Characterizing boulder deposition to assess rock fall hazard in Upper Pines Campground, Yosemite National Park, CA
Graduation Date
2012
Document Type
Thesis
Program
Other
Program
Thesis (M.S.)--Humboldt State University, Environmental Systems: Geology Option, 2012
Committee Chair Name
R.M. Burke
Committee Chair Affiliation
HSU Faculty or Staff
Keywords
Glacier Point, Rock fall, CA, Yosemite National Park, Glacial, Hazard, KGP, Quaternary, Geomorphology, Alluvial fan, X-ray fluorescence, Geology, Cosmogenic, KHD, Granodiorite, Moraine, XRF, Half Dome, Humboldt State University -- Theses -- Geology
Abstract
Large boulders exceeding 10 m3 in exposed volume are widely scattered throughout the Upper Pines Campground in eastern Yosemite Valley, Yosemite National Park, California. These boulders rest 130-330 m from the base of adjacent talus slopes and lack typical geomorphic expressions of a rock fall deposit in Yosemite Valley. Three modes of transport were considered for deposition of these boulders: (1) glacial deposition during retreat, approximately 15-17 ka, (2) rock fall postdating 15 ka, and (3) fluvial deposition during large scale flooding such as might occur from glacial outburst. The boulder deposit was characterized by field mapping, cosmogenic 10Be exposure ages, x-ray fluorescence (XRF) analysis, and spatial analysis to determine mode(s) of transportation and source. A mean cosmogenic exposure age of 9.6 ± 1 ka (derived from four samples) considerably postdates the Last Glacial Maximum (LGM), suggesting that boulder emplacement does not result from glacial deposition during retreat of ice. XRF results identify Glacier Point Granodiorite boulders transported from ~500 m above Upper Pines on Glacier Point. Based on measured boulder attributes, I suggest that partial iii burial by fan development conceals the original geomorphic expression of the deposit. Discharge and bed stress modeling indicate that flooding was not capable of moving the boulders to their current location. Thus, I interpret that the boulders were deposited as the result of a single rock fall (or possibly rock avalanche) event that originated ~500 m above Upper Pines Campground on Glacier Point at approximately 9.6 ± 1 ka.
Recommended Citation
Cordes, Shaun Emmett, "Characterizing boulder deposition to assess rock fall hazard in Upper Pines Campground, Yosemite National Park, CA" (2012). Cal Poly Humboldt theses and projects. 996.
https://digitalcommons.humboldt.edu/etd/996
https://scholarworks.calstate.edu/concern/theses/ws859j082