Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars

Abstract

This paper investigates the influences of palaeohydrology and geologicaltopographic inheritance in shaping the channel of the lower River Suir, southeast Ireland. Results of acoustic surveys of the lower River Suir and Waterford Harbour reveal two scales of pseudo-cyclic river bedforms. Longitudinal elevation profiles of the geological topography (undulating bedrock and till-mantled bedrock) bounding the present floodplain swath reveal pseudo-cyclicity in that terrain too. Spectral and statistical analyses are used to quantify the cyclicity of the long profile and geological-topographic series. These methods show that the dominant cyclicity of the long profile reflects autocorrelation more than inheritance of cyclicity from the bounding geological topography. The cyclicity of the long profile mainly reflects a hydraulic control on pool-spacing, although some cyclicity probably has been inherited from the geological-topography. Channel-forming palaeodischarge is estimated based on the dominant pool-spacing revealed by spectral analysis, validated using relationships between meander wavelength, channel cross-sectional geometry and hydraulically-informed discharge reconstruction. The palaeodischarge estimates are in close agreement and are two orders of magnitude greater than present flood maxima. Significantly, these palaeodischarge estimates also agree closely with palaeodischarge calculated for the submerged Pleistocene palaeochannel that extends across the near-shore continental shelf from Waterford Harbour. The pool-sequence of the lower Suir and the submerged palaeochannel represent a former land-system that was active during a period of low relative sea level during the last glacial. More broadly, the paper offers insights into the landscape evolution of formerly glaciated regions that experienced very wide This article is protected by copyright. All rights reserved. discharge variability during and after the transition from glacial to interglacial regimes, in a context of complex relative sea level change.

Recent Basal Melting of a Mid‐Latitude Glacier on Mars

“…The lack of morphological evidence for prolonged supraglacial or subglacial melting (e.g., supraglacial channels, fans, and streamlined bedforms) leads us to exclude such a regional climate anomaly as the sole driver of wet‐based glaciation in the Tempe Terra rift. Thus, while we do not exclude climate warming as a possible contributing factor in inducing wet‐based glaciation, we argue that perturbation of basal ice temperatures by a geothermal heat flux anomaly (Gallagher & Balme, ) is more consistent with the tectonic setting and our geomorphic observations.…”

“…The lack of morphological evidence for prolonged supraglacial or subglacial melting (e.g., supraglacial channels, fans, and streamlined bedforms) leads us to exclude such a regional climate anomaly as the sole driver of wet-based glaciation in the Tempe Journal of Geophysical Research: Planets 10.1002/2017JE005434 Terra rift. Thus, while we do not exclude climate warming as a possible contributing factor in inducing wetbased glaciation, we argue that perturbation of basal ice temperatures by a geothermal heat flux anomaly (Gallagher & Balme, 2015) is more consistent with the tectonic setting and our geomorphic observations. While primary geothermal anomalies associated with the formation of the ancient rift in Tempe Terra (Hauber et al, 2010) are unlikely to have persisted into the Amazonian, magmato-tectonic processes could have exploited preexisting structural weaknesses in their vicinity to induce geothermal anomalies coincident with recent glaciation.…”

“…To our knowledge, one other example of an esker associated with a late Amazonian‐aged (~150 Ma) mid‐latitude VFF has been documented to date, in a graben in Phlegra Montes, NE of the Elysium volcanic province (Gallagher & Balme, ). These young, mid‐latitude, VFF‐linked candidate eskers are distinct from other candidate eskers on Mars (see section 4.5) in their age, mid‐latitude location, and association with an extant parent glacier.…”

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.…”

Grid Mapping the Northern Plains of Mars: A New Overview of Recent Water‐ and Ice‐Related Landforms in Acidalia Planitia

“…Sublimation of glacial ice (e.g., as dry ablation hollows; Mangold, ) would indeed leave a rimmed depression, but only if some material had accumulated along the ice margins, for example, as ice‐sediment contact or drop moraines at the margins of cold‐based glaciers (Atkins, ). If there was ever any glacial ice, it would probably have been cold based as no proglacial or glaciofluvial features such as channels or eskers (Fassett et al, ; Gallagher & Balme, ) were observed. A repeated sequence of past ice accumulation and sublimation could explain the nested occurrence of pits (Figure a).…”