outlined in black in Fig. 1,
include four plateaus interpreted as pillow mounds topped by
hyaloclastite mounds; a flat-topped, steep-sided plateau interpreted as a tuya; a steep-sided ridge interpreted as an ice-confined
lava flow; a series of digitate cliffs interpreted as ice-contact features; ridges grading into chains of pits, interpreted as eruptions
spanning the boundary between permeable and impermeable
ice; steep-sided, sunken-centered edifices interpreted as having
formed by lava extrusions that chilled at the margins but whose
still-molten centers receded into the vent; and numerous low,
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
steep-sided, areally extensive mounds interpreted as pillow
mounds (Scanlon et al., 2014).
Amazonian-aged relict glacial deposits, including concentric
crater fill, lobate debris aprons and lineated valley fill (e.g.
Squyres, 1979; Squyres and Carr, 1986; Mangold, 2003; Milliken
et al., 2003; Head et al., 2003; Garvin et al., 2006; Head et al.,
2006, 2010; Dickson et al. 2008) are found from polar to equatorial
regions of Mars. A lack of erosive features (e.g. grooves and molded
forms) or evidence for associated fluvial activity, however, suggests
that most of these deposits were formed by cold-based glaciers. In
the Noachian and Hesperian eras, there is evidence that ice sheets
at the south pole (e.g. Head and Pratt, 2001; Fastook et al., 2012), in
Valles Marineris (e.g. Gourronc et al., 2014), in Argyre basin (e.g.
Banks et al., 2009; Bernhardt et al., 2013), and in outflow channels
(e.g. Lucchitta et al., 1981) were wet-based, and that glaciofluvial
activity may have occurred in Gale crater in the Late Hesperian
or more recently (Fairén et al., 2014), but as the martian climate
became colder, cold-based glaciation became dominant. To our
knowledge, outside of the Tharsis Montes FSDs, all conclusively
Amazonian candidate polythermal or wet-based glacial deposits
proposed thus far have been restricted to small regions within
impact craters (Marchant et al., 2006; Hubbard et al., 2011), where
basal melting may have been assisted by remnant thermal gradients after impact (Marchant et al., 2006).
On Earth, heat transfer from intrusive or extrusive volcanism
underneath an otherwise cold-based ice sheet can be sufficient to
allow melting and locally uncouple the glacier from the ground
(e.g. Fahnestock et al., 2001; Fox Maule et al., 2005; Head and
Wilson, 2007; Hambrey et al., 2008). On Mars, fluvial outflow channels and aligned, streamlined knobs that have been interpreted as
drumlins in the Pavonis Mons fan-shaped deposit (Scott et al.,
19
1998; Shean et al., 2007) suggest that volcano–ice interactions
may have allowed local basal melting in the Pavonis tropical
mountain glacier, though it is unclear whether the stratigraphic
position of the streamlined knobs is consistent with the hypothesis
that they are drumlins. No evidence for fluvial flow or wet-based
glacial conditions has been documented, however, in the Olympus
Mons glacial deposits or the Ascraeus Mons FSD (Milkovich et al.,
2006; Kadish et al., 2008). In the Arsia Mons FSD, we find several
characteristic classes of wet-based glacial landforms. The spatial
relationships of these landforms to each other and to the documented glaciovolcanic edifices in the deposit suggest that the Arsia
glacier was locally wet-based (i.e., polythermal), with volcanism
rather than climate causing the wet-based conditions.
2. Data
Using ArcMap 10.0, we constructed a 5 m per pixel basemap
of all Reconnaissance Orbiter (MRO) Context Camera (CTX) images
(Malin et al., 2007) in the Arsia Mons fan-shaped deposit. Where
CTX coverage was absent or unclear, we consulted High Resolution
Stereo Camera (HRSC) images with 10–30 m per pixel resolution
(Neukum and Jaumann, 2004). The glacial debris and atmospheric
dust covering much of the Arsia Mons FSD obscure fine-scale features and dominate spectroscopic data, respectively, limiting the
usefulness of HiRISE and CRISM data in the vicinity of the landforms we describe here. We obtained topographic information
from 128 pixel per degree (463 m per pixel) resolution MOLA
(Zuber et al., 1992; Smith et al., 1999) data and HRSC-derived Digital Elevation Maps (DEMs) with 100 m per pixel resolution
(Dumke et al., 2008). These data were processed using the Spatial
Analyst toolkit in ArcMap 10.0.
Fig. 1. Geomorphological unit map of the Arsia Mons fan-shaped deposit (FSD), after Zimbelman and Edgett (1992) and Scott and Zimbelman (1995). Legend for color swaths
is provided in figure. Elsewhere, thin red lines denote large volcanic grabens, white lines denote contacts between units (dashed where inferred), and black lines denote the
outlines of glaciovolcanic landforms and modified moraine ridges. Blue and white dots in the smooth facies denote pits and knobs, respectively. THEMIS 100 m/pixel daytime
image mosaic; modified from Scanlon et al. (2014). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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3. Glacial landforms
3.1. Landform associations near the glaciovolcanic ‘‘Northwest
Plateau’’
A plateau towards the northwest of the Arsia Mons FSD (the
‘‘Northwest Plateau’’), first described by Wilson and Head (2007a,
2007b) and later by Scanlon et al. (2014), is interpreted to have
formed in a subglacial eruption (Fig. 2). The broad lower-elevation
mass of the plateau is interpreted as an effusive pillow eruption.
The steep, central mound superimposed upon it is interpreted in
Scanlon et al. (2014) to have formed in a later, explosive phase of
the eruption that began after subglacial meltwater drained from
the edge of the glacier and the ice above the vent melted and
thinned. Here we briefly review how this association of landforms,
described in greater detail by Scanlon et al. (2014), exemplifies the
interactions between glaciovolcanic activity and glacier thermal
regime recorded in the Arsia Mons FSD.
3.1.1. Observations
Directly downslope of the plateau, and in the inferred direction
of the paleo ice-surface slope, several shallow channels emerge
from underneath mounds of glacial debris and coalesce into a
braided channel 35 km long and 35 m deep where topographic
data is available. Between the plateau and the glacio-fluvial channels lies a field of knobs that are elongated and streamlined in the
downslope and inferred down-ice direction. Two sharp-crested
ridges, grading downslope to broad-crested ridges in the inferred
ice-flow direction, emerge from the steep upper mound of the plateau and superimpose the lower plateau. The long axes of the concentric ridges immediately downslope of the plateau are highly
arcuate in the inferred down-ice direction compared to nearby
members of the Ridged Facies. These ridges are superimposed
non-destructively upon other ridges with similar morphology
(Fig. 3), and are similar in size and shape to Ridged Facies members
at the same radius from Arsia Mons.
3.1.2. Evidence of wet-based glacial activity
On the basis of their braided planform and their emergence
from glacial debris, we have interpreted the braided channels
downslope of the Northwest Plateau as fluvial channels, indicating
the production and flow of a substantial volume of water at the
base of the glacier (Scanlon et al., 2014). The streamlined planform
and consistent northwest-to-southeast axis of elongation shared
by the field of elongated knobs suggests formation by local glacial
scour, possibly in a process analogous to the formation of terrestrial drumlins. On the basis of their morphology, size, and downslope transition from sharp-crested to broad-crested (consistent
with the expected behavior of subglacial channels with increasing
distance from a heat source; e.g. Shreve, 1985), Scanlon et al.
(2014) interpreted the sinuous ridges as accumulations of glaciofluvial debris (i.e. eskers), which are characteristic of wet-based
glacial environments. The non-destructive superimposition of the
arcuate ridges downslope of the plateau upon underlying features
and their morphological similarities to members of the Ridged
Facies suggest that the arcuate ridges, like the Ridged Facies ridges
(Head and Marchant, 2003), are drop moraines. The tighter radius
of curvature shown by the ridges downslope of the plateau, relative to nearby members of the Ridged Facies, suggests that they
were formed at the edges of a lobe of ice elongated in the same
direction implied by the other 3 landform classes, consistent with
a local increase in longitudinal ice-flow velocity and local icemargin advance (Fig. 4).
3.2. Ridges transverse to inferred glacial flow
The Lobate Facies (Zimbelman and Edgett, 1992; Fig. 1) is a unit
in the Arsia Mons FSD characterized by numerous, densely distributed steep-sided, lobate scarps and ridges, some of which grade
upslope into chains of pit craters. The steep-sided features are
interpreted as subglacial lava flows, and the pit craters as the sites
of phreatomagmatic eruptions under thinner ice, suggesting that
volcano–ice interactions were common in this region of the FSD
(Scanlon et al., 2014).
Fig. 2. The Northwest Plateau: (a) CTX image mosaic. (b) Sketch map. The Ridged Facies is shaded in red and the Knobby Facies is shaded in blue. Fluvial channels are denoted
by light blue lines and streamlined knobs are denoted by green lines. Boxed insets show the locations of Figs. 3 and 7. Modified from Scanlon et al. (2014). (For interpretation
of the references to color in this figure legend, the reader is referred to the web version of this article.)
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
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Fig. 3. Close view of drop moraines downslope of the Northwest Plateau. Drop moraines reflecting locally enhanced glacial flow (in the direction indicated by cyan arrow) are
non-erosively superimposed (red arrows) upon earlier drop moraines concentric with the boundaries of the Ridged Facies. CTX image P19_008605_1772_XI_02S129 W. (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3.2.1. Observations
At the contact between the Lobate and Knobby Facies (Fig. 5)
lies a 17 km wide field of sharply defined, commonly asymmetric,
regularly spaced, concentric or anastomosing ridges. The ridges are
oriented transverse to inferred ice-flow directions, and are up to
30 km long and typically 500 m to 1 km wide (Fig. 6). Where HRSC
DEM coverage is available, the ridges are typically 10–50 m high.
Smaller ridges (200 m wide and not high enough to be
resolved by the HRSC DEM), of similar shape and similar spacing
relative to their size, occur superimposed upon the Northwest
Plateau (Section 3.1; Fig. 7). The orientation of these ridges, southwest-to-northeast, is also transverse to the direction of inferred
glacial flow based on local topographic slopes and the landforms
described in Section 3.1.
3.2.2. Evidence of wet-based glacial activity
On the basis of their asymmetric and sharp-crested morphology, their concentric or branching arrangement, their regular size
and spacing, their orientation transverse to inferred paleo ice flow,
their alignment with moraines of unusual morphology farther
downslope (Section 3.3), and the fact that they do not appear to
gently drape underlying topography as do the drop moraines in
the Ridged Facies (Head and Marchant, 2003; Shean et al., 2007),
we interpret both the transverse ridges between the Lobate and
Knobby Facies and the transverse ridges superimposed on the
Northwest Plateau as ribbed moraines formed in association with
glacier ice that locally achieved wet-based conditions (cf. Dunlop
and Clark, 2006).
Ribbed moraines are unusual and complex glacial landforms.
They do not form alongside ice margins, but rather are produced
locally at the base of polythermal glaciers (e.g. Dunlop and Clark,
2006 and sources therein; Möller, 2006). The precise mechanism
by which they form is incompletely understood, but candidate origins include those in which (1) the moraines are the remnants of a
frozen till sheet that extends and fractures when a wet-based,
downslope region of a glacier flows more rapidly than a cold-based
interior region (Hättestrand and Kleman, 1999); (2) ice-cored
moraines left by a cold-based glacier are re-sculpted into ribbed
moraines when subsequently overrun by wet-based ice (Möller,
2006, 2010); (3) the crests of the moraines represent the crests
of former waves produced by a fluid dynamical instability in the
flow of glacial ice and subglacial till (Dunlop et al., 2008; Fowler,
2009; Chapwanya et al., 2011); or (4) moraines form when seasonal or climatic variations in subglacial meltwater content cause
the glacier bed to transition locally from an extensional to a compressional deformation regime (Lindén et al., 2008; Stokes et al.,
2008). Whether all subtypes of ribbed moraine form by the same
process is debated (e.g. Hättestrand and Kleman, 1999; Finlayson
and Bradwell, 2008; Lindén et al., 2008; Chapwanya et al., 2011),
but most researchers acknowledge that marked changes in horizontal ice-flow velocity, most easily accomplished beneath polythermal glaciers, are a crucial factor in their formation (Finlayson
and Bradwell, 2008).
We propose that the heat produced during episodes of extrusive
subglacial volcanism in the Lobate Facies led to basal meltwater
production, resulting in spatial and temporal gradients in basal
sliding and longitudinal ice-flow velocity (Fig. 8). These conditions
would have led to the development of the population of large
transverse ridges at the contact between the Lobate and Knobby
Facies by one of the formation mechanisms for ribbed moraines
discussed above.
We assert that the volcanic construction and subsequent
cooling of the Northwest Plateau affected the thermal regime of
adjacent glacier ice, producing polythermal conditions that led to
the development of the population of small ribbed moraines atop
the plateau. The superposition of ridges on top of the plateau suggests an origin via temporal, as well as spatial, transitions between
wet-based and cold-based ice conditions. Specifically, the ice
directly above the Northwest Plateau would have remained wetbased longer than the ice farther downslope from the volcanic heat
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Fig. 4. Map view of volcanic eruption (bright orange/gray) under ice sheet (white) on flank of volcano (dark brown), and resulting moraines (light brown lines): (a and b)
Local eruption generates heat and initiates ice acceleration and ice-margin advance. (c) As volcanism wanes, basal ice cools below the pressure melting point and subglacial
materials may be entrained; the entrained debris, as well as any previously deposited supraglacial debris, eventually falls passively at stationary ice margins, producing drop
moraines. (d and e) As the glacier recedes, drop moraines left behind will continue to delineate local still stands in overall ice recession. Based on variable ice margin
geometry, these superposed moraines may cross-cut, at oblique angles, drop moraines deposited during earlier times (Fig. 3). (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
source, causing compressive stress and ribbed moraine formation
above the plateau.
3.3. Enlarged, ridged moraine
At the northern edge of the FSD (Figs. 1 and 9) lies an L-shaped
ridge 50 km long, up to 450 m high, and up to 4 km wide. Due
to its height, steep sides, and the channeled morphology at its distal end, this ridge is interpreted to have formed as an ice-confined
volcanic flow; heat transfer from this volcanic flow to the surrounding ice is conservatively estimated to have generated
38 km3 of liquid water (Scanlon et al., 2014). Further upslope of
this ridge lies the glaciovolcanic Lobate Facies (Fig. 5). The morphology of the outermost moraine of the FSD in this region
suggests that the subglacial volcanism that formed the L-shaped
ridge and/or the Lobate Facies caused wet-based behavior in this
part of the paleoglacier.
3.3.1. Observations
Downslope and to the west of the ridge (Fig. 9), the terminal
moraine of the FSD differs dramatically in size and appearance
from elsewhere in the deposit (Fig. 10). The moraine is up to
3 km wide here, whereas it is typically only a few hundred meters
wide, and is taller here (up to 125 m) than elsewhere in the
deposit (Fig. 11). The moraine has several small parallel ridges at
its top and its MOLA profile resolves one broad ridge superimposed
on the moraine.
3.3.2. Evidence of wet-based glacial activity
Based on its size, surface appearance, and topographic profile,
as well as its exclusive occurrence downslope of the region of the
FSD containing the largest glaciovolcanic edifice and the highest
density of glaciovolcanic landforms, we interpret this feature as a
thrust-block moraine (also known as a composite moraine, or
sometimes as a push moraine; e.g. Benn and Evans, 2010). The
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
23
Fig. 5. Regional context map showing contacts between the Lobate, Ridged, and Knobby facies. The area shown in Fig. 6 is highlighted by a white box.
Fig. 6. Concentric, sharp, evenly spaced ridges, interpreted as ribbed moraines, at the contact between the Lobate Facies and the Knobby Facies (location indicated by white
box in Fig. 5). CTX image mosaic.
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K.E. Scanlon et al. / Icarus 250 (2015) 18–31
Fig. 7. Ridges interpreted as ribbed moraines (highlighted by white arrows) on the Northwest Plateau (location indicated in Fig. 2b). CTX image mosaic.
Fig. 8. Ribbed moraines may form where a glacier transitions from wet-based to
cold-based conditions, either over time or along a spatial gradient. The field of large
ribbed moraines in the Arsia Mons fan-shaped deposit may have formed where
subglacial eruptions in the Lobate Facies caused a transition from wet-based
conditions upglacier to cold-based conditions downglacier.
multi-ridged appearance (Fig. 10) and profile (Fig. 11a and b) of the
moraine is consistent with an imbricate stack of thrust slabs.
On Earth, such thrust-block moraines form where high longitudinal stresses act on weak subglacial sediments or bedrock, e.g.
adjacent to a steeply sloping ice margin or across a thermal boundary between wet-based and cold-based ice conditions. Basal debris,
entrained by regelation, may be advected upward along thrust
planes in the ice, potentially producing an imbricated moraine
ridge. Locally, elevated pore pressures that arise from permafrost-confined aquifers beneath polythermal glaciers may enhance
basal deformation and entrainment (e.g. Boulton et al., 1999;
Bennett, 2001; Benn and Evans, 2010), leading to the formation
of thrust-block moraines. In addition to being influenced by rheological properties of the deforming substrate, the size of thrustblock moraines scale with the magnitude and rate of glacial
advance (Bennett, 2001).
Within purely cold-based glaciers, thrust-block moraines have
only been documented where ice advances into marginal lakes,
where wet lacustrine sediment may freeze onto basal ice and move
upward along local thrust planes (Fitzsimons, 2003; Hambrey and
Fitzsimons, 2010); this process, however, is unlikely to have been
the case at Arsia Mons. Instead, we propose that the large moraine
ridge in the Arsia Mons FSD reflects polythermal thermal variation
near the ice margin. Local, wet-based conditions associated with
periods of subglacial volcanism were likely associated with basal
entrainment and increased sediment transport downglacier
(Fig. 12). As the ice flowed from the volcanic heat source it cooled,
and saturated basal debris would have frozen onto the cold ice;
compressive stresses near the ice margin could then have produced imbricate thrusts, bringing up frozen basal sediment and
producing the observed thrust-block moraine. This explanation is
bolstered by the fact that the hypothesized thrust-block moraine
lies directly downslope of a large field of ribbed moraines
(Section 3.3), which form directly over regions postulated to experience transitions from wet-based to cold-based glacier ice.
4. Discussion
Four characteristic classes of wet-based or polythermal glacial
landforms are observed near glaciovolcanic edifices in the Arsia
Mons FSD: (1) outflow channels, which record the release of large
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
25
Fig. 9. The L-shaped ridge and surrounding landforms. (a) THEMIS daytime IR image mosaic. (b) Sketch map of the region.
volumes of meltwater; (2) streamlined knobs, which record the
direction of glacial motion as well as its erosive power; (3) ribbed
moraines, which are thought to indicate transitions between wetbased and cold-based glacier ice; and (4) a large thrust-block moraine, which records the local deformation of basal sediment by
large glaciotectonic stresses typically associated with either fastflowing glacier ice (surging) or transitions from wet-based to
cold-based glacier ice. Together, the landforms provide a coherent
history at each glaciovolcanic site (Fig. 13): uniform ice-flow directions are recorded both by the streamlined knobs and the ribbed
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Fig. 10. Terminal moraine near the L-shaped ridge, showing ribbed surface appearance (red arrows). CTX image mosaic. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
moraines at the Northwest Plateau. Furthermore, the outflow
channels emerge directly beyond these landforms, as would be
expected if the enhanced flow was stimulated by wet-based conditions. Similarly, the ribbed moraines downslope of the numerous
glaciovolcanic edifices in the Lobate Facies and the thrust-block
moraine farther downslope at the terminus of the deposit both
point to a transition from wet-based to cold-based ice, which is
consistent with the placement of glaciovolcanic landforms in the
FSD (Fig. 13). These consistent landform associations imply that
glaciovolcanic activity was sufficient to alter the local thermal
regime of the Arsia Mons tropical mountain glacier, and their
exclusive association with glaciovolcanic edifices implies that climate and pressure effects were never by themselves sufficient to
cause basal melting in the glacier.
5. Potential microbial habitats in the Arsia Mons FSD
On Earth, glaciovolcanic environments provide a range of
microbial habitats (e.g. Cousins and Crawford, 2011). While the
chemical conditions would have differed from those in terrestrial
glaciers due to the lack of an oxygen atmosphere and a vigorous
biosphere, plausible redox couples and nutrient sources could have
made wet glacial environments on Mars hospitable to life (Cockell
et al., 2011). Since such environments would have originated from
volcano–ice interaction in the case of this deposit, volcanic gases in
some of the habitats would have further strengthened redox
gradients and provided an additional carbon source in the form
of volcanic CO2 (Skidmore, 2011). The Amazonian aqueous environments induced by glaciovolcanism may have been shorter-lived
than those arising due to impact heat in large craters (e.g. Abramov
and Kring, 2005; Barnhart et al., 2010). Taking the 102 m3 s1
effusion rates estimated for flows at Ascraeus Mons (Hiesinger
et al., 2007) as plausible rates for flows in the Arsia Mons FSD,
the volumes of FSD landforms like the Northwest Plateau and
L-shaped ridge (on the order of 1010 m3; Scanlon et al., 2014) suggest a duration of years to tens of years for edifice construction and
therefore at least that duration for wet-based conditions. Englacial
water bodies formed in response to these eruptions, however,
would likely have persisted for hundreds to thousands of years
before freezing (Scanlon et al., 2014).
The following environments, which geomorphological evidence
indicates were present in the Arsia Mons FSD paleoglacier, are
inhabited on Earth.
5.1. Englacial and basal lakes
The glaciovolcanic landforms in the Arsia Mons FSD are likely to
have generated several englacial lakes with volumes on the order
of tens of cubic kilometers and longevity of hundreds to thousands
of years (Scanlon et al., 2014). The few terrestrial volcanically generated englacial lakes whose ecosystems have been surveyed
(Gaidos et al., 2004, 2008; Marteinsson et al., 2013) contained
microbial communities capable of fixing carbon and nitrogen,
and including organisms related to known acetogens, sulfate
reducers and iron reducers. These communities are supported by
sediments and bottom waters rich in volcanic CO2, H2, ferric iron,
and sulfur compounds, as well as oxygen from the melted glacial
ice (Jóhannesson et al., 2007; Marteinsson et al., 2013).
At least one basal lake beneath 800 m thick ice in the Antarctic
Ice Sheet has been shown to host a microbial community supported by chemoautotrophic production (Christner et al., 2014).
Since the Arsia Mons paleoglacier experienced transient wet-based
conditions, analogous basal lakes within the FSD may have provided additional habitats for microbial life. Other ice-covered lakes,
such as those in the Antarctic Dry Valleys (e.g. Roberts et al., 2000;
Murray et al., 2012), are poorer analogs to the Arsia Mons lakes
because they originated as subaerial lakes. Subaerial lakes can be
colonized more easily than englacial lakes due to their exposure
to surface runoff and dormant, windborne microorganisms, and
after they develop an ice cover their productivity can still be
boosted by legacy carbon from the earlier lake ecosystem and
other nearby environments (Priscu et al., 1999).
Phylogenetic evidence suggests that the microbes that colonize
terrestrial subglacial volcanic lakes originate in a variety of other
environments, including glacial ice and snow, dust and marine
aerosols that work their way into the lakes long after being deposited on the glacier surface, drainage of surface meltwater into the
lake (Gaidos et al., 2004), or subsurface aquifers in contact with
the subglacial melt (Marteinsson et al., 2013). Neither surface runoff nor iced-over subaerial lakes are likely to have been present
near the subglacial lakes in the Arsia Mons FSD. The dike intrusions
in the Arsia Mons FSD could potentially have warmed the subsurface enough and melted enough ground ice for a liquid aquifer to
persist (e.g. Head and Wilson, 2002). Such an aquifer could have
hydrologically connected some habitats within the deposit,
enabling microorganisms to move between them. However, due
to the regional dust cover mantling the deposits, no spectral
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
27
Fig. 11. (a) Topographic profile across the line A–A0 in Fig. 9b, showing the increased height and ridged surface associated with inferred glaciotectonism. (b) Topographic
profile across the line B–B0 in Fig. 9b, showing the increased height and ridged surface associated with inferred glaciotectonism. (c) Topographic profile across the line C–C0 in
Fig. 9b, show a typical profile across the terminal moraine outside the region of wet-based glacial thrusting. Note the difference in y-axis scale between the three plots.
Topographic data from HRSC-derived DEM.
evidence for hydrothermal alteration minerals has yet been found
in the deposit, and any fine-scale morphologic features of hydrothermal systems would have been obscured by glacial debris in
the Ridged, Knobby and Smooth Facies. If circulating hydrothermal
fluid was not present, putative martian life could still have colonized the lakes if airborne propagules (perhaps the long-dormant
28
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
Fig. 12. We propose that the enlarged, ridged moraine at the northern edge of the
Arsia Mons FSD is a thrust-block moraine. This moraine could have formed when
proglacial or subglacial sediments were deformed by glacial thrusting, after stress
built up due to a wet-based region of the glacier lying upslope of a cold-based
region. The ribbed moraines located farther up ice (not shown) record a similar
arrangement of local wet-based conditions.
inhabitants of another transient surface habitat) worked their way
into the glacial ice, or if the ice itself was inhabited or contained
dormant life forms.
5.2. Wet-based glacier ice
While the Arsia Mons glacier was cold-based through much of
its spatial and temporal extent (Head and Marchant, 2003), we
have shown that subglacial eruptions induced local wet-based conditions in several regions of the Arsia Mons paleoglacier. Microbial
communities have been observed directly (e.g. by microscopy or
metagenomic analyses) or indirectly (e.g. by isotopic measurements) in the basal ice, water, brines, and sediments of wet-based
and polythermal glaciers in Alaska, Antarctica, Canada, Greenland,
New Zealand, and Norway (see review in Hodson et al., 2008). In
some cases these communities are more diverse than the surface
glacier communities (Hamilton et al., 2013). The environment
appears to support organisms that participate in iron and sulfur
cycling (Mikucki et al., 2004, 2009), methanogenesis (Stibal et al.,
2012a), and other processes that could have been viable on Mars.
Wet subglacial sediments in the Arsia Mons glacier could have
been inoculated by the same sources as subglacial lakes: groundwater connections, organisms in the ice, or organisms in surficial
or englacial debris.
5.3. Glacial ice and debris
The ubiquity of the Knobby Facies, which forms from the sublimation of debris-rich ice (Head and Marchant, 2003), indicates that
much of the Arsia Mons glacier was rich in debris. In terrestrial glaciers, debris-rich ice contains more microorganisms than clean ice
because the debris is a source of nutrients and electron donors or
acceptors. Furthermore, thin films of liquid water are present at
mineral–ice interfaces at temperatures well below freezing
(Wettlaufer, 1999; Price, 2007). Even when these films are too
small for microbes to move freely, dissolved ions and organic compounds are still mobile and allow microbes to carry out metabolic
processes including methanogenesis, denitrification, sulfate reduction, and iron reduction (see review in Price, 2007).
Clean ice can also contain habitable microenvironments at subfreezing temperatures. Small amounts of impurities (including
nutrients and organic compounds) have been shown to segregate
into veins between grains of ice due to their low solubility in solid
ice. These veins contain concentrated nutrients and are large
enough to allow microbes to move within them, and are thought
(Price, 2000) to be the reason viable microbes have often been isolated from ice cores (e.g. Christner et al., 2000). Organisms adapted
to subfreezing temperatures can survive, perhaps indefinitely
(Price, 2000), and even grow in these veins (Mader et al., 2006;
Dani et al., 2012).
While such environments are unlikely to be as productive as
macroscopic englacial water bodies, they may have represented
refugia from which these larger bodies could be colonized.
Remnant ice in the deposit (Head and Marchant, 2003; Shean
et al., 2007; Scanlon et al., in review), could provide these habitats
even today. Hollowed ridges at the western edge of the deposit
(Scanlon et al., in review), which have been interpreted to represent former snow dunes, indicate that snow or ice was transported
and reworked by wind in the region surrounding the deposit. This
would have helped disperse any ice-dwelling organisms, increasing the potential for colonization of any glacial or glaciovolcanic
habitats in the region.
5.4. Hyaloclastite and palagonite
While the subglacially erupted edifices in the deposit have not
yet been imaged with resolution high enough to identify surface
textures, and the material mantling the deposit may prevent confident identification even then, these structures should all contain
abundant basaltic glass due to the rapid chilling of basaltic lava
against ice as it erupted. We have argued (Scanlon et al., 2014) that
many of the landforms within the FSD should have glassy surfaces,
and that several should consist largely of rapidly quenched basaltic
tephra. Compared to crystalline basalt, hyaloclastite is a favorable
habitat for microbial life (as is its alteration product, palagonite)
because the lack of crystal structure makes nutrients in the rock
more easily accessible (Cockell et al., 2009). These basaltic glasses
are inhabited in exposed flows that were erupted subglacially, in
submarine lavas, and in subglacial lakes (e.g. Cockell et al., 2009;
Gaidos et al., 2004; Thorseth et al., 2001, respectively), and are
among the environments in which putative evidence of early terrestrial life has been found (Banerjee et al., 2006). The range of
autotrophic metabolisms supported by the volcanic glass environment on Earth remains incompletely characterized, however
(Cockell, 2011).
5.5. Biosignature preservation potential
In environments well-suited to the preservation of molecular
and morphological biosignatures, biogenic material is concentrated by physical processes, protected by rapid burial from oxidation and ultraviolet radiation at the surface, and isolated from
aqueous or thermal alteration after burial; ideally, phyllosilicates
are deposited simultaneously, aiding in preservation (Summons
et al., 2011). While spectrometers have thus far been unable to
conclusively determine the mineralogy of the region, several landforms in the deposit meet the other criteria.
The Northwest Plateau is one example of a location within the
FSD where biosignatures may have been generated and preserved.
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
29
Fig. 13. Summary schematic showing the relationship of inferred glaciovolcanic and wet-based/polythermal glacial landforms in the Arsia Mons FSD (not to scale). Right:
Enhanced ice flow and inferred polythermal conditions are recorded by ribbed moraines, streamlined knobs, and drop moraines that indicate a protruding lobe of ice centered
on the subglacially erupted Northwest Plateau; fluvial channels that emerge beyond this suite of basal deposits are consistent with this assertion. Left: In the northeastern
region of the FSD, the presence of numerous glaciovolcanic edifices upslope, ribbed moraine further downslope, and thrust-block moraine at the terminus of the deposit are
all consistent with a former transition from local wet-based conditions upglacier to cold-based conditions downglacier.
In terrestrial subglacial volcanic lakes, microbes are concentrated
in the hyaloclastite bottom sediments rather than in the water column (Gaidos et al., 2004). Any microorganisms inhabiting the
englacial lake above the Northwest Plateau would almost certainly
have been concentrated in the hyaloclastite for the same reasons.
Some of these sediments currently comprise the eskers extending
from the tephra mound; the top few meters of sediment in the larger esker would have easily been able to protect biogenic material
deeper in the esker against ionizing radiation (Kminek and Bada,
2006). The rest of the sediments are similarly protected by meters
of Knobby Facies material.
In addition to promoting redox gradients that support life, the
hydrothermal circulations present during the construction of subglacial edifices like the northwest plateau also promote the formation of sulfates and other minerals that can preserve chemical and
morphologic biosignatures (Cousins et al., 2013). Furthermore, the
knobby material itself is former englacial debris; as the Arsia Mons
glacier sublimed, any organic material that froze out of the water
column in the lake would ultimately be concentrated in the
Knobby Facies, along with material from habitats that may have
existed in the Arsia Mons glacier but are too small to detect by
remote sensing, such as the sub-meter-scale ‘‘cryoconite holes’’
melted into ice where low-albedo supraglacial debris aggregates
(e.g. Stibal et al., 2012b). There is no evidence to suggest that the
eskers, the central mound of the plateau, or the Knobby Facies have
been fluvially or thermally altered since their formation, except
possibly by the deposition of volcanic ash.
6. Conclusions
Glaciovolcanic landforms are abundant in the Arsia Mons fanshaped deposit. Previous work has made a strong case for coldbased glaciation at the Tharsis Montes, but new, higher-resolution
data show that landforms indicative of local wet-based conditions
due to interaction between lava and glacial ice are also distributed
throughout the deposit. These landforms, which record local
increases in ice-flow velocity and polythermal conditions, include
thrust-block moraines, ribbed moraines, highly arcuate drop moraines, streamlined knobs, and fluvial outflow channels. Since these
landforms all occur exclusively in association with glaciovolcanic
features, we conclude that the Arsia Mons FSD was left by a glacier
whose local wet-based conditions were induced by volcanic warming rather than by climate.
The aqueous environments evidenced by the Arsia Mons FSD
are exceptional in that they are comparable in size to similar
Noachian-Hesperian environments, and potentially much longerlived than other Amazonian environments. Furthermore, the Arsia
Mons glaciovolcanic environments occurred recently enough
(Kadish et al., 2014) that unambiguous molecular biomarkers have
been retrieved from much older terrestrial environments (e.g.
Brocks et al., 1999). If Mars Science Laboratory (Grotzinger et al.,
2012) or other upcoming missions discover evidence for fossil or
extant surface life on Mars, the Arsia Mons Fan-Shaped Deposit
would be a well-suited target for future human or robotic exploration to determine whether it persisted into the modern era.
Acknowledgments
We gratefully acknowledge support from the NASA Graduate
Student Researchers Program (Grant NNX12AI39H) to KES, from
the Mars Data Analysis Program (Grant NNX11AI81G) and the
Mars Express High-Resolution Stereo Camera (HRSC) Investigation
Team (JPL 1488322) to JWH, and from NSF Polar Programs (Grant
ANT-0944702) to DRM. We thank Alberto Fairén and an anonymous reviewer for constructive reviews that improved the quality
of the manuscript.
References
Abramov, O., Kring, D.A., 2005. Impact-induced hydrothermal activity on early
Mars. J. Geophys. Res.: Planets 110, E12S09.
Atkins, C.B. 2013. Geomorphological evidence of cold-based glacier activity in South
Victoria Land, Antarctica. In: Hambrey, M.J., Barker, P.F., Barrett, P.J., Bowman,
30
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
V., Davies, B., Smellie, J.L., Tranter, M. (Eds.), Antarctic Palaeoenvironments and
Earth-Surface Processes. Geological Society, London, Special Publications, 381,
pp. 299–318, http://dx.doi.org/10.1144/SP381.18 <published 24.07.13>.
Banerjee, N.R., Furnes, H., Muehlenbachs, K., Staudigel, H., de Wit, M., 2006.
Preservation of 3.4–3.5 Ga microbial biomarkers in pillow lavas and
hyaloclastites from the Barberton Greenstone Belt, South Africa. Earth Planet.
Sci. Lett. 241 (3–4), 707–722.
Banks, M.E. et al., 2009. An analysis of sinuous ridges in the southern Argyre
Planitia, Mars using HiRISE and CTX images and MOLA data. J. Geophys. Res.:
Planets 114 (E9), E09003.
Barnhart, C.J., Nimmo, F., Travis, B.J., 2010. Martian post-impact hydrothermal
systems incorporating freezing. Icarus 208 (1), 101–117.
Benn, D.I., Evans, D.J., 2010. Glaciers and Glaciation, second ed. Hodder Education,
p. 816.
Bennett, M.R., 2001. The morphology, structural evolution and significance of push
moraines. Earth Sci. Rev. 53 (3–4), 197–236.
Bernhardt, H., Hiesinger, H., Reiss, D., Ivanov, M., Erkeling, G., 2013. Putative eskers
and new insights into glacio-fluvial depositional settings in southern Argyre
Planitia, Mars. Planet. Space Sci. 85, 261–278.
Boulton, G.S., van der Meer, J.J.M., Beets, D.J., Hart, J.K., Ruegg, G.H.J., 1999. The
sedimentary and structural evolution of a recent push moraine complex:
Holmstrømbreen, Spitsbergen. Quatern. Sci. Rev. 18 (3), 339–371.
Brocks, J.J., Logan, G.A., Buick, R., Summons, R.E., 1999. Archean molecular fossils
and the early rise of eukaryotes. Science 285 (5430), 1033–1036.
Chapwanya, M., Clark, C.D., Fowler, A.C., 2011. Numerical computations of a
theoretical model of ribbed moraine formation. Earth Surf. Proc. Land. 36 (8),
1105–1112.
Christner, B.C., Mosley-Thompson, E., Thompson, L.G., Zagorodnov, V., Sandman, K.,
Reeve, J.N., 2000. Recovery and identification of viable bacteria immured in
glacial ice. Icarus 144, 479–485.
Christner, B.C. et al., 2014. A microbial ecosystem beneath the West Antarctic ice
sheet. Nature 512, 310–313.
Cockell, C.S., 2011. Life in the lithosphere, kinetics and the prospects for life
elsewhere. Philos. Trans. Royal Soc. A 369 (1936), 516–537.
Cockell, C.S. et al., 2009. Bacteria in weathered basaltic glass, Iceland. Geomicrobiol.
J. 26 (7), 491–507.
Cockell, C.S., Bagshaw, E., Balme, M., Doran, P., McKay, C.P., Miljkovic, K., Pearce, D.,
Siegert, M.J., Tranter, M., Voytek, M., 2011. Subglacial environments and the
search for life beyond the Earth. In: Siegert, M.J., Kennicutt, M.C., II,
Bindschadler, R.A. (Eds.), Antarctic Subglacial Aquatic Environments,
Geophysical Monograph Series, vol. 192. American Geophysical Union, pp.
129–148.
Cousins, C.R., Crawford, I.A., 2011. Volcano–ice interaction as a microbial habitat on
Earth and Mars. Astrobiology 11 (7), 695–710.
Cousins, C.R. et al., 2013. Glaciovolcanic hydrothermal environments in Iceland and
implications for their detection on Mars. J. Volcanol. Geoth. Res. 256, 61–77.
Dani, K.G.S., Mader, H.M., Wolff, E.W., Wadham, J.L., 2012. Modelling the liquid–
water vein system within polar ice sheets as a potential microbial habitat. Earth
Planet. Sci. Lett. 333, 238–249.
Dickson, J.L., Head, J.W., Marchant, D.R., 2008. Late Amazonian glaciation at the
dichotomy boundary on Mars: Evidence for glacial thickness maxima and
multiple glacial phases. Geology 36, 411–414.
Dumke, A., Spiegel, M., Schmidt, R., Neukum, G., 2008. High-resolution digital
terrain models and ortho-image mosaics of Mars: Generation on the basis of
Mars-Express HRSC data. In: Presented at Lunar and Planetary Science
Conference, XXXIX, Abstract #1910.
Dunlop, P., Clark, C.D., 2006. The morphological characteristics of ribbed moraine.
Quatern. Sci. Rev. 25 (13–14), 1668–1691.
Dunlop, P., Clark, C.D., Hindmarsh, R.C.A., 2008. Bed ribbing instability explanation:
Testing a numerical model of ribbed moraine formation arising from coupled
flow of ice and subglacial sediment. J. Geophys. Res.: Earth Surf. 113 (F03),
F03005.
Fahnestock, M., Abdalati, W., Joughin, I., Brozena, J., Gogineni, P., 2001. High
geothermal heat flow, basal melt, and the origin of rapid ice flow in Central
Greenland. Science 294 (5550), 2338–2342.
Fairén, A.G. et al., 2014. A cold hydrological system in Gale crater, Mars. Planet.
Space Sci. 93–94, 101–118.
Fastook, J.L., Head, J.W., Marchant, D.R., Forget, F., 2008. Tropical mountain glaciers
on Mars: Altitude-dependence of ice accumulation, accumulation conditions,
formation times, glacier dynamics, and implications for planetary spin-axis/
orbital history. Icarus 198 (2), 305–317.
Fastook, J.L., Head III, J.W., Marchant, D.R., Forget, F., Madeleine, J.-B., 2012. Early
Mars climate near the Noachian–Hesperian boundary: Independent evidence
for cold conditions from basal melting of the south polar ice sheet (Dorsa
Argentea Formation) and implications for valley network formation. Icarus 219,
25–40.
Finlayson, A.G., Bradwell, T., 2008. Morphological characteristics, formation and
glaciological significance of Rogen moraine in northern Scotland.
Geomorphology 101 (4), 607–617.
Fitzsimons, S.J., 2003. Ice-marginal terrestrial landsystems: Polar continental glacier
margins. In: Evans, D. (Ed.), Glacial Landsystems. Routledge, London.
Forget, F., Haberle, R., Montmessin, F., Levrard, B., Head, J., 2006. Formation of
glaciers on Mars by atmospheric precipitation at high obliquity. Science 311
(5759), 368–371.
Fowler, A.C., 2009. Instability modelling of drumlin formation incorporating leeside cavity growth. Proc. Royal Soc. A 465 (2109), 2681–2702.
Fox Maule, C., Purucker, M.E., Olsen, N., Mosegaard, K., 2005. Heat flux anomalies in
Antarctica revealed by satellite magnetic data. Science 309 (5733), 464–467.
Gaidos, E. et al., 2004. A viable microbial community in a subglacial volcanic crater
lake, Iceland. Astrobiology 4 (3), 327–344.
Gaidos, E. et al., 2008. An oligarchic microbial assemblage in the anoxic bottom
waters of a volcanic subglacial lake. ISME J. 3 (4), 486–497.
Garvin, J.B., Head, J.W., Marchant, D.R., Kreslavsky, M.A., 2006. High-latitude coldbased glacial deposits on Mars: Multiple superposed drop moraines in a crater
interior at 70°N latitude. Meteorit. Planet. Sci. 41 (10), 1659–1674.
Gourronc, M. et al., 2014. One million cubic kilometers of fossil ice in Valles
Marineris: Relicts of a 3.5 Gy old glacial landsystem along the martian equator.
Geomorphology 204, 235–255.
Grotzinger, J.P. et al., 2012. Mars science laboratory mission and science
investigation. Space Sci. Rev. 170, 5–56.
Hambrey, M.J., Fitzsimons, S.J., 2010. Development of sediment–landform
associations at cold glacier margins, Dry Valleys, Antarctica. Sedimentology
57 (3), 857–882.
Hambrey, M.J., Smellie, J.L., Nelson, A.E., Johnson, J.S., 2008. Late Cenozoic glacier–
volcano interaction on James Ross Island and adjacent areas, Antarctic
Peninsula region. Geol. Soc. Am. Bull. 120 (5–6), 709–731.
Hamilton, T.L., Peters, J.W., Skidmore, M.L., Boyd, E.S., 2013. Molecular evidence
for an active endogenous microbiome beneath glacial ice. ISME J. 7, 1402–
1412.
Hättestrand, C., Kleman, J., 1999. Ribbed moraine formation. Quatern. Sci. Rev. 18
(1), 43–61.
Head, J.W., Marchant, D.R., 2003. Cold-based mountain glaciers on Mars: Western
Arsia Mons. Geology 31 (7), 641–644.
Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003.
Recent ice ages on Mars. Nature 426, 797–802.
Head, J.W., Pratt, S.F., 2001. Extensive Hesperian-aged south polar ice sheet on
Mars: Evidence for massive melting and retreat, and lateral flow and ponding of
meltwater. J. Geophys. Res.: Planets 106 (E6), 12275–12299.
Head, J.W., Wilson, L., 2002. Mars: A review and synthesis of general environments
and geological settings of magma–H2O interactions. In: Smellie, J.L., Chapman,
M.G. (Eds.), Volcano–Ice Interaction on Earth and Mars. Geological Society,
London, Special Publication, The Geological Society of London, London.
Head, J.W., Wilson, L., 2007. Heat transfer in volcanoice interactions on Mars:
Synthesis of environments and implications for processes and landforms. Ann.
Glaciol. 45 (1), 1–13.
Head, J.W., Marchant, D.R., Agnew, M.C., Fassett, C.I., Kreslavsky, M.A., 2006.
Extensive valley glacier deposits in the northern mid-latitudes of Mars:
Evidence for Late Amazonian obliquity-driven climate change. Earth Planet.
Sci. Lett. 241, 663–671.
Head, J.W., Marchant, D.R., Dickson, J.L., Kress, A.M., Baker, D.M.H., 2010. Northern
mid-latitude glaciation in the Late Amazonian period of Mars: Criteria for the
recognition of debris-covered glacier and valley glacier landsystem deposits.
Earth Planet. Sci. Lett. 294, 306–320.
Hiesinger, H., Head III, J.W., Neukum, G., 2007. Young lava flows on the eastern flank
of Ascraeus Mons: Rheological properties derived from High Resolution Stereo
Camera (HRSC) images and Mars Orbiter Laser Altimeter (MOLA) data. J.
Geophys. Res.: Planets 112, E05011.
Hodson, A. et al., 2008. Glacial ecosystems. Ecol. Monogr. 78 (1), 41–67.
Hubbard, B., Milliken, R.E., Kargel, J.S., Limaye, A., Souness, C., 2011.
Geomorphological characterisation and interpretation of a mid-latitude
glacier-like form: Hellas Planitia, Mars. Icarus 211 (1), 330–346.
Jóhannesson, T., Thorsteinsson, T., Stefánsson, A., Gaidos, E.J., Einarsson, B., 2007.
Circulation and thermodynamics in a subglacial geothermal lake under the
Western Skaftá cauldron of the Vatnajökull ice cap, Iceland. Geophys. Res. Lett.
34 (19), L19502.
Kadish, S.J., Head, J.W., Parsons, R.L., Marchant, D.R., 2008. The Ascraeus Mons fanshaped deposit: Volcano–ice interactions and the climatic implications of coldbased tropical mountain glaciation. Icarus 197 (1), 84–109.
Kadish, S.J., Head III, J.W., Fastook, J.L., Marchant, D.R., 2014. Middle to Late
Amazonian tropical mountain glaciers on Mars: The ages of the Tharsis Montes
fan-shaped deposits. Planet. Space Sci. 91, 52–59.
Kminek, G., Bada, J.L., 2006. The effect of ionizing radiation on the preservation of
amino acids on Mars. Earth Planet. Sci. Lett. 245 (1–2), 1–5.
Lindén, M., Möller, P., Adrielsson, L., 2008. Ribbed moraine formed by subglacial
folding, thrust stacking and lee-side cavity infill. Boreas 37 (1), 102–131.
Lucchitta, B.K., 1981. Mars and Earth – Comparison of cold-climate features. Icarus
45 (2), 264–303.
Lucchitta, B.K., Anderson, D.M., Shoji, H., 1981. Did ice streams carve martian
outflow channels? Nature 290, 759–763.
Mader, H.M., Pettitt, M.E., Wadham, J.L., Wolff, E.W., Parkes, R.J., 2006. Subsurface
ice as a microbial habitat. Geology 34 (3), 169–172.
Malin, M.C. et al., 2007. Context camera investigation on board the Mars
Reconnaissance Orbiter. J. Geophys. Res.: Planets 112 (E5), E05S04.
Mangold, N., 2003. Geomorphic analysis of lobate debris aprons on Mars at Mars
Orbiter Camera scale: Evidence for ice sublimation initiated by fractures. J.
Geophys. Res.: Planets 108 (E4), 2-1–2-13.
Marchant, D.R., Head, J.W., Kreslavsky, M.A., 2006. Mid-latitude glacial modification
of Moreux Crater (44°E, 42°N; 135 km): Evidence for polythermal glaciation
related to impact-induced enhanced thermal gradients. In: Presented at Lunar
and Planetary Science Conference XXXVII, Abstract 1425.
Marteinsson, V.T. et al., 2013. Microbial communities in the subglacial waters of the
Vatnajokull ice cap, Iceland. ISME J. 7 (2), 427–437.
K.E. Scanlon et al. / Icarus 250 (2015) 18–31
Mikucki, J.A., Foreman, C.M., Sattler, B., Lyons, W.B., Priscu, J.C., 2004.
Geomicrobiology of Blood Falls: An iron-rich saline discharge at the terminus
of the Taylor Glacier, Antarctica. Aquat. Geochem. 10 (3–4), 199–220.
Mikucki, J.A. et al., 2009. A contemporary microbially maintained subglacial ferrous
‘‘ocean’’. Science 324 (5925), 397–400.
Milkovich, S.M., Head, J.W., Marchant, D.R., 2006. Debris-covered piedmont glacier
deposits along the northwest flank of the Olympus Mons scarp: Evidence for
low-latitude ice accumulation during the Late Amazonian of Mars. Icarus 181,
388–407.
Milliken, R.E., Mustard, J.F., Goldsby, D.L., 2003. Viscous flow features on the surface
of Mars: Observations from high-resolution Mars Orbiter Camera (MOC)
images. J. Geophys. Res.: Planets 108 (E6), 11-1–11-13.
Möller, P., 2006. Rogen moraine: An example of glacial reshaping of pre-existing
landforms. Quatern. Sci. Rev. 25 (3–4), 362–389.
Möller, P., 2010. Melt-out till and ribbed moraine formation, a case study from
south Sweden. Sed. Geol. 232 (3–4), 161–180.
Murray, A.E. et al., 2012. Microbial life at 13 °C in the brine of an ice-sealed
Antarctic lake. Proc. Natl. Acad. Sci. 109 (50), 20626–20631.
Neukum, G., Jaumann, R., 2004. HRSC: The high resolution stereo camera of Mars
Express. In: Wilson, A. (Ed.), Mars Express: The Scientific Payload. European
Space Agency, pp. 17–35.
Price, P.B., 2000. A habitat for psychrophiles in deep Antarctic ice. Proc. Natl. Acad.
Sci. 97 (3), 1247–1251.
Price, P.B., 2007. Microbial life in glacial ice and implications for a cold origin of life.
FEMS Microbiol. Ecol. 59 (2), 217–231.
Priscu, J.C. et al., 1999. Carbon transformations in a perennially ice-covered
Antarctic lake. Bioscience 49 (12), 997–1008.
Roberts, E.C., Laybourn-Parry, J., McKnight, D.M., Novarino, G., 2000. Stratification
and dynamics of microbial loop communities in Lake Fryxell, Antarctica.
Freshw. Biol. 44 (4), 649–661.
Scanlon, K.E., Head, J.W., Wilson, L., Marchant, D.R., 2014. Volcano–ice
interactions in the Arsia Mons tropical mountain glacier deposits. Icarus
237, 315–339.
Scott, D., Zimbelman, J., 1995. Geologic map of Arsia Mons Volcano, Mars. US
Geological Survey Miscellaneous Investigations Series, Map I-2480.
Scott, D.H., Dohm, J.M., Zimbelman, J.R., 1998. Geologic map of Pavonis Mons
Volcano, Mars. US Geological Survey Miscellaneous Investigations Series, Map I2561.
Shean, D.E., Head, J.W., Marchant, D.R., 2005. Origin and evolution of a cold-based
tropical mountain glacier on Mars: The Pavonis Mons fan-shaped deposit. J.
Geophys. Res.: Planets 110 (E5), E05001.
31
Shean, D.E., Head, J.W., Fastook, J.L., Marchant, D.R., 2007. Recent glaciation at high
elevations on Arsia Mons, Mars: Implications for the formation and evolution of
large tropical mountain glaciers. J. Geophys. Res.: Planets 112 (E3), E03004.
Shreve, R.L., 1985. Esker characteristics in terms of glacier physics, Katahdin esker
system, Maine. Geol. Soc. Am. Bull. 96 (5), 639–646.
Skidmore, M., 2011. Microbial communities in Antarctic subglacial aquatic
environments. Geophys. Monogr. Ser. 192, 61–81.
Smith, D.E. et al., 1999. The global topography of Mars and implications for surface
evolution. Science 284 (5419), 1495–1503.
Squyres, S.W., 1979. The distribution of lobate debris aprons and similar flows on
Mars. J. Geophys. Res.: Solid Earth 84 (B14), 8087–8096.
Squyres, S.W., Carr, M.H., 1986. Geomorphic evidence for the distribution of ground
ice on Mars. Science 231 (4735), 249–252.
Stibal, M. et al., 2012a. Methanogenic potential of Arctic and Antarctic subglacial
environments with contrasting organic carbon sources. Glob. Change Biol. 18
(11), 3332–3345.
Stibal, M., Šabacká, M., Žárský, J., 2012b. Biological processes on glacier and ice
sheet surfaces. Nat. Geosci. 5 (11), 771–774.
Stokes, C.R., Lian, O.B., Tulaczyk, S., Clark, C.D., 2008. Superimposition of ribbed
moraines on a palaeo-ice-stream bed: implications for ice stream dynamics and
shutdown. Earth Surf. Proc. Land. 33 (4), 593–609.
Summons, R.E. et al., 2011. Preservation of martian organic and environmental
records: Final report of the Mars biosignature working group. Astrobiology 11
(2), 157–181.
Thorseth, I., Torsvik, T., Torsvik, V., Daae, F., 2001. Diversity of life in ocean floor
basalt. Earth Planet. Sci. Lett. 194 (1), 31–37.
Wettlaufer, J.S., 1999. Impurity effects in the premelting of ice. Phys. Rev. Lett. 82
(12), 2516–2519.
Williams, R., 1978. Geomorphic processes in Iceland and on Mars: A comparative
appraisal from orbital images. Geol. Soc. Am. Abst. Prog. 10, 517.
Wilson, L., Head, J.W., 2007a. Arsia Mons cold-based tropical mountain glacier:
Subglacial eruptions, polythermal glaciation, and distal drainage of meltwater.
In: Presented at Volcano–Ice Interactions, vol. 2.
Wilson, L., Head, J.W., 2007b. Tropical mountain glaciers on Mars: Volcano–ice
interactions and influences on glacial evolution. In: Presented at 7th
International Conference on Mars.
Zimbelman, J.R., Edgett, K.S., 1992. The Tharsis–Montes, Mars – Comparison of
volcanic and modified landforms. In: Presented at Lunar and Planetary Science
Conference, XXII, pp. 31–44.
Zuber, M.T. et al., 1992. The Mars-observer laser altimeter investigation. J. Geophys.
Res.: Planets 97 (E5), 7781–7797.