GROUND-BASED THERMAL IMAGING OF AN INACTIVE ROCK GLACIER AS ANALOG TO MARTIAN DEBRIS APRONS

Lobate debris aprons on Mars are considered analogous to terrestrial rock glaciers due to similarities in geormorphology: both are typically steep-margined, spatulate features sourced from topographic highs such as massif walls or cirques. Previous studies of Martian debris aprons have identified variations in thermophysical properties (as evidenced by variations in nighttime temperature observed in thermal infrared images) that may be related to the mode of formation. Of particular interest is the possibility that these variations may be related to the relationship of rock and ice in the interior of the feature: debris-covered glaciers (massive ice covered by a layer of talus) may exhibit different thermophysical properties than a more intimate mixture of rock and ice present in a permafrost creep driven system. Thermophysical studies of terrestrial rock glaciers, however, can be difficult due to the small size of these features relative to spatial resolutions of satellite thermal infrared data: often, the rock glacier contributes to only a handful of pixels in either the downslope or transverse direction. By contrast, Martian lobate debris aprons are significantly larger and may occupy tens or hundreds of pixels in a typical THEMIS thermal infrared image.

A case study of an inactive rock glacier located on Lone Mountain (Montana) suggests that ground-based thermal infrared imaging may provide a more appropriate comparison to Martian infrared datasets. The feature examined extends east from the lower slopes of Lone Mountain and can be clearly identified in satellite images. Differences in thermal response to solar heating were identified in infrared images. In Martian datasets, these thermophysical variations are often attributed to differing particle sizes, although this study suggests that surface slopes may provide a significant contribution on this type of feature. Although differences in slope on the scale of the MOLA dataset can be accounted for in analysis of Martian thermal infrared data, small scale slopes such as those likely present on debris aprons may exhibit diagnostic thermophysical variations that provide clues to the internal structure and formation of these features.