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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.02.021 Byline: Caleb I. Fassett (a), James L. Dickson (a), James W. Head (a), Joseph S. Levy (b), David R. Marchant (c) Keywords: Mars; Mars, surface; Mars, climate; Geological processes Abstract: Abundant evidence exists for glaciation being an important geomorphic process in the mid-latitude regions of both hemispheres of Mars, as well as in specific environments at near-equatorial latitudes, such as along the western flanks of the major Tharsis volcanoes. Detailed analyses of glacial landforms (lobate-debris aprons, lineated valley fill, concentric crater fill, viscous flow features) have suggested that this glaciation was predominantly cold-based. This is consistent with the view that the Amazonian has been continuously cold and dry, similar to conditions today. We present new data based on a survey of images from the Context Camera (CTX) on the Mars Reconnaissance Orbiter that some of these glaciers experienced limited surface melting, leading to the formation of small glaciofluvial valleys. Some of these valleys show evidence for proglacial erosion (eroding the region immediately in front of or adjacent to a glacier), while others are supraglacial (eroding a glacier's surface). These valleys formed during the Amazonian, consistent with the inferred timing of glacial features based on both crater counts and stratigraphic constraints. The small scale of the features interpreted to be of glaciofluvial origin hindered earlier recognition, although their scale is similar to glaciofluvial counterparts on Earth. These valleys appear qualitatively different from valley networks formed in the Noachian, which can be much longer and often formed integrated networks and large lakes. The valleys we describe here are also morphologically distinct from gullies, which are very recent fluvial landforms formed during the last several million years and on much steeper slopes ([approximately equal to]20-30[degrees] for gullies versus a*10[degrees] for the valleys we describe). These small valleys represent a distinct class of fluvial features on the surface of Mars (glaciofluvial); their presence shows that the hydrology of Amazonian Mars is more diverse than previously thought. Author Affiliation: (a) Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, RI 02912, USA (b) Department of Geology, Portland State University, 1721 SW Broadway, Portland, OR 97201, USA (c) Department of Earth Sciences, Boston University, Boston, MA 02215, USA Article History: Received 21 September 2009; Revised 24 February 2010; Accepted 28 February 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.03.019 Byline: Seth J. Kadish (a), James W. Head (a), Rebecca L. Parsons (b), David R. Marchant (c) Keywords: Ices; Volcanism; Mars; climate; Geological processes Abstract: Amazonian-aged fan-shaped deposits extending to the northwest of each of the Tharsis Montes in the Tharsis region on Mars have been interpreted to have originated from mass-wasting, volcanic, tectonic and/or glacial processes. We use new data from MRO, MGS, and Odyssey to characterize these deposits. Building on recent evidence for cold-based glacial activity at Pavonis Mons and Arsia Mons, we interpret the smaller Ascraeus fan-shaped deposit to be of glacial origin. Our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat, including: (1) a ridged facies, interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat, (2) a knobby facies, interpreted to represent vertical downwasting of the ice sheet, and (3) complex ridges showing a cusp-like structure. We also see evidence of volcano-ice interactions in the form of: (1) an arcuate inward-facing scarp, interpreted to have formed by the chilling of lava flows against the glacial margin, (2) a plateau feature, interpreted to represent a subglacial eruption, and (3) knobby facies superimposed on flat-topped flows with leveed channels, interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till. We discuss the formation mechanisms of these morphologies during cold-based glacial activity and concurrent volcanism. On the basis of a Mid- to Late-Amazonian age (250-380 Ma) established from crater size-frequency distribution data, we explore the climatic implications of recent glaciation at low latitudes on Mars. GCM results show that increased insolation to the poles at high obliquities (>45[degrees]) forces sublimation of polar ice, which is transported to lower latitudes and deposited on the flanks of the Tharsis Montes. We assess how local orographic effects, the mass balance of the glacier, and the position of equilibrium line altitudes, all played a role in producing the observed geomorphologies. In doing so, we outline a glacial history for the evolution of the Ascraeus Mons fan-shaped deposit and compare its initiation, growth and demise with those of Arsia Mons and Pavonis Mons. Author Affiliation: (a) Department of Geological Sciences, Brown University, Providence, RI 02912, USA (b) Department of Geosciences, Stony Brook University, New York, NY 11794, USA (c) Department of Earth Sciences, Boston University, Boston, MA 02215, USA Article History: Received 24 October 2007; Revised 13 February 2008

Abstract: We modeled water–vapor diffusion within Mullins till, a relatively dry supraglacial till in southern Victoria Land, Antarctica, that rests directly on Mullins Glacier, purportedly one of the oldest alpine glaciers in the world. Like most supraglacial tills in cold-desert environments, Mullins till contains three characteristic facies: a weathered facies representing the oxidation of iron-bearing minerals and the physical disintegration of surface rocks; a sand-wedge facies representing the episodic infill of thermal cracks associated with contraction-crack polygons; and an underlying fresh facies representing the addition of englacial debris (sourced from rockfall) as overlying ice sublimes. Using a one-dimensional model for Fickian vapor diffusion through porous media, we show that the rate of subsurface ice sublimation varies by ~5.5% beneath till facies and that over timescales of 105 years diffusion through “porous” sand wedges contributes to the development of deep troughs surrounding high-centered polygons. Applying site-specific meteorological data collected over a four-year period, we show that ice loss at the stagnant terminus of Mullins Glacier is ~6.6×10−5 m a−1, a value that (although low and assuming an ice thickness of ~150m) is consistent with complete ice loss under current environmental forcing in ~2.5Ma. Our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months. Calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of ~6.4°C or an increase in atmospheric relative humidity from 44% to 75%, both of which could arise from an increase in cloud cover over Mullins Glacier. Sublimation responses to meteorological forcing are not uniform across Mullins Glacier. A summer increase in soil temperature of 2°C results in negligible change in ice sublimation at Mullins terminus, but a 27% increase in ice loss in upper Mullins Valley. The key factor is the thickness of Mullins till, which is greater near the glacier terminus. For till thicknesses exceeding ~25cm, non-linear variations in soil temperature result in downward vapor fluxes, capable of producing thin, cm-scale lenses of secondary pore that cap the surface of buried glacier ice. This downward vapor flow, sourced from modern snowfall and/or elevated atmospheric relative humidity, is one of the key factors that enable long-term preservation of buried glacier ice. Overall, our results highlight the subtle relations among changes in till texture, till thickness, and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi-million-year-old ice can exist beneath thin supraglacial tills, <~50-cm thick, in southern Victoria Land, Antarctica. [Copyright &y& Elsevier]

Abstract: Lobate debris aprons (LDA) and lineated valley fill (LVF) have been known to characterize the mid-latitude regions of Mars since documented by Viking; their flow-like character suggested that deposition of ice in talus pile pore space caused lubrication and flow during an earlier climatic regime. A number of factors have remained uncertain, however, including the detailed structure and texture of LDA/LVF, the relationships between them, their direction of flow, the origin and abundance of the lubricating agent, and their exact mode of origin (e.g., ice-assisted rock creep, ice-rich landslides, rock glaciers, debris-covered glaciers). We use new High-Resolution Stereo Camera (HRSC) image and topography data, in conjunction with a range of other post-Viking data sets, and new insights provided by cold-based terrestrial glacial analogs, to assess the characteristics of LDA/LVF in the northern mid-latitudes of Mars. We find evidence that the characteristics and flow patterns of the LDA and LVF are most consistent with Late Amazonian debris-covered glacial valley landsystems. The broad distribution and integrated characteristics of the LDA/LVF systems suggest that earlier in the Amazonian, climatic conditions were such that significant snow and ice accumulated on mid-latitude plateaus and in valleys, producing integrated glacial landsystems, the remnants of which are preserved today beneath residual sublimation till derived from adjacent valley walls. Atmospheric general circulation models suggest that these climatic conditions occurred when Mars was at a spin-axis obliquity of ~35°, and the atmosphere was relatively dusty. Glacial flow modeling under these conditions produces patterns similar to those documented in the LDA/LVF, and SHARAD radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today. [Copyright &y& Elsevier]

The article discusses the study which examines the ground-penetrating radar (GPR) and seismic surveys for the Mullins Valley debris-covered glacier called Mullins Glacier in Antarctica. It indicates that the glacier yields a local ice-thickness estimates of 80110m in upper Mullins Valley and 150m in upper Beacon Valley. It notes that the englacial debris layer appears as a coherent reflector dipping 40458 up-valley and intersects the ground surface with the largest of several ridges that mark the glacier surface. The field excavations reveal that the englacial interface consists of multiple debris bands that can be directly correlated with ridge microtopography.

We map polygonally patterned ground formed in sublimation tills that overlie debris-covered glaciers in Mullins Valley and central Beacon Valley, in southern Victoria Land, Antarctica, and distinguish five morphological zones. Where the Mullins Valley debris-covered glacier debouches into Beacon Valley, polygonal patterning transitions from radial (orthogonal) intersections to non-oriented (hexagonal) intersections, providing a time-series of polygon evolution within a single microclimate. We offer the following model for polygon formation and evolution in the Mullins Valley system. Near-vertical cracks that ultimately outline polygons are produced by thermal contraction in the glacier ice. Some of these cracks may initially be oriented radial to maximum surface velocities by pre-existing structural stresses and material weaknesses in the glacier ice. In areas of relatively rapid flow, polygons are oriented down-valley forming an overall fan pattern radial to maximum ice velocity. As glacier flow moves the cracks down-valley, minor variations in flow rate deform polygons, giving rise to deformed radial polygons. Non-oriented (largely hexagonal) polygons commonly form in regions of stagnant and/or near-stagnant ice. We propose that orientation and morphology of contraction-crack polygons in sublimation tills can thus be used as an indicator of rates of subsurface ice flow. [ABSTRACT FROM AUTHOR]

Surface environmental conditions on Mars are currently extremely cold and hyperarid, most equivalent to polar deserts on Earth. Coupling newly acquired Mars data with field-based observations regarding the flow, surface morphology, and depositional history of polar glaciers in Antarctica, we show that the multiple facies of an extensive fan-shaped deposit on the western flanks of Arsia Mons volcano are consistent with deposition from cold-based mountain glaciers. An outer ridged facies that consists of multiple laterally extensive, arcuate and parallel ridges, resting without disturbance on both well-preserved lava flows and an impact crater, is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold-based glacier. A knobby facies that consists of equidimensional knobs, each to several kilometers in diameter, is inward of the ridges; this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice. A third facies comprising distinctive convex-outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock-glacier deposits, some of which may still be underlain by a core of glacier ice. Taken together, these surficial deposits show that the western flank of Arsia Mons was occupied by an extensive mountain glacial system accumulating on, and emerging from, the upper slopes of the volcano and spreading downslope to form a piedmont-like fan. [ABSTRACT FROM AUTHOR]

Reports on the discovery of buried glacier ice in Beacon Valley, East Antarctica that had survived for at least 8.1 million years. Preservation of Miocene glacier ice; Survival of vegetation on coastal mountains; Isotope and crystal fabric analyses of the ice show derived from an ice sheet; Persistence of polar conditions in region to avoid sublimation of ice.

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. [ABSTRACT FROM AUTHOR]

Abstract: Currently, and throughout much of the Amazonian, the mean annual surface temperatures of Mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold-based. The documented evidence for extensive and well-developed eskers (sediment-filled former sub-glacial meltwater channels) in the south circumpolar Dorsa Argentea Formation is an indication that basal melting and wet-based glaciation occurred at the South Pole near the Noachian–Hesperian boundary. We employ glacial accumulation and ice-flow models to distinguish between basal melting from bottom-up heat sources (elevated geothermal fluxes) and top-down induced basal melting (elevated atmospheric temperatures warming the ice). We show that under mean annual south polar atmospheric temperatures (−100°C) simulated in typical Amazonian climate experiments and typical Noachian–Hesperian geothermal heat fluxes (45–65mW/m2), south polar ice accumulations remain cold-based. In order to produce significant basal melting with these typical geothermal heat fluxes, the mean annual south polar atmospheric temperatures must be raised from today’s temperature at the surface (−100°C) to the range of −50 to −75°C. This mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water, and thus does not favor a “warm and wet” early Mars. Seasonal temperatures at lower latitudes, however, could range above the melting point of water, perhaps explaining the concurrent development of valley networks and open basin lakes in these areas. This treatment provides an independent estimate of the polar (and non-polar) surface temperatures near the Noachian–Hesperian boundary of Mars history and implies a cold and relatively dry Mars climate, similar to the Antarctic Dry Valleys, where seasonal melting forms transient streams and permanent ice-covered lakes in an otherwise hyperarid, hypothermal climate. [Copyright &y& Elsevier]

Abstract: Hypotheses accounting for the formation of concentric crater fill (CCF) on Mars range from ice-free processes (e.g., aeolian fill), to ice-assisted talus creep, to debris-covered glaciers. Based on analysis of new CTX and HiRISE data, we find that concentric crater fill (CCF) is a significant component of Amazonian-aged glacial landsystems on Mars. We present mapping results documenting the nature and extent of CCF along the martian dichotomy boundary over −30 to 90°E latitude and 20–80°N longitude. On the basis of morphological analysis we classify CCF landforms into “classic” CCF and “low-definition” CCF. Classic CCF is most typical in the middle latitudes of the analysis area (∼30–50°N), while a range of degradation processes results in the presence of low-definition CCF landforms at higher and lower latitudes. We evaluate formation mechanisms for CCF on the basis of morphological and topographic analyses, and interpret the landforms to be relict debris-covered glaciers, rather than ice-mobilized talus or aeolian units. We examine filled crater depth–diameter ratios and conclude that in many locations, hundreds of meters of ice may still be present under desiccated surficial debris. This conclusion is consistent with the abundance of “ring-mold craters” on CCF surfaces that suggest the presence of near-surface ice. Analysis of breached craters and distal glacial deposits suggests that in some locations, CCF-related ice was once several hundred meters higher than its current level, and has sublimated significantly during the most recent Amazonian. Crater counts on ejecta blankets of filled and unfilled craters suggests that CCF formed most recently between ∼60 and 300Ma, consistent with the formation ages of other martian debris-covered glacial landforms such as lineated valley fill (LVF) and lobate debris aprons (LDA). Morphological analysis of CCF in the vicinity of LVF and LDA suggests that CCF is a part of an integrated LVF/LDA/CCF glacial landsystem. Instances of morphological continuity between CCF, LVF, and LDA are abundant. The presence of formerly more abundant CCF ice, coupled with the integration of CCF into LVF and LDA, suggests the possibility that CCF represents one component of the significant Amazonian mid-latitude glaciation(s) on Mars. [Copyright &y& Elsevier]

Abstract: A variety of Late Amazonian landforms on Mars have been attributed to the dynamics of ice-related processes. Evidence for large-scale, mid-latitude glacial episodes existing within the last 100 million to 1 billion years on Mars has been presented from analyses of lobate debris aprons (LDA) and lineated valley fill (LVF) in the northern and southern mid-latitudes. We test the glacial hypothesis for LDA and LVF along the dichotomy boundary in the northern mid-latitudes by examining the morphological characteristics of LDA and LVF surrounding two large plateaus, proximal massifs, and the dichotomy boundary escarpment north of Ismeniae Fossae (centered at 45.3°N and 39.2°E). Lineations and flow directions within LDA and LVF were mapped using images from the Context (CTX) camera, the Thermal Emission Imaging Spectrometer (THEMIS), and the High Resolution Stereo Camera (HRSC). Flow directions were then compared to topographic contours derived from the Mars Orbiter Laser Altimeter (MOLA) to determine the down-gradient components of LDA and LVF flow. Observations indicate that flow patterns emerge from numerous alcoves within the plateau walls, are integrated over distances of up to tens of kilometers, and have down-gradient flow directions. Smaller lobes confined within alcoves and superposed on the main LDA and LVF represent a later, less extensive glacial phase. Crater size-frequency distributions of LDA and LVF suggest a minimum (youngest) age of 100Ma. The presence of ring-mold crater morphologies is suggestive that LDA and LVF are formed of near-surface ice-rich bodies. From these observations, we interpret LDA and LVF within our study region to result from formerly active debris-covered glacial flow, consistent with similar observations in the northern mid-latitudes of Mars. Glacial flow was likely initiated from the accumulation and compaction of snow and ice on plateaus and in alcoves within the plateau walls as volatiles were mobilized to the mid-latitudes during higher obliquity excursions. Together with similar analyses elsewhere along the dichotomy boundary, these observations suggest that multiple glacial episodes occurred in the Late Amazonian and that LDA and LVF represent significant reservoirs of non-polar ice sequestered below a surface lag for hundreds of millions of years. [Copyright &y& Elsevier]

Abstract: Fan-shaped deposits up to in area are found on the northwest flanks of the huge Tharsis Montes volcanoes in the tropics of Mars. Recent spacecraft data have confirmed earlier hypotheses that these lobate deposits are glacial in origin. Increased knowledge of polar-latitude terrestrial glacial analogs in the Antarctic Dry Valleys has been used to show that the lobate deposits are the remnants of cold-based glaciers that formed in the extremely cold, hyper-arid climate of Mars. Mars atmospheric general circulation models (GCM) show that these glaciers could form during periods of high obliquity when upwelling and adiabatic cooling of moist air favor deposition of snow on the northwest flanks of the Tharsis Montes. We present a simulation of the Tharsis Montes ice sheets produced by a static accumulation pattern based on the GCM results and compare this with the nature and extent of the geologic deposits. We use the fundamental differences between the atmospheric snow accumulation environments (mass balance) on Earth and Mars, geological observations and ice-sheet models to show that two equilibrium lines should characterize ice-sheet mass balance on Mars, and that glacial accumulation should be favored on the flanks of large volcanoes, not on their summits as seen on Earth. Predicted accumulation rates from such a parameterization, together with sample spin-axis obliquity histories, are used to show that obliquity in excess of 45° and multiple 120,000 year obliquity cycles are necessary to produce the observed deposits. Our results indicate that the formation of these deposits required multiple successive stages of advance and retreat before their full extent could be reached, and thus imply that spin-axis obliquity remained at these high values for millions of years during the Late Amazonian period of Mars history. Spin-axis obliquity is one of the main factors in the distribution and intensity of solar insolation, and thus in determining the climate history of Mars. Unfortunately, reconstruction of past climate history is inhibited by the fact that the chaotic nature of the solution makes the calculation of orbital histories unreliable prior to about 20 Ma ago. We show, however, that the geological record, combined with glacial modeling, can be used to provide insight into the nature of the spin-axis/orbital history of Mars in the Late Amazonian, and to begin to establish data points for the geologically based reconstruction of the climate and orbital history of Mars. [Copyright &y& Elsevier]

Lineated valley fi ll (LVF) in fretted valleys at the dichotomy boundary has been interpreted as glacial in origin. Unknown are (1) the original thickness of the glacier ice, (2) the amount of ice-surface lowering, through sublimation and retreat, to its presently observed level, and (3) whether there were multiple periods of glaciation. We address these questions through analysis of an LVF glacial system. The elevation difference between the upper limit of a previous highstand and the current surface of the LVF at the study site is 920 m. We interpret this difference to be the minimum amount of ice-surface lowering of the glacier system. Consistent with a general lowering of the ice surface are multiple moraines and/or trimlines, and changes in LVF flow patterns, as the ice retreated and decreased in thickness. The superposition of several lobes onto the current surface of the LVF indicates that a phase of alpine glaciation followed the lowering of the valley glacial system. These data suggest that the Late Amazonian glaciation that produced LVF in this region involved significantly larger amounts of ice than previously thought, and that subsequent alpine glaciation followed. [ABSTRACT FROM AUTHOR]

Highlights: [•] We survey glaciovolcanic landforms in the glacial deposit on the Arsia Mons volcano. [•] We find evidence for pillow and hyaloclastite mounds, ice-confined flows, and a tuya. [•] Construction of these edifices would have melted hundreds of cubic kilometers of ice. [•] The glaciovolcanic meltwater bodies may have persisted on 100–1000year timescales. [Copyright &y& Elsevier]