Detail An analysis of glass weathering, El Malpais National Monument, New Mexico, USA Bibliografi Author: Gordon, Steven Joseph ; Dorn, Ronald I. (Advisor) Topik: PHYSICAL GEOGRAPHY|GEOLOGY Bahasa: (EN )    ISBN: 0-599-38635-5     Penerbit: Arizona State University     Tahun Terbit: 1999     Jenis: Theses - Dissertation Fulltext: 9937404.pdf (0.0B; 0 download) Abstract An understanding of the nature and rate of weathering of basaltic glass in a natural environment over thousands of years timescales is important to the study of long-term climate regulation, safe storage of high level nuclear waste glasses, and other Earth processes. Field-based weathering rates of basaltic glass that rely on collection of samples from a single basalt flow may be influenced by many factors that vary across the flow. This dissertation calculates a field-based rate of basaltic glass weathering and investigates the effects of elevation, glass chemistry, lichen growth, and shape of porosity on that rate. Digital image processing of backscattered electron micrographs was employed to identify weathering-created porosity in the interstitial glass. The mean rate of weathering of glass in the McCartys flow is 2.08% per thousand years. This rate is approximately 103 times slower than comparable laboratory rates, which can be partially accounted for by temperature, moisture, and time differences between laboratory and field environments. The rate increases with an increase in elevation, suggesting that the weathering/elevation relationship is the result of the competing effects of mean annual temperature with moisture availability, vegetation, and other factors that increase with elevation. Variation in chemical composition of the glass samples has no effect on the weathering rate. Small variations in chemical composition of glass within a single lava flow can safely be ignored for the purposes of determining weathering rate. Weathering rates of basaltic glass are enhanced by the presence of lichens by at least 1.7x over rates of dissolution in the absence of them. The localized effect of lichens to near-surface weathering makes this effect scale-dependent, with minimal influence on the scale of mass lost from a lava flow but influential on the scale of thin layers of glass on basalt flows. Porosity from glass weathering takes three forms: small, compact holes, thin, elongated lines, and larger areas. Quantitatively, the porosity is neither exceptionally compact nor elongated. Elongation does not depend on elevation change nor changes in the chemical composition of the glass. Mean elongation and edge values, not including the smallest pores, reveal that porosity in glass is neither overly rough- nor smooth-edged, and independent of elevation and chemistry. Opini Anda Klik untuk menuliskan opini Anda tentang koleksi ini! Lihat Sejarah Pengadaan  Konversi Metadata   Kembali

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