Modulation of erosion on steep granitic slopes by boulder armoring, as revealed by cosmogenic Al-26 and Be-10

Citation
De. Granger et al., Modulation of erosion on steep granitic slopes by boulder armoring, as revealed by cosmogenic Al-26 and Be-10, EARTH PLAN, 186(2), 2001, pp. 269-281
Citations number
51
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
EARTH AND PLANETARY SCIENCE LETTERS
ISSN journal
0012-821X → ACNP
Volume
186
Issue
2
Year of publication
2001
Pages
269 - 281
Database
ISI
SICI code
0012-821X(20010330)186:2<269:MOEOSG>2.0.ZU;2-I
Abstract
Cosmogenic Al-26 and Be-10 in quartz from boulders, bedrock and sandy sedim ent from 21 small watersheds in the Diamond Mountains batholith, CA, USA, a nd two small watersheds from the nearby Fort Sage Mountains confirm that ex posed granitic bedrock and boulders erode more slowly than the catchments i n which they are found. Exposed bedrock and boulders are more abundant on s teep slopes and may play an important role in regulating mountain erosion r ates. Rapid transport of fine sediment on steep slopes exhumes resistant co restones which accumulate on the surface. The resulting boulder lag apparen tly shields the underlying soil and bedrock from erosion, even when the bed rock is deeply weathered and friable. Where steep slopes have an abundant b oulder lag, they erode as slowly as gentler slopes nearby. In contrast, ste ep slopes lacking a boulder lag erode much more quickly than gentle slopes. Boulder armoring can modulate hillslope erosion such that erosion rates of summits, steep mountain flanks, and gentle footslopes are indistinguishabl e, thus permitting local relief and steep mountain slopes to persist for lo ng periods of time. (C) 2001 Elsevier Science B.V. All rights reserved.