CaltechAUTHORS
  A Caltech Library Service

Quantitative morphologic analysis of boulder shape and surface texture to infer environmental history: A case study of rock breakdown at the Ephrata Fan, Channeled Scabland, Washington

Ehlmann, Bethany L. and Viles, Heather A. and Bourke, Mary C. (2008) Quantitative morphologic analysis of boulder shape and surface texture to infer environmental history: A case study of rock breakdown at the Ephrata Fan, Channeled Scabland, Washington. Journal of Geophysical Research F, 113 (F2). Art. No. F02012. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20121015-114403969

[img]
Preview
PDF - Published Version
See Usage Policy.

1017Kb

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20121015-114403969

Abstract

Boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion, transport, and weathering. At present, morphologic information at the boulder scale is underutilized as a recorder of environmental processes, partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets. We develop such a parameter set, incorporating a range of measures of boulder form and surface texture. We use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser-scanned molds. The parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the Channeled Scabland, Washington: (1) basalt outcrop talus; (2) flood-transported boulders recently excavated from a quarry; and (3) flood-transported boulders, extensively weathered in situ on the Ephrata Fan surface. Size and shape data were found to distinguish between flood-transported and untransported boulders. Size and edge angles (∼120°) of flood-transported boulders suggest removal by preferential fracturing along preexisting columnar joints, and curvature data indicate rounding relative to outcrop boulders. Surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments. Past signatures diagnostic of flood transport still persist on surface boulders, despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ. Further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2007JF000872DOIUNSPECIFIED
http://www.agu.org/pubs/crossref/2008/2007JF000872.shtmlPublisherUNSPECIFIED
ORCID:
AuthorORCID
Ehlmann, Bethany L.0000-0002-2745-3240
Additional Information:© 2008 American Geophysical Union. Received 11 July 2007; accepted 1 February 2008; published 6 May 2008. Special thanks go to John Meneely at Queen’s University Belfast for use of the 3-d digital scanner. Bernie Smith and Dave Thomas provided helpful suggestions on early versions of this work. Jeffrey Lancaster and Eric Troffkin provided timely advice on techniques for plaster molding, Bill Hutson provided valuable insights on multivariate statistics, while Phil Jackson, Norm Charnley, and Robin Rotman assisted in the preparation and interpretation of thin sections. This work was partly funded by NASA Planetary Geology and Geophysics grant NNG05GJ91G and by the Rhodes Trust.
Funders:
Funding AgencyGrant Number
NASA Planetary Geology and GeophysicsNNG05GJ91G
Rhodes TrustUNSPECIFIED
Subject Keywords:weathering; basalt; Channeled Scabland; quantitative morphology; fractal analysis; morphometric classification
Issue or Number:F2
Record Number:CaltechAUTHORS:20121015-114403969
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20121015-114403969
Official Citation:Ehlmann, B. L., H. A. Viles, and M. C. Bourke (2008), Quantitative morphologic analysis of boulder shape and surface texture to infer environmental history: A case study of rock breakdown at the Ephrata Fan, Channeled Scabland, Washington, J. Geophys. Res., 113, F02012, doi:10.1029/2007JF000872.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34897
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:15 Oct 2012 20:28
Last Modified:09 Mar 2020 13:18

Repository Staff Only: item control page