Aspects of alluvial fan shape indicative of formation process: A case study in southwestern California with application to Mojave Crater fans on Mars

Abstract

Longitudinal profiles from six alluvial fans surveyed in southwestern California have quantitative attributes that can distinguish formation processes. The radial slope of fans where debris flow processes dominated is constant while fluvially-fed fans have a concave-upward shape. We find the power law regression of upstream slope-distance profiles is the preferred approach for assessing concavity. Concavity index, the exponential determined via power law regression analysis, is an accurate reflection of the magnitude of the concavity and thus a qualitative measure of the relative influence of fluvial processes on the fan. Fan length and surface gradient are inversely correlated: debris flow fans are shorter and steeper (>15°) than their fluvial counterparts. The results of this investigation provide criteria to evaluate hypothesized formation processes and provide constraints on the amount of fluid and timescales involved in the generation of comparably-sized fans within Mojave Crater, Mars. Copyright 2006 by the American Geophysical Union.