Recent Basal Melting of a Mid‐Latitude Glacier on Mars

Abstract

Evidence for past basal melting of young (late Amazonian‐aged), debris‐covered glaciers in Mars' mid‐latitudes is extremely rare. Thus, it is widely thought that these viscous flow features (VFFs) have been perennially frozen to their beds. We identify an instance of recent, localized wet‐based mid‐latitude glaciation, evidenced by a candidate esker emerging from a VFF in a tectonic rift in Tempe Terra. Eskers are sedimentary ridges deposited in ice‐walled meltwater conduits and are indicative of glacial melting. We compare the candidate esker to terrestrial analogues, present a geomorphic map of landforms in the rift, and develop a landsystem model to explain their formation. We propose that the candidate esker formed during a transient phase of wet‐based glaciation. We then consider the similarity between the geologic setting of the new candidate esker and that of the only other candidate esker to be identified in association with an existing mid‐latitude VFF; both are within tectonic graben/rifts proximal to volcanic provinces. Finally, we calculate potential basal temperatures for a range of VFF thicknesses, driving stresses, mean annual surface temperatures, and geothermal heat fluxes, which unlike previous studies, include the possible role of internal strain heating. Strain heating can form an important additional heat source, especially in flow convergence zones, or where ice is warmer due to elevated surface temperatures or geothermal heat flux. Elevated geothermal heat flux within rifts, perhaps combined with locally‐elevated strain heating, may have permitted wet‐based glaciation during the late Amazonian, when cold climates precluded more extensive wet‐based glaciation on Mars.

Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today

“…On Earth, high geothermal heat fluxes of >200 mW/m 2 have been observed beneath the Antarctic ice sheet (Fisher et al, 2015;Schroeder et al, 2014), much greater than the average terrestrial value. Models of Martian midlatitude glaciation similarly found that increases in geothermal heat flux were needed to achieve subglacial melting but also required strain heating of the ice due to internal deformation of flowing ice (Butcher et al, 2017). However, most of these factors are either already accounted for in the models that predict Mars' low geothermal heat flux (such as crustal thickness) or are not applicable to Mars (such as factors related to plate tectonics).…”

“…However, most of these factors are either already accounted for in the models that predict Mars' low geothermal heat flux (such as crustal thickness) or are not applicable to Mars (such as factors related to plate tectonics). Models of Martian midlatitude glaciation similarly found that increases in geothermal heat flux were needed to achieve subglacial melting but also required strain heating of the ice due to internal deformation of flowing ice (Butcher et al, 2017). This effect is not observed to be occurring in the polar layered deposits (Karlsson et al, 2011), nor is it predicted to occur except possibly at some margins (Sori et al, 2016).…”

Glacial and gully erosion on Mars: A terrestrial perspective

“…The VFFs are believed to behave like cold-based glaciers on Earth, where the ice is frozen to the bed and the flow is dominated by deformation of mass above by gravity-driven viscous creep (Mangold and Allemand, 2001;Pierce and Crown, 2003;Li et al, 2005;Karlsson et al, 2015). Only in two locations have eskers been linked to VFF, providing evidence of basal glacial melting (Gallagher and Balme, 2015;Butcher et al, 2017). Rare supraglacial valleys have been attributed to transient supraglacial melting encouraged by focussing of solar radiation onto VFF surfaces from steep adjacent topography (Fassett et al, 2010).…”

Episodic and Declining Fluvial Processes in Southwest Melas Chasma, Valles Marineris, Mars

“…The planform geometry of these ridges is strong evidence that they are depositional channel systems now preserved as inverted relief (inverted fluvial channels; Burr et al, ; Davis et al, ; Pain et al, ; Williams et al, ). These ridges are interpreted as inverted fluvial channels rather than glacial eskers as they conform to regional topography (i.e., they do not go upslope) and lack associated glacier landforms commonly found with eskers (e.g., Butcher et al, ; Gallagher & Balme, ). Alternatively, the ridges may be the eroded remnants of erosional valley walls; however, given that multiple tributary ridges converge in the downslope direction, they are more consistent with inverted channels.…”