Archive for the ‘Research’ Category

— Visiting Many Volcanoes in 2017-2018

May 14th, 2018

My research is predominantly organized around numerical modeling of subsurface volcanic processes. I would never claim to be a field geologist, but even so my insight into volcanic processes is enhanced every time I have a chance to observe volcanic phenomena and products directly. Happily, this past year I have enjoyed ample opportunities to visit several different volcanoes–on my own, with colleagues, and with students.

Morro Rock, CA (Mar., 2017): During a trip up the California coast I visited Morro Rock. The iconic 575′ volcanic plug is the westernmost of an aligned series of intrusives that formed ~22 million years ago. Originally located deep underground, this dacitic plug is probably the remains of a volcanic conduit system. Today it anchors the Morro Bay harbor, and is a stunning landmark along this stretch of the California coast.

Morro Rock dacitic plug at sunset

Kilauea/Mauna Loa/Hualalei, HI (May, 2017): Before and after the Cordilleran GSA meeting in Honolulu I had a chance to spend a number of days on the Big Island of Hawaii.

Several of these days were spent on a GSA field trip run by Dr. Tina Neal and Dr. Don Swanson, current and former Scientists in Charge at the Hawaii Volcano Observatory. On this engaging and informative trip we were introduced to a number of stunning volcanic landscapes and processes–one of my favorites was a superelevated lava flow emplaced in 1974–but our primary focus was to examine several summit deposits and processes on Kilauea, including those associated with the infamous 1790 explosive sequence.

Super elevated flow channel (banked flow seen at left) with gas from Overlook Crater, Kilauea caldera, in the background

After GSA, where I presented an analysis of caldera formation on Mars, I returned to the Big Island for some less formal exploration, generously guided by my friend and Emeritus Professor of Geology (retired) Rick Hazlett, who now lives in Hilo. One of my dreams for the Volcanology course I teach at Pomona is to secure enough funding to support an every-other-year trip to Hawaii for the enrolled students; this would enable them to apply their quantitative skills to field-based problems in this volcanic wonderland, and would also enrich the course with several key qualitative analyses. With that goal in mind, Rick and I explored an array of sites on Kilauea, Mauna Loa and Hualalei to assess their suitability. We walked through lava tubes, looked at channelized flow processes and tree molds, enjoyed coastal exposures, did a detailed walk-through of Kilauea Iki, and visited a large number of lava-structure interactions to gain insight into this pervasive element of the Hawaiian experience.

Mantle xenoliths in a flow on the Big Island

Mt. Hood, OR (Aug., 2017): Toward the end of the summer I attended the IAVCEI Scientific Conference in Portland, where I presented a “where are we now” talk sharing new insights into the mechanics of radial dike formation at several different scales. One day of the conference was dedicated to field trips, and I had the good fortune to see a volcano I’d never visited: the iconic Mt. Hood. The lovely composite cone geometry is a product of lava effusions and repeated lava dome collapses that fed pyroclastic flows, and it has experienced vigorous lahar activity as well.

Lamar deposits from Mt Hood, OR

Mt. St. Helens, WA (Aug., 2017): After the IAVCEI conference my family flew up to Oregon to watch the solar eclipse (the zone of totality passed just south of Portland; it was incredible!), and we took the opportunity to visit Mt. St. Helens. This trip was a “tourist” visit, not a professional one per se, but I took a lot of photos to use in my volcanology course and really enjoyed the chance to see the products of the volcanic avalanche (I visited the much larger deposits around Mt. Shasta in California a few years back), the current dome growing in the crater, and the trees that had been knocked flat by the blast. Roughly a third of a century later the region has recovered to some extent, but the signature of the May 1981 eruption still dominates the landscape quite clearly.

Mt St Helens volcano, WA

Amboy Crater, CA (Feb., 2018): After studying lava flows for a bit, my volcanology class took a trip out to see the Amboy Crater scoria cone in the Mojave Desert. I have been visiting this site for many years, but see something new every time I’m there. This year, in addition to studying the sequence of events that formed the cone and surrounding lava flows, we took some first-order measurements of tumuli to try and assess the magma pressure responsible for their inflation. It’s nice having such a pristine volcano only a few hours away from campus!

BPVF/Long Valley/Panum Crater, CA (Apr., 2018): Toward the end of the spring semester the volcanology and petrology classes took a joint, multi-day field trip to see parts of Owen’s Valley, Long Valley and the Mono Basin, which together exhibit a breathtaking array of volcanic styles.

Owens Valley, Long Valley and Mono Basin field area.

Several of our stops occurred in the Big Pine Volcanic Field (BPVF), where we examined S-type granites and Independence dikes at Kern Knob, the faulted Fish Springs cone, and the incredible Papoose Canyon cone which has been neatly bisected by a fluvial channel, thereby providing hands-on access to the majority of the xenolith-rich flow sequence that built the cone.

Entrance to Papoose Canyon.

Papoose Canyon xenolith and contact.

At Long Valley we spent considerable time studying deposits emplaced during the cataclysmic caldera-forming Bishop Tuff eruption that occurred 767 thousand years ago. This ‘supereruption’ emplaced ~600 km^3 of felsic material over a few short days as the ring faults ‘unzipped.’ Much of our time was spent examining the airfall and ignimbrite exposures at the classic Chalfant quarry site, but we also visited several other locales to examine variations in the degree of ignimbrite welding and to view the southern part of the caldera and resurgent dome from afar!

Bishop Tuff airfall and ignimbrite, Chalfant Quarry

Finally, not content with basaltic cones and massive ignimbrite eruption deposits, we visited Panum Crater, the northernmost member of the Mono Domes and, having formed only 600 yrs ago, the youngest. Although it has enjoyed a complex history, Panum today is defined by a cavity formed during an early phreatomagmatic explosion, a low tuff ring formed during an intermediate Strombolian eruption, and a terminal, conduit-plugging silicic dome that exhibits obsidian banding, bread crust textures, and debris from collapsed spines. Yielding stunning views across the Sierran front and the Mono Basin (including the Paoha, Negit and Black Point constructs — parts of the volcanic story that will have to wait for a different trip!), Panum was a great way to end the middle day of our field trip!

Lovely fracturing in obsidian atop Panum Crater’s silicic dome

Mono Lake (left), Mono Domes (right skyline), Panum crater tuff ring (foreground, curving to the right) and silicic dome (casting shadow)

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— 3-Year NASA SSW Grant Awarded

May 2nd, 2018

Exploring exciting new research questions with my students and colleagues is one of the most fun parts of my job, but many of these pursuits require funding–and chasing that down isn’t quite as much fun. Grant proposals take a long time and a lot of effort to prepare, and the odds of landing a grant are low, roughly on par with what it takes to be admitted as a student at Pomona College right now. So, when a grant is ‘landed’ it is a cause for celebration!

I’m therefore pleased to report that a proposal I submitted recently to NASA’s Solar System Workings program with my Lunar and Planetary Institute colleague Dr. Pat McGovern (PI), was among those selected for funding. Entitled “Breaking the barriers: Time-dependent, stress-controlled growth of large volcanoes on Venus and implications for the mechanics of magma ascent, storage, and emplacement,” the funds from this grant will allow several students to contribute to GIS- and/or numerical modeling-grounded research during the summers of 2018-2020. I’m excited to get underway with the first students in a few short weeks!

For more detail, a Pomona College press release about the grant can be found here.

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— Origin of Polygonal Ridge Networks on Mars

February 17th, 2017

Research conducted during the past two decades, which some might describe as the “golden age” of Mars-directed planetary exploration, has taught us a tremendous amount concerning the formation and evolution of the red planet. At the same time, however, scientists’ observations have raised many new questions, and as we continue to explore we learn more every day about exciting new areas such as Mars’ ice ages and climate variations, the role of water, the timing of volcanism, the rate of impact cratering, and many other processes.

Recently, in a study that connects observations ranging in time from the Viking missions in the 1970’s right up to the present, I worked with colleagues from JPL (Laura Kerber, PO ’06) and Brown University (including my former Ph.D. advisor Jim Head) to investigate the formation of unusual polygonal ridge networks on Mars (Figure 1). How do these ridge networks form and what insights, especially into groundwater circulation on Mars, might they therefore provide?

As is often true, the answer is complex: several different mechanisms seem to operate, though all share in common an origin linked to fractures that were later infilled by materials more erosion-resistant than their surroundings. Based on their geologic setting, their spatial correlation (or not) with other chemical and/or hydrological signatures, and their weathering behavior, many polygonal networks appear to have originated as fractures infilled by hydrous mineral deposits, while other networks are more likely fracture systems infilled by magma and/or lava in the near-surface environment. Still other networks may have been infilled by sediments that were later preferentially cemented, rendering them more resistant to regional erosion, but the origin of this feature class remains somewhat enigmatic based on observations available to date.

A great deal remains to be learned, and our initial study makes it clear that as more high resolution data become available new polygonal ridge network examples will continue to be identified, expanding our understanding of these intriguing geologic features. Indeed, as of early 2017 citizen-science volunteers are encouraged to get involved in the search for new examples, with results potentially being used to direct future observations by the HiRISE camera and similar instruments currently in orbit around Mars (see below)!

Figure 1: A HiRISE color close-up of a polygonal ridge network in Gordii Dorsum, Mars (ESP_045409_1915).

For more information:


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— Magma Buoyancy and Reservoir Rupture

November 8th, 2015

Magma accumulating in a shallow subsurface reservoir tends to have a lower density than the crustal rocks within which the reservoir is embedded. Intuitively, then, buoyant stresses derived from this rock-magma density difference should contribute to how a reservoir evolves, and many volcanologists argue that magma buoyancy is a critical driver of magma reservoir rupture that leads to eruption. Quite recently, two increasingly cited 2014 papers published in Nature Geoscience continued this trend by contending that rock-magma density differences in fact produce sufficient buoyancy to destabilize a massive magma reservoir, leading directly to rupture that can yield a supereruption.

Magma buoyancy, of course, is just one of many stresses that will interact to dictate the stability of a magma reservoir, and it is important to examine these stress interactions carefully when characterizing reservoir rupture and the possibility that an eruption will occur. In a 2007 paper published in the Journal of Volcanology and Geothermal Research, for example, I used elastic finite element models to show that rock-magma density differences, relative to the other factors involved, play almost no role in the rupture of a small magma reservoir, i.e. one typical of what is found beneath a shield or composite volcano (Figure 1).

Fig 1: For host rock of density 2600 kg/m^3, demonstration that rupture location (small arrows) is invariant for magma densities ranging from 1000-3400 kg/m^3 [for full details, see Figure 6 in Grosfils (2007)]

Fig 1: For host rock of density 2600 kg/m^3, rupture location (at small arrow locations in (a), at depth h=0 for all cases in (b)) is invariant for magma densities ranging from 1000-3400 kg/m^3 [for full details, see Figure 6 in Grosfils (2007)].

More recently, via a 2015 paper just published by the Journal of Volcanology and Geothermal Research, colleagues Patricia Gregg (University of Illinois Urbana Champaign), Shan de Silva (Oregon State University) and I expand upon this earlier analysis of magma buoyancy to assess the role buoyancy plays in larger, supereruption-sized systems. In addition to challenging the validity of the quantitative methods employed in the two 2014 Nature Geoscience papers, we use time- and temperature-dependent viscoelastic finite element models to demonstrate that, for immense magma reservoirs, rock-magma density differences–even when carried to an extreme–are insufficient to destabilize the system, induce rupture, or trigger an eruption (Figure 2).

Fig 2: when buoyancy is treated without correctly integrating it into the complex suite of stresses in the host-reservoir system, significant deformation and faulting is predicted (a), but modeling buoyant stresses as an integral part of the system reveals that it has minimal impact (b). [For full details, see Figure 5 of Gregg et al. (2015)]

Fig 2: When buoyancy is treated without correctly integrating it into the complex suite of stresses in the host-reservoir system, significant deformation and faulting is predicted (a), but modeling buoyant stresses as an integral part of the system reveals that it has minimal impact (b) [for full details, see Figure 5 of Gregg et al. (2015)].

This outcome is consistent with previously articulated characteristics of large caldera-forming eruptions, and after eliminating buoyancy as a critical factor we continue to argue, as articulated by Gregg et al. (2012), that external triggering assisted by other reservoir-internal factors (Figure 3) is currently the most plausible model for the conditions that lead to rupture of the massive magma reservoirs capable of feeding some of the largest, most devastating eruptions on Earth.

Fig 3: Viscoelastic model for incremental reservoir pressurization and fault evolution of a supereruption-sized magma reservoir system. [See Figure 10 of Gregg et al. (2012) for full details]

Fig 3: Cartoon of viscoelastic model results depicting incremental reservoir pressurization and fault evolution for a supereruption-sized magma reservoir system [for more details see Figure 10 of Gregg et al. (2012)].

For more information see:

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— Lithosphere Layering Aids Radial Diking

August 20th, 2015

As described in a previous post, giant radial dike systems may be commonly observed on Earth and Venus but that doesn’t mean they’re easy to form! In a paper recently published in the Journal of Geophysical Research-Planets, Dr. Nicolas Le Corvec, Dr. Gerald Galgana, Dr. Patrick McGovern (colleagues from the Lunar and Planetary Institute in Houston, TX) and I show that mechanical layering — i.e. including crust and mantle layers explicitly within a modeled lithosphere — can help promote radial dike formation and long-distance propagation. Specifically, when a mechanically layered lithosphere flexes due to either surface or basal loading (e.g., in response to edifice growth or plume impingement), radial dikes formed by rupture of an inflating magma reservoir can in some circumstances  propagate for 100’s of kilometers. In addition to providing new mechanical insight into giant radial dike swarm formation, our results are also important because the lateral extent of giant radial dike systems can, in theory, provide a new way to constrain the ratio of crust and mantle lithospheric layer thicknesses on Venus.

For more information: Le Corvec, N., P.J. McGovern, E.B. Grosfils, and G. Galgana, 2015. Effects of crustal-scale mechanical layering on magma chamber failure and magma propagation within the Venusian lithosphere. Journal of Geophysical Research-Planets, 120, doi:10.1002/2015JE004814.

Le Corvec Fig

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— Goldman (PO ’15) Receives Fulbright Award

August 20th, 2015
Robby commences his Fulbright by mapping volcanic units at Ngauruhoe volcano, New Zealand

Robby commences his Fulbright by mapping volcanic units at Ngauruhoe volcano, New Zealand

Robby Goldman (PO ’15), who spent his summer and senior year using finite element models to explore caldera formation, was recently chosen to receive a Fulbright Award that enables him to spend 2016 in New Zealand continuing his research under the guidance of Darren Gravley (’96). In 2017 Robby will expand his skills as a graduate student working with Trish Gregg at the University of Illinois Urbana-Champaign. My heartiest congratulations Robby!

More information:

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— Terrific Caldera Conference in Taupo, NZ

August 20th, 2015

In December of 2014 I attended my second IAVCEI sponsored conference focused on collapse calderas. Happily, the conference took place in and around Lake Taupo within the Taupo Volcanic Zone on the north island of New Zealand, site of one of the youngest known “supereruptions” on Earth. With two days of conference presentations and discussion, bracketed by field days spent exploring the Taupo and Rotorua calderas and other local volcanics, the conference was a great opportunity to continue advancing our understanding of the chemical signatures, mechanical processes and field deposits that characterize large caldera formation.

-- Rotorua Caldera

— Rotorua Caldera

After the conference I treated myself to a Lord of the Rings day, albeit one that continued to explore a strongly volcanic theme! Driving north from Taupo I first visited the Hobbiton movie set, located within scenic ignimbrite deposits.

-- hobbit holes

— hobbit holes

-- Hobbiton's view of the Green Dragon inn

— Hobbiton’s view of the Green Dragon inn

After enjoying Hobbiton I drove south past Lake Taupo to have a quick look at Mt. Doom (Ngauruhoe) and two adjacent volcanoes (Ruapehu, Tongariro) within Tongariro National Park. I didn’t have enough time for a tramp, but will look forward to that on my next visit!

-- Lovely but dangerous Mt. Ruapehu

— Lovely but dangerous Mt. Ruapehu

With conferences in Bolsena, Italy and now in Taupo, New Zealand setting a high standard, I look forward very much to the next IAVCEI caldera conference, which will be held in Hokkaido, Japan in the Fall of 2016!

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— Solar System Volcanism and Tectonism

January 9th, 2015

Bringing together several years of research with students and colleagues, I recently published two papers in the book “Volcanism and Tectonism Across the Solar System,” Geological Society of London Special Publication 401, which is due for release in 2015. The first paper, entitled Elastic models of magma reservoir mechanics: a key tool for investigating planetary volcanism, uses elastic finite element models to demonstrate how the interplay between volcanic elements – such as magma reservoir geometry, host rock environment (with an emphasis on understanding how host rock pore pressure assumptions affect model predictions), mechanical layering, and edifice loading with and without flexure – dictates the overpressure required for rupture, the location and orientation of initial fracturing and intrusion, and the associated surface uplift. The second paper, entitled Lithospheric flexure and volcano basal boundary conditions: keys to the structural evolution of large volcanic edifices on the terrestrial planets, examines how flexure of the mechanically strong outer layer of a planet influences magma ascent paths and chamber dynamics in the lithosphere, often favoring the development of oblate magma chambers or sill complexes.

For more information see:

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— Students Present Research at 2014 LPSC

September 22nd, 2014

This past March, two current students and one recent graduates culminated their research with Prof. Grosfils by giving a presentation at the 2014 Lunar and Planetary Science Conference in Houston, TX. Weighing in at his first conference, Jack Albright (’16) represented the rest of the student and faculty team (John Baxter ’09, Peter Ferrin ’14, Dr. Grosfils, Dr. McGovern) as he explained the team’s new insights into “Using Mapping-derived Quantitative Strain Estimates to Test Uplift versus Dike Emplacement Models for Giant Radial Lineament System Formation on Venus” to a diverse array of planetary scientists. Continuing our tradition of celebrating student achievement and performance at the conference, the presenters joined other Sagehen alumni attending the conference for some conversation and reminiscing over refreshments: as always, it is terrific to see current and former students mixing it up and sharing stories about their Sagehen days!


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— Chestler (’12) Publishes Galapagos Thesis

October 1st, 2013

FernandinaI am pleased to report that Shelley Chestler (’12) and I have just published her senior thesis research in the journal Geophysical Research Letters. Using numerical finite element models, and targeting Fernandina volcano (shown at right) as a case study, the article demonstrates how minor, volcanologically plausible variations in a magma reservoir system can lead to the intrusion of radial, circumferential, and corkscrew-style dikes akin to those that characterize many volcanoes in the Galapagos and elsewhere. This result is an exciting one, offering a solution to a problem that has puzzled geologists for some time, and complementing other recent edifice-modeling efforts (e.g. Hurwitz et al. 2009; Galgana et al., 2012) we have now identified conditions that can lead directly to lateral intrusion of radial dikes from a shallow magma reservoir.

For more information: Chestler*, S.R., and E.B. Grosfils, Using numerical modeling to explore the origin of intrusion patterns on Fernandina volcano, Galapagos Islands, Ecuador, Geophysical Research Letters40, 4565-4569, doi:10.1002/grl.50833, 2013.

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