Can Venusian Channels Form by Subsurface Thermal Erosion?

Introduction: Channel formation is a unique puzzle in Venus' rock record. Channels, open passages believed to have transported fluid [1], occur in presumed volcanic regions [2], which together with current Venus surface conditions (~450º C [3] and ~100 bars surface pressure [4]), has led many workers, including us, to infer a volcanic origin for venusian channels, although an origin involving liquid water cannot be fully excluded [1, 5; see also, 6-7]. Any hypothesis regarding the formation of venusian channels must explain channel characteristics that include the apparent incision of a substrate with mostly consistent widths of 1-3 km for distances of up to 1000s of km [1], large apparent width to depth ratios, the general absence of levees [8] and extensive lateral flow deposits, and the lack of tributaries and cutoff meanders. Although it is likely that venusian channels form by more than one process, the processes remain largely speculative. Proposed mechanisms of venusian channel formation range from constructional processes [9] to mechanical [5, 10-11] and/or thermal erosion [8]. Fluids proposed to carve the channels range from water to basalt to komatiite to carbonatite. The proposed processes and fluids vary based on assumptions regarding the interface and/or substrate in which channels form [e.g., 1-2, 5, 8-12]. The purpose of this contribution is to continue investigating processes of venusian channel formation. We focus our work by presenting our first steps in numerically modeling venusian channels forming through thermal erosion in the subsurface. We explore the possibility and implications that some venusian channels form by lava flowing along a subsurface boundary where lava thermally erodes overlying materials. Background: This study builds on the work of [12] who analyzed three widely separate study areas on Venus with the explicit goal of delineating the geo-logic history of specific venusian channels. Based largely on the observation that channels in the three study areas dissect pre-existing topographic highs (wrinkle ridges and small shield edifices) with no deflection in the channel course, [12] argues that at least some channels on Venus are carved from below in a process similar to piping [13] instead of at the surface as assumed in earlier hypotheses. Termed the stoping hypothesis [12], venusian channels may form by fluid (likely lava) that flows along a shallow subsurface interface between two geologic units. The flowing