Alexander Dumke

Fill and spill of giant lakes in the eastern Valles Marineris region of Mars

The existence of Hesperian age (3.7–3.4 Ga) surface water bodies on Mars is a contentious issue, often conflicting with favored climate models. Extensive lakes are proposed to have filled parts of Valles Marineris during this period, yet evidence for their presence and temporal continuity is poorly constrained. Here we report geomorphic and chronologic evidence for the initiation and demise of a voluminous lake system within the basins of eastern Valles Marineris. We find that independent, kilometer-deep lakes were present here well after the wetter, global climate optimum that characterized the previous Noachian epoch (4.1–3.7 Ga). Relative and impact crater chronologies of flood channels emerging from lake basins indicate relatively late lake spillover in the Early Amazonian (ca. 3.0 Ga). Drawdown of the lake and cessation of interbasin sedimentation may be recorded by a similar Early Amazonian (ca. 3.1 Ga) crater retention age on the surface of Capri Mensa, a 4-km-tall, sulfate-bearing interior layered deposit. The topography data demonstrate that incision of the bedrock barriers between the basins during spillover was driven by a dramatic local base-level difference between the lake surface and downstream basin floors. We postulate that the lake spillover process created an integrated drainage routing system between a voluminous equatorial water supply and the northern plains basin.

Periglacial geomorphology and landscape evolution of the Tempe Terra region, Mars

Abstract A systematic survey was undertaken and an investigation carried out into the geomorphological characteristics of lobate debris aprons in the Tempe Terra region of Mars. Based on the most recent high-resolution (sub 15 m per pixel) imagery and on new topography data, this study endeavoured to raise and discuss questions regarding their formation (emplacement) and modification (deformation sequence), as well as the role of a mantling deposit found at mid-latitude locations on Mars. Furthermore, a model for the formation of debris aprons in the Tempe Terra–Mareotis Fossae settings is proposed. Image survey, in combination with basic morphometric observations within a geomorphological context, provided additional insights into the source, emplacement and modification of hillslope debris material. Our results imply that lobate debris aprons are not mainly relicts of remnant degradation but are substantially composed of mantling material probably deposited episodically in the course of planetary obliquity changes and over a long timespan, as derived erosion rates suggest. Crater-size frequency statistics and the derivation of absolute ages show ages of sub-recent modification and document earlier resurfacing events.

Evolution of periglacial landforms in the ancient mountain range of the Thaumasia Highlands, Mars

Abstract Possible periglacial and relict glacial landforms in the ancient mountain range of the Thaumasia Highlands, Mars, are described. The landforms include large-scale mantling, lineated crater and valley-fill materials, debris aprons, protalus lobes and ramparts. The most pristine ice-related landforms appear to be small-scale protalus lobes and ramparts with no visible distinct impact craters at both medium (High Resolution Stereo Camera (HRSC)) and high (Mars Orbiter Camera (MOC) narrow angle (NA), Context Camera (CTX)) spatial resolution. These small landforms are possibly active at present and post-date more extensive features such as crater fills, possibly formed during high obliquity climatic periods. In contrast to the rock glacier-like landforms with distribution preferentially occurring on south-facing slopes, possibly controlled by enhanced exposure to the Sun, older, less pristine lineated fill materials show a less systematic distribution of flow directions, suggesting a more generalized periglacial and possibly glacial environment in the Thaumasia Highlands.