School of Earth Sciences and Environmental Sustainability

My research into eruption and emplacement processes of pyroclastic flows and surges has focused on large-volume ignimbrites in Argentina and Italy and on maar volcanoes in Arizona, Alaska, and Italy.

The driving question is how do these pyroclastic gravity currents form and move. Because we really only have deposits to work with, my research designs aim to cut through the "filter" of the deposition to get at what the current looked and acted like , at least in the lower part, near the depositional zone. I commonly use careful field work, petrography (optical and electron), and paleomagnetism (especially anisotropy of magnetic susceptibility) as tools. My petrologic interests currently center on the origins of the Hopi Buttes (NE Arizona) monchiquitic and nephelinitic magmas. I have an isotope clean lab and am a co-PI on our new multi-collector ICP mass spectrometer, on which we can do much of the analysis.

I am also currently working on the interaction between humans and the youngest volcanism in the Southwestern USA, concentrating on the ~1050 AD Sunset Crater eruption near Flagstaff and the Little Springs eruption (dated between 1100 and 1200 AD). Both eruptions had profound effects on the people living there then, so I am working with an archaeologist and other geologists to understand how the environment changed.

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My previous research has included the effects of acid rain, volcanic emissions, and sulfide mineral deposits on terrestrial and aquatic ecosystems in North America, South America, and Scandinavia, and on the biogeochemistry of Southwestern US rivers.

I now work with the Grand Canyon Monitoring and Research Center of the U.S. Geological Survey performing biogeochemical and geomorphological research and monitoring to aid in adaptive management of the Glen Canyon Dam and the Colorado River’s flow through Grand Canyon.  I have a long-term interest in the impacts of acid deposition, acid mine drainage, and acid rock drainage on the alpine and subalpine ecosystems of the Rocky Mountain west, particularly Southwestern Colorado. I’m also interested in the controls on and dynamics of travertine deposition in rivers of the Southwest.

I am interested in developing new ways to investigate the record of fluid flow in fault systems in order to understand the plumbing of fluid systems and how fluid-rock interactions affect rock properties over short and long time periods.

The results of this research bears on the evolution of fluid circulation in the crust, deformation mechanisms and seismicity at active margins, redistribution of elements in the marine system, and perhaps on the evolution of life in extreme environments. My students, colleagues, and I investigate these processes using a variety of analytical techniques. Each project involves a substantial component of:

• field mapping
• rock characterization
• sample collection—using the good old Brunton compass
• high-precision mapping
• tools for field measurement of rock permeability.

We characterize the cements and fabrics of the samples using petrography and image analysis including scanning electron microscopy and associated imaging techniques. We try to unravel fluid flow histories and the evolution of fluid sources by combining petrographic studies with mass spectrometry, focusing on the trace-element, stable, and radiogenic isotope geochemistry of precipitates left behind by fluids passing through the system.

My current areas of research are carbonate cements and veins preserved in active faults in the Cascadia subduction zone, deformation bands and petroleum migration along the Newport- Inglewood fault zone in southern California, a Paleocene cold seep deposit (chemoherm) on the west side of the San Joaquin Valley, California, and fault systems in coarse-grained clastic rocks of the Colorado Plateau. In addition to basic scientific research, I am involved in projects to improve and increase Earth science education at the K-16 level.