Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p42b..03h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P42B-03
Mathematics
Logic
[5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Channels originating at or near the margins of the continuous ejecta blanket of the youthful (Late Hesperian/Early Amazonian) 140 km-diameter Hale Crater have previously been attributed to melting of ice in the target material by superheated impact melt or remobilization of saturated ejecta. However, the presence of channels in the vicinity of Hale that do not originate on or at the margins of the ejecta blanket but are similar in morphology to those that do may suggest that channel formation at Hale was triggered by seismic energy from the impact. A key example lies at 33.0°S, 39.7°W, ~250 km northwest of Hale, where a small scabland (e.g. morphologies similar to the Channeled Scabland of the Columbia River Plateau, Washington) is observed. The scabland is located too far from the Hale impact to be explained by thermal melting of subsurface ice during the impact event. The channels are not associated with the Hale ejecta blanket, and are therefore not related to dewatering processes. The channels appear to be geologically young, with few superposed craters. Distinct depositional facies are observed; the channels terminate in a topographic depression in which the channel deposits have ponded. These deposits also have very few superposed craters. Aeolian bedforms are observed atop the deposits, potentially a lag of coarse-grained sand from within the deposits. These bedforms are confined to the deposit surface and are not observed elsewhere in the area. We propose that this “mini-scabland” was formed by the release of shallow groundwater due to seismic energy from the Hale impact. Seismic energy from earthquakes can lead to groundwater release via ejection of confined groundwater and/or upwelling of an unconfined shallow water table. In the former case, the water is confined by an impermeable layer and is typically released by jetting or spouting, resulting in fissures and/or mounds referred to as mud volcanoes. The latter case produces widespread non-eruptive water-sediment flows due to a rising water table and soil liquefaction. Evidence for liquefaction associated with terrestrial impact events has been documented. Seismic energy can trigger groundwater flow at great distances; the 1964 Great Alaskan Earthquake triggered the ejection of water-saturated sediments > 400 km from the epicenter. The lack of fissures and cones in the vicinity of the mini-scabland suggests that water was released non-explosively, implying that the groundwater involved in carving the channels was likely very shallow in the subsurface and was unconfined. The presence of groundwater in the area of Hale at various times in martian history is suggested by the occurrence of a number of gullies—hypothesized to have formed from discharges from shallow aquifers—within Hale and in surrounding craters and nearby Nirgal Vallis, which appears to have formed due to groundwater sapping based on its morphology. The channels at Hale may hence give credence to the shallow aquifer model for martian gully formation.
Harrison Tanya N.
Kennedy Robert M.
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