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Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces

Kendrick, Katherine J. and Partin, Camille A. and Graham, Robert C. (2016) Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces. Journal of Geology, 124 (4). pp. 529-539. ISSN 0022-1376. http://resolver.caltech.edu/CaltechAUTHORS:20160804-082406738

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Abstract

Rock surface erosion by wildfire is significant and widespread but has not been quantified in southern California or for chaparral ecosystems. Quantifying the surface erosion of bedrock outcrops and boulders is critical for determination of age using cosmogenic radionuclide techniques, as even modest surface erosion removes the accumulation of the cosmogenic radionuclides and causes significant underestimate of age. This study documents the effects on three large granitic boulders following the Esperanza Fire of 2006 in southern California. Spalled rock fragments were quantified by measuring the removed rock volume from each measured boulder. Between 7% and 55% of the total surface area of the boulders spalled in this single fire. The volume of spalled material, when normalized across the entire surface area, represents a mean surface lowering of 0.7–12.3 mm. Spalled material was thicker on the flanks of the boulders, and the height of the fire effects significantly exceeded the height of the vegetation prior to the wildfire. Surface erosion of boulders and bedrock outcrops as a result of wildfire spalling results in fresh surfaces that appear unaffected by chemical weathering. Such surfaces may be preferentially selected by researchers for cosmogenic surface dating because of their fresh appearance, leading to an underestimate of age.


Item Type:Article
Related URLs:
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http://dx.doi.org/10.1086/686273DOIArticle
http://www.journals.uchicago.edu/doi/10.1086/686273PublisherArticle
Additional Information:© 2016 by The University of Chicago. Manuscript received June 24, 2015; accepted February 10, 2016; electronically published May 23, 2016. This study benefited from early reviews by D. Ponti and K. Knudsen (USGS) and B. Goforth (California State University, San Bernardino). Thoughtful reviews were also provided by A. Gillespie (University of Washington) and G. Girty (San Diego State University).
Record Number:CaltechAUTHORS:20160804-082406738
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160804-082406738
Official Citation:Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces Katherine J. Kendrick, Camille A. Partin, and Robert C. Graham The Journal of Geology 2016 124:4, 529-539
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69430
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Aug 2016 21:39
Last Modified:04 Aug 2016 21:39

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