Causes and Consequences of Holocene Mafic Explosive Volcanism in Central OR

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Central Oregon has been the site of numerous volcanic eruptions in the past 10,000 years from both Newberry Volcano and vents distributed throughout the central Oregon Cascades. Most of these eruptions have produced basaltic lava flows and cinder cones and it is suspected that many of the eruptions also created substantial eruption columns that could have distributed small amounts of volcanic ash over large regions. As the population of the largest city in central Oregon, Bend, has increased by 50% since 2000 (the population is currently ~ 75,000) and as Bend lies east (downwind) of the Cascades and is constructed on distal lava flows and scoria cones from Newberry Volcano (designated a ?very high threat? volcano by the USGS), it is important to understand the scope of potential future hazards posed by ash-producing eruptions that could affect air traffic, recreation, and agriculture. To insure that this work is available to local populations, they will coordinate with both U.S. Geological Survey and U.S. Forest Service scientists and interpreters to translate findings and improve outreach efforts related to all aspects of volcanism in central Oregon. To improve volcanic hazard assessment in central Oregon, it is proposed to study deposits produced by several different eruptions, many of which have occurred over the past 2000 years. Specifically, they will map and sample deposits from (1) young scoria cones north of North Sister stratovolcano (Yapoah, Four-in-One, and Collier Cone); (2) the young shield volcano Belknap Crater; and (3) the most recent basaltic eruptions of Newberry Volcano, erupted along its northwest rift zone about 7000 years ago. One of the goals is to determine both the thickness and distribution of ash and scoria deposits, as these pose the primary hazard from future eruptions in the region, and the volatile (water and carbon dioxide) content of the magma, to determine the extent to which the volatile content of the rising magma controls the eruptive style (explosive or effusive, that is, dominated by ash deposits or lava flows). In particular, it is believed that this work will provide insights into conditions that cause basaltic magma to erupt explosively. Another goal will be to study more distal ash deposits using sub-alpine lake cores; this work will be collaborative with colleagues from the Geography department, as identification of ash deposits in these cores will allow them to assess the vegetative response to eruptions over the past 2000 years. Taken as a whole, the proposed work is unique in its approach in that they hope to combine methods from petrology (by studying magmatic volatiles and tephra textures) and physical volcanology (by studying the nature of the tephra deposits) to develop of comprehensive picture of the magmatic systems that drive monogenetic or small polygenetic mafic eruptions.