From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, March 12, 2010
The Collapse of Hebes Chasma, Mars
Link to streaming video: available 03.12.2010 at 8:25am
Dr. Martin Jackson
Senior Research Scientist, Bureau of Economic Geology
Hebes Chasma is a huge closed depression 315 km long and 126 km wide in equatorial Mars. Almost five times deeper than the Grand Canyon of Arizona, Hebes Chasma is one of the deepest canyons on Mars. How was the 105 km3 volume of material removed to form an entirely closed canyon? Photogeologic interpretation and physical modeling indicate that the chasma formed by collapse of a mega-regolith (the surface layer of rubble several kilometers thick) into pits above a regional fracture set in the crust. We suggest that local heating melted ice and dissociated hydrous salts in the mega-regolith. Hydrated sulfate salts have been identified spectrally. The water released drained as brines and entrained particulates through fractures in the chasma floor and into a regional aquifer. The physical models show how collapse may have evolved. The initial evolution of subsidence is preserved at one end of Hebes Chasma. After this initial sagging, the land surface was down-faulted as benches and inward-tilted slabs. Chasma walls collapsed forming landslides having concave-inward headwall scarps. The chasma floor disaggregated by brittle rupture and viscous flow to form chaos terrain. Massive allochthonous flows broke out from the chasma walls and flowed for up to 60 km within the canyon. In places diapirs emerged at the surface. A central plateau called Hebes Mensa bulged up diapirically from depth as it became unroofed by surrounding subsidence. All the displaced material moved towards drainage depressions in the chasma floor. Collapse features, massive flows, and salt diapirs in other canyons in the Valles Marineris region suggest that processes similar to those in Hebes Canyon are widespread, though commonly overprinted by erosion.
The talk is illustrated by time-lapse movies of the models and by spectacular low-oblique color views of the Hebes landforms.