HR: 16:30h
AN: H52E-03 INVITED     [PDF]
TI: Low Rates of Weathering and Erosion in Wet, Steep, Tropical Highlands
AU: * von Blanckenburg, F
EM: fvb@mineralogie.uni-hannover.de
AF: Institute for Mineralogy, University of Hannover, Callinstrasse 3, Hannover, 30167 Germany
AU: Hewawasam, T
EM: tilak@geo.unibe.ch
AF: University of Berne, Switzerland. Now at Department of Natural Resources, Sabaragamuwa University, Buttala, 91100 Sri Lanka
AB: The Central Highlands of the island of Sri Lanka feature all the ingredients usually thought to promote high rates of weathering: crystalline rocks, warm climate, high rates of precipitation. Also the high relief (steep mountains of up to 2500m altitude) would potentially generate high rates of physical erosion, which in turn promotes weathering by providing fresh mineral surfaces. An analysis of the rates of total erosion, using cosmogenic nuclides, excluding the effects of anthropogenic perturbance [1], was performed on various parts of the landscape (bedrock, surface soil, river sediment). The results suggest that all parts of the Highlands erode at 5-15mm/ky only. Rates of chemical weathering, determined by analysing major cations in river water, further suggest that most of this denudation is chemical. These rates of erosion are amongst the lowest world-wide for any sloping area analysed to date with cosmogenic nuclides. No relationship between climate and erosion is apparent for these areas. For Sri Lanka, we suggest that rock weathering has been low for millions of years due to (a) development of a clay-rich surface layer protecting rocks from corrosive fluids; (b) thick vegetation inhibiting removal of this layer; and (c), most importantly, absence of recent tectonic activity that would rejuvenate the landscape and promote physical erosion. Therefore, climate does not appear to exert controls over rock weathering if active tectonic forcing is absent. 1 T. Hewawasam, F. von Blanckenburg, M. Schaller and W. Kubik, Increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides, Geology 31, 795-600, 2003.
DE: 1800 HYDROLOGY
DE: 1815 Erosion and sedimentation
DE: 9320 Asia
SC: Hydrology [H]
MN: 2003 Fall Meeting