Impact of consecutive extreme rainstorm events on particle transport: Case study in a Sonoran Desert range, western USA

Quantifying erosion rates in different landscape settings provides insight into how landforms change under different climatic, tectonic and anthropogenic influences. Sediment traps designed to capture grus detached from granitic hill crests of an arid Sonoran Desert mountain range were placed prior to every precipitation event over a three-year period, just above rills that drain areas between 18 and 68m². The slopes are underlain by moderately to strongly weathered granitic rocks to a depth of about a meter. Within this 3-year window, a 1000-year precipitation event followed 27days later by a 500-year event detached granitic grus in amounts far greater than previous storms, capturing between 22× and 63× the average amount transported in the previous 59 rain events - indicating the non-linear nature of the response of grus detachment to precipitation intensity. Considering every precipitation event over a 3-year period, no detachment occurred from events with less than 2mm of total rainfall, and only minimal erosion occurred from rainfall events with totals between 2 and 10mm with durations typically less than 30min. Detachment increased greatly with rain intensities of 36mm/h or more. Grus detachment from these arid crests increases with drainage area, a higher percentage of exposed soil, and steeper slopes. ⁸⁷Sr/⁸⁶Sr ratios reveal that suspended sediment transported from hill crest to trap derives from recycled dust and not the local granite bedrock.