Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21a1316p&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P21A-1316
Physics
6017 Erosion And Weathering, 6020 Ices, 6045 Physics And Chemistry Of Materials, 6055 Surfaces
Scientific paper
Images returned by the Cassini-Huygens mission reveal evidence for widespread fluvial incision in the polar regions of Titan. Dendritic channel networks draining to large lakes and the absence of cratering suggest active incision into Titan's water-ice bedrock surface. Previous work using the saltation-abrasion bedrock incision model suggests that a terrestrial channel transposed to Titan conditions would incise at remarkably similar rates, because the effects of Titan's lower gravity and less-dense sediments are offset by a much lower resistance to abrasion for ice than rock of similar strength. Here we report new laboratory measurements of ice erosion by low-velocity sediment impacts, part of a larger study investigating the temperature dependence of the material properties that control ice erodibility. We measure the energy required to erode a unit volume of ice using drop tests, in which a 110-150 g ice clast falls 5-10 cm onto a 20 cm diameter ice disk, and differences in mass and measurements of ice density are used to calculate the volume eroded. We construct the 10cm thick ice disks using 2-4 mm seed crystals and near-freezing distilled water. After freezing at 253 K a disk is placed in the bottom of a steel cylinder surrounded by dry ice and liquid nitrogen is pumped into the cylinder from below, chilling the ice to near-Titan temperatures for several hours but never submerging the samples (all drop test trials are completed in air). Our preliminary drop test results show that 4 J and 25 J are required to erode 1 cm3 of ice at temperatures of 205 K and110 K respectively, suggesting that ice may be no more than 2-3 times more erodible than previously-tested rocks of similar tensile strengths. A key limitation of this experimental method is the small size of our target disks, which fail catastrophically by through-cracking after several hundred drops. To avoid through-cracking and obtain direct measurements of ice surface erosion, we are preparing new experiments using a large ice block (~1.25x105 cm3) enclosed in an insulated test chamber, and a laser topographic scanning system. The drop-test results will then be used to design ice-flume experiments in a walk-in freezer to investigate controls on rates of ice incision by mobile sediments and the morphodynamics of incising ice channels.
Collins Geoffrey
Polito P. J.
Sklar L. S.
Zygielbaum B. R.
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