Secondary electron imagery of microcracks and hackly fracture surfaces in sand-size clasts from the 1980 Mount St. Helens debris-avalanche deposit: Implications for particle-particle interactions

Abstract

Research Article| March 01, 1991 Secondary electron imagery of microcracks and hackly fracture surfaces in sand-size clasts from the 1980 Mount St. Helens debris-avalanche deposit: Implications for particle-particle interactions Jean-Christophe Komorowski; Jean-Christophe Komorowski 1Department of Geology, Arizona State University, Tempe, Arizona 85287-1404 Search for other works by this author on: GSW Google Scholar Harry X. Glicken; Harry X. Glicken 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar Michael F. Sheridan Michael F. Sheridan 1Department of Geology, Arizona State University, Tempe, Arizona 85287-1404 Search for other works by this author on: GSW Google Scholar Geology (1991) 19 (3): 261–264. https://doi.org/10.1130/0091-7613(1991)019<0261:SEIOMA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jean-Christophe Komorowski, Harry X. Glicken, Michael F. Sheridan; Secondary electron imagery of microcracks and hackly fracture surfaces in sand-size clasts from the 1980 Mount St. Helens debris-avalanche deposit: Implications for particle-particle interactions. Geology 1991;; 19 (3): 261–264. doi: https://doi.org/10.1130/0091-7613(1991)019<0261:SEIOMA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Scanning electron microscope images of 0.5-1 mm clasts from the volcanic debris- avalanche deposit of the May 18, 1980, eruption of Mount St. Helens display two features not previously described in other volcaniclastic deposits: microcracks and hackly fracture surfaces.Microcracks characterize pyrogenic crystals (pyroxenes, amphibole, plagioclase, and quartz)as well as dacitic, andesitic, and basaltic vitric rock fragments from the avalanche debris.Microcracks commonly resemble cracks separating blocks with a jigsaw fit, as observed on an outcrop scale. Many microcracks (0.5-5 μm) show evidence of lateral displacement, separation, and intersecting relations. In addition, projecting surfaces of fragments exhibit well-developed backly texture defined by crushed areas on the surface. These areas form a dense network of smooth and concave truncating fracture surfaces that resemble fish scales. Regions of low topography on the surface of rock fragments show virtually no evidence of breakage, cracking, or abrasion in contrast with topographically higher and protruding regions. Different mechanisms appear to be responsible for the development of these two surface textures. The microcracks may have resulted from the repeated propagation of compression-rarefaction stress waves that were generated close to the mountain as it disintegrated and the initial slide blocks and later debris avalanche moved over rough topography. Hackly fractures most likely resulted from the pounding of grain-surface projections by repeated high- pressure contacts of grains that remained in close proximity during transport within the debris avalanche. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.