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Accueil du site → Doctorat → États-Unis → 1997 → Evolution of desert colluvial boulder fields, eastern California

Arizona State University (1997)

Evolution of desert colluvial boulder fields, eastern California

Friend, Donald Agar

Titre : Evolution of desert colluvial boulder fields, eastern California

Auteur : Friend, Donald Agar

Université de soutenance : Arizona State University

Grade : Doctor of Philosophy (PhD) 1997

Rhyolite domes formed over a million year continuum in eastern California are used to study the evolution of boulder dominated slopes. Slopes in this study are steep $(\sim25\sp\circ$ to $\sim35\sp\circ)$ and are made of boulder-sized blocks. These slopes include well varnished vertically oriented colluvial deposits that have been likened to relict periglacial stone stripes, or as indicated in this study, are the result of ongoing desert slope processes. The deposits are common throughout the arid southwestern US, but their morphometric character, fabric, and rates of formation have not been assessed systematically. Basic field and isotopic dating methods are combined with two experimental surface dating techniques, cosmogenic chlorine-36 ($\sp36$Cl) and rock varnish microlaminae, to produce a detailed million-year-long slope development history with broad implications in geomorphic theory and environmental issues in deserts. Grain size, grain shape, grain angularity, and slope deposit area do not change significantly from genesis to $\sim$0.5 million years ; trends in the data change markedly after that time. A geomorphic threshold occurs between $\sim$0.5 and $\sim$1 million years as indicated by significant changes in all but grain orientation data. On-going erosion over the million year continuum is indicated by active debris flow features, by terminal Pleistocene ages of microlaminae on all deposits, and by $\sp36$Cl ages that are progressively younger than potassium-argon ages for slope geneses. A classic geomorphic debate is reconsidered : Do slopes retreat in a parallel fashion as postulated by Walther Penck, or do they decline as asserted by William Morris Davis ? Results support Penck. Environmental applications of this research relate to slope erosion studies, and to studies in archeology and paleoclimatology in the southwestern desert region by providing uniquely detailed and controlled studies of slope development where other paleoenvironmental records are abundant. Boulder dominated slopes are found on Yucca Mountain, Nevada, a potential repository for high level nuclear waste. Knowing rates and mechanisms of erosion is critical to the integrity of the storage facility. Boulder slopes are also found in urban areas throughout the southwestern US. In expanding Phoenix, Arizona, construction on boulder dominated slopes is being disturbed by debris flows.

Mots clés : Talus slopes, Geology, geomorphology, rhyolite domes, Geography, Social sciences (more...) Earth sciences

Accès au document : Proquest Dissertations & Theses

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