HR: 0800h
AN: H11B-0478    [Abstracts]
TI: Clast Breakdown on Desert Surfaces by Differential Insolation of Cracks
AU: * Moores, J E
EM: jmoores@lpl.arizona.edu
AF: University of Arizona, Department of Planetary Sciences, 1629 E University Blvd, Tucson, AZ 85721-0092, United States
AU: Pelletier, J D
EM: jdpellet@email.arizona.edu
AF: University of Arizona, Department of Planetary Sciences, 1629 E University Blvd, Tucson, AZ 85721-0092, United States
AU: Smith, P H
EM: psmith@lpl.arizona.edu
AF: University of Arizona, Department of Planetary Sciences, 1629 E University Blvd, Tucson, AZ 85721-0092, United States
AB: In the Southwest US, cracks in surface clasts have a preferred orientation independent of rock fabric, rock shape and local conditions. Differential insolation of incipient cracks of random orientations provides an explanation of this preferred orientation through removal of moisture held in the crack. A study of differential insolation of cracks of different orientations at 35 north latitude was undertaken using a numerical radiative transfer code and idealized crack geometry. The amount of energy reaching the bottom of each crack was calculated at five minute intervals over the day for several days of the year to determine hourly, daily, seasonal and annual deposition of energy depending only on crack orientation and depth. By adding to this a formulation in which only crack orientations which effectively shield their interiors and minimize their water loss are able to grow, the observed pattern of cracks is reproduced, including both expressed modes and their deviations from pure North-South and East-West behavior. Given this formulation, the important timescale for water retention is the annual average insolation which is associated with both modes of the aligned cracks while the daily recharge by summer monsoon rains is responsible for the observed deviations of these modes. Thus, both the annual average insolation and the daily pattern of rainfall are recorded in the cracking patterns of surface rocks in the Southwest.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1847 Modeling
DE: 3359 Radiative processes
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2007 Fall Meeting