Gulley Incision Into Basaltic Tephra Deposits And Implications For Mars Valley Network Formation

Details Gulley Incision Into Basaltic Tephra Deposits And Implications For Mars Valley Network Formation Gulley Incision Into Basaltic Tephra Deposits And Implications For Mars Valley Network Formation

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusm.p41a..06c&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #P41A-06

Mathematics

Logic

1825 Geomorphology: Fluvial (1625), 4558 Sediment Transport (1862), 5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 5470 Surface Materials And Properties

Scientific paper

It's clear from geologic features such as the Tharsis volcanoes, analyses of the SNC meteorites, multispectral data from orbiting spacecraft, and in situ measurements made by landers that the martian surface is composed primarily of basalt. Spacecraft data also suggest that this basaltic surface has been broken down into friable materials produced by weathering, impact cratering and explosive volcanism. We have begun a series of analyses in the Ka'u Desert of Hawaii to better understand the environmental conditions necessary to initiate surface runoff and channel incision in brecciated basaltic materials similar to the martian surface. We used Differential GPS surveys to measure the cross-sections and slopes of gullies that have incised into the Keanakako'i tephra deposit located on the eastern margin of the Ka'u Desert near the rim of Kilauea volcano. We conducted grain-size analyses of channel sediments and made estimates of flow depths during peak discharge based on field evidence. Wherever possible, we also analyzed the stratigraphy of fluvial sedimentary deposits emplaced over basaltic lava flows of known ages and determined the number of flood events associated with these materials. Our results suggest that many of the larger gullies have peak discharges of approximately 100 m3/s, and that flood events occur once every 3 years on average. Climate data for the region indicate that runoff within the gullies occurs during severe thunderstorms. Although rare, these storms are intense and long-lived, typically producing rain over an 18-48 hour period at a rate of upwards to 1-2 inches per hour. Field observations suggest that equally intense, but short-lived storms (e.g., a few hours) produce no appreciable runoff. Essentially the high infiltration capacity and porosity of the Keanakako'i tephra effectively inhibits runoff except in the most extreme environmental conditions. This implies that the storms on Mars that created the valley networks were comparable to some of the worse storms on Earth, or, possibly, the release of water from snowmelt was somehow catastrophic.

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