Giant radial dike systems that on average are several hundred kilometers in radius can be found on Earth, Venus and Mars. To date, however, it has been unclear how these impressive volcanic features might originate. For such systems to form, massive quantities of magma ascending from the mantle must encounter both a stress field that favors a radial dike configuration and something that redirects ascending magma laterally at shallow depths within the lithosphere. The former condition is straightforward to create via large-scale flexural uplift in response to plume impingement, underplating, or a similar mechanism; however, the stress state resulting from this process strongly favors continued ascent and eruption, inconsistent with evidence of long-distance lateral transport of magma through the radial dikes.

In a paper recently published in the journal Icarus, Dr. Gerald Galgana, Dr. Patrick McGovern (colleagues from the Lunar and Planetary Institute in Houston, TX) and I have demonstrated that initial eruptions related to flexural uplift can produce a surface load (e.g., a large volcanic edifice) that acts to counter the uplift, suppressing upward flexure and simultaneously creating a stress cap of sufficient magnitude that lateral redirection of magma into radial dike systems becomes likely. This exciting new understanding links mechanical processes acting upon the lithosphere directly to the volcanological outcomes, improving our insight into the formation and evolution of some of the largest magmatic systems and radial dike swarms identified on multiple planets.

For more information: Galgana, G.A., E.B. Grosfils and P.J. McGovern, 2013. Radial dike formation on Venus: Insights from models of uplift, flexure and magmatism. Icarus, 225, 538-547.

I’ve often been asked, as a faculty member at a small liberal arts college — a setting traditionally and fiercely dedicated to the pursuit of excellence in teaching — why I want to perform research. Sure it’s intellectually delightful to explore and to challenge myself to advance what we know about a research subject in which I’m interested, like physical volcanology or planetary science, but it takes a seemingly never-ending stream of energy to write successful grants, pursue questions that don’t always yield fruitful outcomes, publish the results obtained when something new is learned, etc. Wouldn’t that time and energy be better spent honing my skills as a teacher? An answer to this is articulated succinctly in a quote that comes from a 1-page article (on pg. 47 of course!) in the Summer 2013 Alumni Magazine published by my undergraduate alma mater, the College of William and Mary:

“What is discovered in research one day is taught in the classroom the next, and then employed as a tool of economic development, innovation and, in some cases, national defense. The false notion that teaching in universities serves students but that research in universities does not betrays a profound misunderstanding of how academic institutions become great — and stay great.” — R.M. Gates, W&M ’65

There are clearly connections to teaching when I involve and mentor students, but it is important to recognize as well that my teaching and capabilities as an instructor usually benefit even when no students are directly involved in the research I perform. As a liberal arts instructor then my answer to the question I’m often asked is simple: I believe that doing research makes me a better teacher.

In my view, striving to become a more effective teacher is a goal which more than justifies the time and energy required to perform scholarly research, and I am grateful for the opportunities I have had in this arena. Of course, the fact that I also derive deep satisfaction from gaining new insights with the potential to help people directly, or that simply increase our knowledge in a more abstract way about the fascinating solar system in which we reside, is simply icing on the proverbial cake!

Addendum (7/27/13): In its 2013 list of top colleges in the US, Forbes ranked Pomona College #2 nationally. While ranking results like this should always be taken with a big grain of salt, I think it likely that the incredible dynamicism of my teacher-scholar colleagues plays a central role in our continued success where such evaluations are concerned…

One of the best parts of my job as a faculty member is the opportunity I have to perform research with talented students. The group above, which came together to perform a numerical modeling project in the summer of 2011, is a great example… and it has been almost as much fun following their subsequent activities. I reported previously on Ben Murphy ’13 (back, second from right), who won a 2012 Goldwater Scholarship, and I’m very proud to report that Kyle Metcalf ’14 (front, left) now joins him as a 2013 Goldwater recipient. In addition, I am delighted to report that Lorelei Curtin ’13 (back, middle) has been selected as a Fulbright Graduate Scholar, and in that role she will begin research on the lovely South Island of New Zealand next year. My heartfelt congratulations go out to Kyle and Lorelei!

Each student carves their own path forward, and nothing makes me happier than to see individuals tap into their strengths as they pursue their own interests. Shelley Chestler ’12 (front, middle), for example, is now part of the strong graduate program at the University of Washington, where she continues to pursue her interests in quantitative geoscience. Following a very different but equally challenging path, Julita Penido ’12 of Mt. Holyoke (back, second from left) has chosen to pursue her interests in film and theater here in southern California (I can’t help but imagine how great it would be to have an actual scientist playing the lead role in some future geology-themed blockbuster!). Rounding out the group, Gustavo Ruiz ’13 (back, right) and James Muller ’13 (front, right) are still enmeshed in their senior year responsibilities, but as they prepare to make their own leaps forward I am eager to see what these two engaging fellows choose to do next!

— pit crater chain in Iceland (from Fig 3 of Ferrill et al., 2011)

In a 2013 Canadian Journal Of Earth Sciences paper published in a Special Issue recognizing “Canadian contributions to planetary science,” colleagues Sarah Davey, Richard Ernst, Claire Samson (all at Carleton University) and I present an analysis of factors that contribute to pit crater chain formation in several areas of Venus — including the Ganiki Planitia (V-14) quadrangle region mapped previously with the aid of Pomona College students and colleagues (Grosfils et al., 2011). We compare pit crater chain morphologies and clustering characteristics with mapped structures and geomorphological units, and propose that pit craters form above extensional graben covered with friable, possibly volcaniclastic material. While this hypothesis requires further testing via mapping in other areas, our results are quite exciting because it is difficult to detect volcaniclastic materials on Venus using only Magellan radar data. If the proposed link between the presence of such materials and an easily recognizable morphological feature seen in radar data can be confirmed, it would yield a powerful new tool for advancing our understanding of Venusian volcanism and contribute to our general understanding of pit crater chains — an enigmatic volcanic feature observed on numerous planets and moons in the inner and outer solar system.

For more information: Hierarchical clustering of pit chains on Venus

In late September I travelled ~100 km north of Rome to the medieval village of Bolsena, on the shores of the Bolsena caldera-filling lake (see photo below), to attend the 4th International Commission on Collapse Calderas workshop sponsored by IAVCEI. Focused on part of the Vulsini Volcanic District, this was one of the most stimulating professional exchanges I’ve had in quite some time, bringing together scientists from all over the world with expertise ranging from analogue and numerical modeling to petrology, geochemistry and field mapping.

After two days of talks (including my presentation and one by collaborator Trish Gregg of Oregon State University) and general discussion about the state-of-the-art where our understanding of caldera formation is concerned, the ~40 attendees spent three days in the field studying the morphology, structures and deposits of the spectacular Bolsena, Latera and Vico calderas. For me, these days in the field not only provided a chance to understand physical constraints important for my modeling, and the chance in turn to inform field interpretations using my numerical data, but they also gave me the opportunity to meet some terrific caldera-focused volcanologists from all over the world — who turn out to be a particularly nice collection of people!

On the first day we were introduced to the characteristic expressions of the Bolsena caldera. The typical products of an explosive eruption like this are shown at left, in this case derived from the ~295 ka Orvieto-Bagnoregio caldera-forming eruption associated with a major stage of Bolsena’s collapse. At the base is a plinian fall deposit, rich in pumice with a popcorn-like appearance. Immediately above this is a sharp contact marking the base of a coarsening-upward ignimbrite, the product of a pyroclastic flow.

Subsequent to the collapse of the main caldera, incremental subsidence of Bolsena continued. This deformation is reflected in an unusual and remarkably well exposed sequence of extensional faults that helps define the modern structural expression of the caldera. The image below, for instance, shows a complex sequence of normal and reverse faults located within a large extensional graben that is exposed here in an outcrop aligned radial to the caldera rim.

This part of Italy is truly lovely, and much of the spectacular scenery owes its beauty at least in part to the explosive deposits we were there to examine. For instance, many of the hilltop villages like Bagnoregio, shown at right, were constructed centuries ago on isolated mesa-like peaks carved from materials deposited by caldera-sourced eruptions — in this case a thick sequence of the Orvieto-Bagnoregio ignimbrite. As we explored the volcanic terrain, we were thus treated to a cultural and scenic feast — Etruscan, Roman and Italian — that certainly had me enjoying the many ways this field locale is so wonderful!

On the second and third days we explored the Latera and Vico calderas; a view of Vico Lake seen from our lunch stop, with Monte Venere on the far side, is shown below. Like Bolsena, these calderas are very well exposed, and they provide an introduction to a wide array of deposits associated with caldera-forming eruptions. For example, I saw: fantastic accretionary lapilli, thought to form in a matter crudely analogous to the way hailstones grow in a storm cell; lag breccias, used to infer eruptive vent locations; sequences indicative of energy variations that occur during phreatomagmatic eruptions; and, a stunning deposit of delicate, meter-scale spatter located miles from the nearest known vent.

While my conversations with the workshop attendees taught me a great deal concerning what has been learned about caldera-forming events in the Vulsini Volcanic District, a critical component of our exchanges involved searching for the edges of what is known, and thereby defining the areas where more research is needed. This was the first CoCC workshop I have attended, but I certainly look forward to the chance to attend the next meeting in New Zealand two years from now, and it will be interesting to see what new advances occur between now and then!

In a 2012 Journal of Volcanology and Geothermal Research paper, colleagues Patricia Gregg, Shan de Silva, John Parmigiani (all at Oregon State University) and I present our analysis of the volcanic conditions needed to form a large caldera (e.g., Long Valley, CA). Supereruptions associated with large caldera growth have caused regional- to global-scale devastation regularly throughout Earth’s recent geologic history, and improving our understanding of how such events occur is thus of obvious societal concern.

Utilizing new temperature-dependent, viscoelastic finite element models that incorporate a Mohr-Coulomb failure criterion, we show that eruptive failure of the largest magma chambers is a function of the geometry of the overlying roof and the location of the brittle-ductile transition. As magma pressure increases within a candidate magma chamber, extensive uplift of the overlying roof promotes fault propagation that can trigger caldera subsidence and lead to supereruption. Our thermomechanical models also provide an estimate of the maximum size of magma chamber growth in a pristine host material and, thereby, an estimate of the maximum size of the resultant caldera.

For more information: Catastrophic caldera-forming eruptions: Thermomechanics and implications for eruption triggering and maximum caldera dimensions on Earth

Students: Want to get involved in caldera research?

— Sketch illustrating thermomechanical models of caldera and eruption initiation (Gregg et al., 2012)

Students:

I have recently received two grants from NASA to commence research into

1. the three-dimensional mechanics of caldera formation; and
2. the formation and time-dependent evolution of large volcanoes.

If you would like to help advance our knowledge of these two fundamental physical volcanology processes while developing new skills in numerical modeling, GIS mapping and/or planetary remote sensing image analysis, please contact me at any time to discuss the planned research and how you might contribute in more detail. There will be funded opportunities for at least two undergraduate students to participate for eight weeks during each of the next three summers (2013-2015).

NASA’s Planetary Geology & Geophysics program has just announced the group of 2011 proposal submissions selected for funding. I’m excited to report that both of the proposed research projects with which I am involved received full support. A brief description of each project is provided below, and there are multiple opportunities for student involvement. 

Three-dimensional Analysis of Ring Fault Initiation and Caldera Formation on the Terrestrial Planets (Grosfils, PI)

The geological records preserved on Earth, Venus and Mars clearly illustrate the considerable extent and magnitude of the devastation that can accompany caldera formation and associated eruption events. There is thus obvious scientific and societal motivation to improve our understanding of the processes that precipitate, and are associated with, caldera formation. Since calderas often form in tectonically complex environments, our goal is to develop, test and apply fully three-dimensional models that can be used to gain insight into ring fault initiation and caldera formation in such settings. (This project advances research begun when I was a Fulbright U.S. Senior Scholar at the University of Auckland, and complements related efforts ongoing with colleagues in OR and TX.)

Growth and evolution of large volcanoes on Venus: Insights from advanced numerical modeling of lithospheric response to volcanic loading (Grosfils, Co-I)

The volcanoes of the planet Venus display a diverse range of sizes, shapes, lava flow distributions, and tectonic signatures, and our goal is to decipher what these data can tell us about the growth and evolution of large volcanoes. To date we have used static elastic models to explore how edifice-induced lithospheric flexure affects the mechanics of magma reservoir failure and magma ascent. By introducing a viscoelastic rheology, in the next stage of our research we seek to understand the time-dependent evolution of the conditions that promote large edifice construction. (This project builds upon results from six years of PG&G funded research (McGovern, PI), and takes the next logical step by moving our research from elastic to inelastic conditions.)

-- model of magma reservoir and plume beneath Mbokomu Mons, Venus (Credit: Dr. Gerald Galgana, LPI)