Concentric Crater Fill Research Articles

Subsurface investigation of a rock glacier using ground‐penetrating radar: Implications for locating stored water on Mars

The discovery of rock glacier‐like features on Mars suggests the presence of flowing, or once‐flowing, ice‐rock mixtures. These landforms, which include lobate debris aprons, concentric crater fill, and lineated valley fill, hold significant promise as reservoirs of stored water ice that could be used as fuel sources for human exploration of Mars and provide a frozen record of the climatic history of the planet. To understand the deformation and distribution of ice within these landforms, fundamental descriptions of their internal structure and development are required. To this end, a ground‐penetrating radar investigation was initiated using rock glaciers in the San Juan Mountains of Colorado as surrogates for similar Martian landforms. Results obtained from one of these rock glaciers show that the interior of the landform is composed of a layered permafrost matrix of ice, sediment, and ice lenses that comprise thicker depositional units formed through high‐magnitude debris falls. Folds in the uppermost layers correspond to the surface expression of ridges and furrows, suggesting that compressive stresses originating in the accumulation zone are transmitted downslope through the rock glacier. Rock glacier features on Mars may also consist of layered permafrost, which would suggest a history of development involving seasonal frost accumulation and/or water influx from below. In terms of water storage within Martian analogs, consideration must include the possibility that some water ice may be stored in relatively pure form within lenses and vein networks such as observed in the surrogate rock glacier of this study.

Ice flow and rock glaciers on Mars

Several geologic features suggest the presence of rock glaciers on the surface of Mars. These features include lobate debris aprons, concentric crater fill and lineated valley fill. The lateral extent of these rock glaciers can range from 5 km to over 20 km. A simple time‐marching model is developed and used here to demonstrate the ability of ice and ice‐rock mixtures to flow under Martian conditions. For temperatures lower than about 220 K, even pure ice becomes too rigid to flow and a glacier 5 km long could not have formed. Results from this model indicate temperatures 20 to 40 K higher than present average midlatitude temperatures (210 K), an ice content of no less than 80%, and a net accumulation rate of at least 1 cm year−1 are required to produce rock glaciers of the size seen on Mars.