MARTIAN EROSION RATES DURING AMAZONIAN GLACIATION SUGGEST COLD-BASED FLOW AND ARID CLIMATE DENUDATION RATES

Observations of Mars from the surface and from orbit suggest that erosion rates over the last ~3 Gyr (the Amazonian) have been as slow as 10^-5 m/Myr and have been dominated by aeolian processes, while ancient (Noachian) erosion rates may have been orders of magnitude higher due to impact bombardment and fluvial activity. Amazonian-aged glacial deposits are widespread on Mars, but rates of erosion responsible for contributing debris to these remnant glacial deposits have not been constrained. Here, we calculate erosion rates during Amazonian glaciations using a catalog of mid-latitude glacial landforms coupled with observational and theoretical constraints on the duration of glaciation. Supraglacial debris thickness was estimated to be ~10 m based on SHARAD observations of maximum debris thickness in addition to geomorphic indicators of debris thickness from impact craters. Debris area was constrained by totaling the surface area of ~11,000 mapped lobate debris aprons (LDA), lineated valley fill deposits (LVF), and concentric crater fill deposits (CCF). Together, these areas and thicknesses produced an estimate of supraglacial debris volume (not including englacial debris or dust). The area of scarps, massifs, and valley walls eroded to generate this debris volume was determined by interrogating the MOLA 128 ppd gridded topography dataset to identify pixels within 5 km of LVF, LDA, and CCF that had slopes exceeding 5˚ and that were within the rockshed of the remnant glacial landforms (i.e., not located outside the crater or across a drainage divide). Dividing eroded volume by denuded area produces a linear measure of eroded thickness. Dividing this average eroded thickness by the minimum and maximum rates of glacier emplacement on Mars (~600 Myr for all glacial deposits, versus ~500 kyr for the emplacement of a single LDA) yields a bracketed range of erosion rates needed to generate the debris in martian relict glacial features. These calculations suggest that erosion rates for scarps that contributed debris to glacial landforms are 4-7 orders of magnitude higher than average Amazonian rates in non-glaciated, low-slope regions. These erosion rates are similar to terrestrial cold-based glacier erosion and entrainment rates, strongly suggesting cold-based glacier modification of parts of Mars.