This image shows a portion of a lobate debris apron along the bottom of a hill in the Promethei Terra region of Mars. This region contains many such mesas surrounded by lobate debris aprons that are thought to be ice-rich. These aprons have been interpreted as a variety of possible features including rock glaciers, ice-rich mass movements, or debris-covered glacial flows. Recent radar data have shown them to be composed of nearly 100% pure ice. Parallel grooves and ridges indicate the direction of flow.
Both the debris apron and the plains beyond it are blanketed with an ice-rich mantle that is common throughout the Martian mid-latitudes. The mantle deposits are pitted and grooved perhaps due to the sublimation of ice. This mantle is thought to have been deposited as snow around 10 million years ago during a period of high obliquity, when the planet’s axis was more tilted and environmental conditions could have been more conducive to snowfall in these regions.
Several small impact craters are visible on the plains that appear to have been filled with mantling deposits that have subsequently been partially removed. These craters give us clues to the erosional history of the deposit.
Written by: Dan Berman (5 January 2011)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_020319_1470
Image: NASA/JPL/University of Arizona