Relationships Between Subsurface Processes, Eruptive Products and Surface Morphology of Maar-diatreme Volcanoes

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Maars are volcanic craters cut into a pre-eruptive landscape, surrounded by low-profile ejecta or tephra rings. They are among the most abundant volcanoes on Earth, and occur most commonly in volcanic fields where there may be tens or hundreds of individual volcanoes. Maar eruptions present a significant hazard where populated regions overlap with volcanic fields. Because they involve violent explosions caused by mixing of hot magma and groundwater, their eruptions can produce a full gamut of dangerous phenomena including blast waves, pyroclastic flows, widely dispersed ballistic blocks, ash fall and far-travelled fine ash plumes, large-scale subsidence, and volcanic mudflows. Maars and their underlying plumbing structures - diatremes - can also be of economic importance, especially when the erupted magma is diamond-bearing kimberlite. Diatremes commonly resist erosion, and in exhumed landscapes such as the Colorado Plateau they form striking buttes and pinnacles (e.g., Shiprock, New Mexico, and parts of Monument Valley, Arizona). Despite their hazards and economic importance, many questions remain about the subsurface processes beneath maar-diatremes and the relationships of those processes to eruptive phenomena.This project combines field studies at young maar-diatremes with innovative experiments that are intended to mimic, at the scale of meters, the processes that form the volcanoes. Field studies will focus on two young maars, Dotsero (Colorado, age ~4150 yrs) and Nilahue (southern Chile, erupted 1955) where original post-eruptive geometry can be well constrained, the tephra deposits are largely non-indurated and therefore amenable to component and clast shape/texture analysis, and sub-volcanic stratigraphy is well constrained, allowing us to link lithic clasts to their depths of origin. These results will be compared with and interpreted in light of experimental work that will use different configurations of buried explosives in artificial layered "geologies," allowing for characterization of crater geometry and detailed analysis of the composition of ejecta in terms of proportions derived from different depths. Explosions will be monitored with high-speed video, seismometers, and acoustic sensors in order to constrain dynamics, and post-experimental excavation will reveal the "diatremes" that are produced in order to explore the relationship between their structure and ejecta. Together, the field and experimental studies will greatly advance our understanding of maar-diatreme eruptions and the factors that control their hazards and potential economic resources.