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Research — Volcanology




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Cosmogenic dating of young basaltic lava flows
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Cosmogenic dating techniques have been successfully applied to dating of geomorphically-young surfaces, such as glacial moraines, beach terraces, and basaltic lava flows that have intact surface features, and hence have undergone little erosion (e.g. Phillips et al., 1997a and b; Phillips et al, in review, Dunbar and Phillips, 1996; Zreda et al., 1991, 1993; Zreda, 1994; Anthony and Poths, 1992, Laughlin et al., 1994). These techniques rely on measurement of cosmogenic nuclides that begin to build up as soon as a rock is exposed to cosmic rays. Therefore, cosmogenic techniques can be applied to dating of any surface that is composed of material that was not exposed to cosmic rays prior to formation of the surface, and has been exposed more-or-less continuously since. In the case of an extrusive volcanic rock, buildup of cosmogenic nuclides begins when the rock is erupted, so measurement of the ratio of a cosmogenic isotope to a non-cosmogenic isotope can provide an estimate of eruption age (Phillips et al., 1986).

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Ice layers in Antarctica hold secrets to the global climate past
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A team of scientists from the Bureau of Geology has spent many Antarctic summers sampling layers of volcanic ash trapped between layers of ice to learn about climate conditions that existed at the time of the ice deposition. While the volcanic ash can be dated to constrain the time of deposition, oxygen isotope signatures in the ice reveal clues about temperatures that existed as the layers were deposited.

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Tephra layers in Rio Grande Rift Sediments
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The Jemez Mountains volcanic field, in northwestern New Mexico, has been active for at least the past 16.5 million years, and has produced a large number of explosive and effusive volcanic eruptions during that time. Volcanic ash from the Jemez Mountains volcanic field provides a temporal record of the young eruptions from the caldera and many such deposits have been recognized in a number locations in New Mexico. The ash is present as thick deposits near the eruptive source, and as thinner deposits interbedded in ancestral Rio Grande river sediments at greater distances from the vent.

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Uplift of the Tibetan Plateau: Insights from cosmogenic exposure ages of young lava flows
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The Tibetan plateau is a product of the most dramatic tectonic event of recent geological history: the collision of the Indian sub-continent with Eurasia. In spite of the topographic and tectonic implications of the plateau, the mechanisms for its uplift remain controversial. The controversy is in large part a result of poorly constrained uplift history. Types of evidence that have been adduced for the uplift history include paleoecological date, cooling histories of plutonic and igneous rocks, and geomorphic interpretations. Some lines of evidence indicate relatively gradual uplift since the mid-Tertiary, while others support rapid acceleration of uplift during the latest Cenozoic, with the greatest portion during the Quaternary.

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Volcanic record in Antarctic ice
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Volcanic ash and associated aerosol layers in glacier ice offer a uniquely complete record of explosive volcanism. Investigation of these layers, both in bare ice areas of and in ice cores offers insight into eruptive processes, local and regional ice flow processes, and the impact of eruptions on global systems (climate and ozone depletion). The Antarctic ice sheet is an ideal place to preserve a record of volcanic eruptions. The combination of chemical fingerprinting of glass shards, and chemical analysis of volcanic aerosols associated with tephra layers in Antarctic blue ice allows establishment of a high-resolution chronology of local and distant volcanism that can help understand patterns of significant explosive volcanism, atmospheric loading, and climatic effects associated with volcanic eruptions.

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