Rock avalanche deposits store quantitative evidence on internal shear during runout. Issue 17 (9th September 2017)

• Record Type: Journal Article
• Authors: Zhang, M.; McSaveney, M. J.
• Is Part Of: Geophysical research letters. Volume 44:Issue 17(2017)
• Page Start: 8814
• Page End: 8821
• Publication Date: 2017-09-09
• Subjects: rock avalanche -- ring‐shear test -- grain fragmentation -- shear rate -- normal stress -- shear strain; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL073774
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We investigated the quantitative effect of internal shear on grain breakage during rock avalanche runout, by means of 38 ring‐shear experiments on identical sand samples at different normal stresses, shear strains and shear strain rates. We compared sample grain‐size characteristics before and after shearing. We found that grain size decreased with increase in normal stress and shear strain. Reduction in grain size was inferred to occur through grain breakage associated with grain interactions in strong force chains during strain. The results were consistent with observations of both inverse‐grading structure in deep rock avalanche exposures, and fining and grading of particles with increasing rock avalanche travel distance. Our study suggested that with appropriate calibration, variations in grain‐size distributions within a rock avalanche deposit would provide quantitative information on the distribution of internal shear during its runout. Key Points: Internal shear of granular debris during rock avalanche runout was simulated in a simple ring‐shear device Normal stress and shear strain were key factors controlling grain‐size reduction in the simulation Grain‐size variations in rock avalanche deposits hold quantitative information about internal shear during runout