My name is Susanne McDowell. I’m currently a third-year Ph.D. student in the Earth and Environmental Sciences department at Vanderbilt University (Nashville, TN).

Southern Brazil, June 2011

Background:

Growing up, I never imagined that I would become a scientist. I had visions of writing the Great American Novel, serving as a foreign correspondent for a major newspaper, or playing in the first violin section of an orchestra. Science, I told people, just wasn’t my “thing.” My outlook changed during my freshman year of college when I signed up for Introductory Geology in order to meet a core course requirement. Almost immediately, I was drawn to the geological sciences. I came to see rocks as the Earth’s historical archives: each one has a story to tell about the processes that have shaped the planet, and some of those stories are millions or even billions of years old.

On a field trip to the Appalachians with the Vanderbilt geology department, September 2000

After graduating from the University of North Carolina with my master’s degree in 2004, I left academia for several years to start a family and teach courses online. But I missed interacting with students in person; I also missed research. I was drawn to the Environmental Sciences Ph.D. program at Vanderbilt University in part by the opportunity to work with internationally-respected Earth scientists with a wealth of teaching, mentoring, and research experience. I was also drawn by the chance to study large continental volcanic systems (including those that produce supereruptions!) using both field and laboratory techniques.

Geology excites me because it offers abundant opportunities for exploration, sleuthing, and
discovery. We look for clues in rocks and other Earth materials to help unravel the mysteries of its past and to better understand modern processes, especially those that occur over timescales greater than human lifespans.

Research Focus:

My research focus is felsic magmatic systems, including systems that produce supereruptions. I use a combination of geochemistry, geochronology (age dating), field observations/mapping, and petrographic analysis to delve into questions like…

  • …how does the shallow crust accommodate magma reservoirs, particularly those that produce supereruptions (>450 km3 magma)?
  • …over what timescales do magma bodies of various sizes form, how long do they last, and if they erupt, what triggers their eruption? How are silicic magmas, especially high-silica magmas (>75 wt% SiO2), produced?
  • …what are the relationships between plutonic rocks and contemporaneous volcanics?
  • …how does supereruptive magmatism compare to “normal” magmatism, and how do supereruptive magmas/processes relate to their less dramatic magmatic counterparts?

Current Research Projects:

My dissertation research focuses on two silicic plutonic-volcanic systems. The first is in the Colorado River Extensional Corridor of Arizona, where late Cenozoic crustal extension has exposed a series of ~12-20 Ma volcanic and intrusive assemblages. Here the Miocene rock record includes an extensive supereruption-generated pyroclastic flow deposit (known as an ignimbrite) and the caldera from which it erupted.

Geologizing in the field with my dissertation advisor, Calvin Miller, March 2012

The second is in southern Brazil, where a discontinuous string of ~540-600 million year old granites, silicic lavas, and pyroclastic deposits extends northeastward from the border of Uruguay for hundreds of kilometers.

Southern Brazil (Sao Paulo state)

For both projects, I employ a combination of bulk rock and mineral geochemistry, bulk rock and mineral isotopic analysis, and U-Pb zircon geochronology. One of my ancillary goals is to evaluate results from the three major methods of zircon dating (thermal ionization mass spectrometry, secondary ion mass spectrometry, and laser ablation inductively coupled plasma mass spectrometry) and assess how these techniques compare with, and complement, one another in the study of silicic magma systems.