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Science 9 December 2005:
Vol. 310. no. 5754, pp. 1668 - 1670
DOI: 10.1126/science.1118519
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Reports

Rapid Glacial Erosion at 1.8 Ma Revealed by 4He/3He Thermochronometry

David L. Shuster,1*{dagger} Todd A. Ehlers,2 Margaret E. Rusmoren,3 Kenneth A. Farley1

Alpine glaciation and river incision control the topography of mountain ranges, but their relative contributions have been debated for years. Apatite 4He/3He thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern Coast Mountains of British Columbia, Canada. Five proximate samples require accelerated denudation of the Klinaklini Valley initiating 1.8 ± 0.2 million years ago (Ma). At least 2 kilometers of overlying rock were removed from the valley at ≥5 millimeters per year, indicating that glacial valley deepening proceeded ≥6 times as fast as erosion rates before ~1.8 Ma. This intense erosion may be related to a global transition to enhanced climate instability ~1.9 Ma.

1 Division of Geological and Planetary Science, California Institute of Technology, 100 23, Pasadena, CA 91125, USA.
2 Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
3 Department of Geology, Occidental College, Los Angeles, CA 90041, USA.

* Present address: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.

{dagger} To whom correspondences should be addressed at Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA. E-mail: dshuster{at}bgc.org

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