Fresh shallow valleys in the Martian midlatitudes as features formed by meltwater flow beneath ice

Abstract

Significant numbers of valleys have been identified in the Martian midlatitudes (30-60°N/S), spatially associated with extant or recent ice accumulations. Many of these valleys date to the Amazonian, but their formation during these cold, dry epochs is problematic. In this study, we look in detail at the form, distribution, and quantitative geomorphology of two suites of these valleys and their associated landforms in order to better constrain the processes of their formation. Since the valleys themselves are so young and thus well preserved, uniquely, we can constrain valley widths and courses and link these to the topography from the Mars Orbiter Laser Altimeter and High-Resolution Stereo Camera data. We show that the valleys are both qualitatively and quantitatively very similar, despite their being >5000 km apart in different hemispheres and around 7 km apart in elevation. Buffered crater counting indicates that the ages of these networks are statistically identical, probably forming during the Late Amazonian,~100 Ma. In both localities, at least tens of valleys cross local drainage divides, apparently flowing uphill. We interpret these uphill reaches to be characteristic of flow occurring beneath a now absent, relatively thin (order 10 1 -10 2 m), regionally extensive ice cover. Ridges and mounds occasionally found at the foot of these valley systems are analogous to eskers and aufeis-like refreezing features. On the basis of their interaction with these aufeis-like mounds, we suggest that this suite of landforms may have formed in a single, short episode (perhaps order of days), probably forced by global climate change.

The Nature and Origin of Deposits in Uzboi Vallis on Mars

“…Evidence for an active hydrologic cycle in the Hesperian to Middle Amazonian is also supported by valleys in the midlatitudes of both hemispheres (e.g., Adeli et al, ; Dickson et al, ; Fassett & Head, , ; Hauber et al, ; Howard & Moore, ; Hynek et al, ; Salese et al, ; Warner et al, , ; Wilson et al, ). The catalyst for the climatic optimum that created warming is not known, but it could be related to variations in the insulation triggered by changes in obliquity (e.g., Laskar et al, ) or warming from ephemeral atmospheric changes (Hobley et al, ). Regardless, the growing geomorphic evidence for a post‐Noachian climate that was capable of supporting an active hydrologic cycle is intriguing, as surface conditions may have been habitable.…”

Glacier-like forms on Mars

“…present surface has also led to suggestions that continental glaciation may once have occurred on Mars (Kargel and Strom, 1992;Kargel et al, 1995;Fastook et al, 2014;Hobley et al, 2014).…”

Mars: a small terrestrial planet

“…In contrast, new high-resolution images display small, narrow valleys (<100 km long) that represent local fluvial activity scattered in various locations of Mars, but especially in the mid-latitudes. Some of these valleys occur in association with glacial landforms as supra-glacial flows (Fassett et al 2010) or sub-glacial melting (Hobley et al 2014). Many valleys are observed in the mid-latitudes (30 • -45 • ) where ice is known to be present as a latitude-dependent mantle (Mangold 2012).…”

“…While these valleys are clearly influenced by the presence of ground or surface-ice, the mechanism of melting is debated. Examples on the ejecta of craters point toward heating by impact warming (Jones et al 2011), but episodic climate change has been invoked as well (Hobley et al 2014). These observations may be connected to small valleys observed on volcanoes and may be related to volcanic/geothermal heating, especially on Alba Patera (Gulick and Baker 1990) which have Early Amazonian age and were a unique example of Amazonian valleys at the time of their discovery.…”