Understanding Monsoons

Studies of the global environment are complex, involving interactions between oceans, solid earth, biological systems, and the atmosphere, over time scales ranging from nanoseconds to millions of years. Investigating and understanding these complicated and interconnected systems is the goal of Caltech's Ronald and Maxine Linde Center for Global Environmental Science. To that end, the center hosts workshops that bring together scientists from a range of disciplines to discuss current research and collaborate on solutions to pressing issues facing the global environment.

"The Linde Center workshops aim to provide a venue for a small group of scientists and engineers to discuss and put forward cutting edge, 'future-looking' plans for global environmental science," says Paul Wennberg, the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering and director of the Linde Center.

The topic of the center's latest workshop, held May 18–22, was monsoons, circulation patterns that develop over subtropical continents (up to around latitude 30 degree north and south of the equator) in response to seasonal variations in the amount of solar radiation received in these regions. Monsoons are characterized by seasonally reversing winds and summertime rainfall. Although monsoons occur across the globe, they are more often studied in Southeast Asian countries—where warm, moist air from the Indian Ocean brings humidity and rainfall during the summer, while winds from the northeast produce dry winters—and in West Africa. Because of their effects on the water supply, monsoons have a large impact on society, especially in densely populated countries and rapidly growing economies. And, as noted by the workshop organizers, "with projected increases in population and pressure for food and water security, understanding how anthropogenic climate change will affect monsoons is both a priority and a major challenge in climate science."

Indeed, the workshop—entitled "Monsoons: Past, Present, and Future" and co-led by monsoon researcher Simona Bordoni, assistant professor of environmental science and engineering at Caltech—was focused on understanding how monsoons have changed and how they will change in the future, across a variety of time scales, in response to different forcing agents—perturbations of Earth's energy balance caused by changing environmental parameters such as solar variability or human-induced greenhouse gas emissions.

"One of the central themes of the discussion," Bordoni says, "was how modern theories of the fundamental dynamics of monsoons can be used to better constrain future monsoon projections and past monsoon changes and shifts recorded by paleo-proxies"—media such as tree rings and ice cores that preserve information about past climates—"and how these paleo-reconstructions can provide support to emerging hypotheses and guide modeling studies. The implications of these modern theories are only now beginning to be explored."

Each section of the invitation-only workshop covered a particular subject area within monsoon research, including paleoclimate, aerosols, the intertropical convergence zone (the band of clouds encircling the equator), and thermal contrasts between land and sea. Speakers from institutions around the country gave talks on past and potential future changes in the monsoon cycle, the role of aerosols on monsoon circulation, and monsoon modeling, among other topics.

In a talk entitled "Monsoons on Idealized Continents," for example, Bordoni discussed how she uses models of "idealized" continental geometry to study how monsoons would develop on hypothetical planets—for example, a planet with land everywhere above 10 degrees north of the equator, and ocean everywhere south of that. Recently, Bordoni and her group also created simulations of an "aquaplanet"—a planet entirely covered with ocean. With the aquaplanet simulations, the team demonstrated that the rapid onset of large-scale monsoons, such as the Asian monsoon, results not from temperature differences between oceans and land, as previously believed. Instead, they found, the rapid appearance of this monsoon is controlled by the interaction between large swirling regions of turbulent air called eddies and the tropical circulation. These eddies, which are generated in mid-latitudes, propagate to lower latitudes towards the subtropics and interact with the tropical circulation, causing it to reverse rapidly, initiating the onset of the monsoon. Bordoni's group also studies the North American monsoon, which usually occurs during the summer over southwestern North America, when warm and moist air moving northwest from the Gulf of California meets similar air moving northwest from the Gulf of Mexico; the dynamics of the East Asian monsoon and its response to climate changes; the year-to-year variability of the Indian monsoon; and how mountain ranges such as those in Africa and Asia influence the larger-scale circulation of this monsoon.

The workshop was co-led by Timothy Merlis (Ph.D. '11), an assistant professor in atmospheric and oceanic sciences at McGill University. He gave a talk on tropical circulation changes influenced by various forcing agents. Other speakers from Caltech included Jess Adkins, professor of geochemistry and global environmental science, who gave a talk on historical precipitation variability over Borneo as measured in stalagmites; Salvatore Pascale, a NOAA Climate and Global Change postdoctoral scholar in environmental science and engineering; and Ho Hsuan Wei, a graduate student in environmental science and engineering. Hui Su, a JPL atmospheric scientist, gave a talk on the tropical Hadley cell (a pattern of atmospheric circulation in which warm air rises near the equator, cools as it travels at high altitude toward the poles, then sinks as cold air and warms as it travels toward the equator) and feedback from clouds. In addition, JPL scientist Christian Frankenberg—who will join the Caltech faculty in September as an associate professor of environmental science and engineering—discussed remote sensing of water isotopes.

The previous Linde Center workshop was held February 2–5 and focused on physical, chemical, and biological processes crucial to the circulation and ecosystems of the Southern Ocean around Antarctica.

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Thursday, September 24, 2015
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2015 Teaching Conference - Save-the-Date

New Dean of Graduate Studies Named

On July 1, 2015, Doug Rees, the Roscoe Gilkey Dickinson Professor of Chemistry, will begin serving as the new dean of graduate studies at Caltech.

"Doug's experience and concern with graduate education make him an ideal choice for dean of graduate studies. I am very pleased that he is willing to make this commitment to the Institute and its students," says Anneila Sargent, vice president for student affairs and the Ira S. Bowen Professor of Astronomy.

As the new dean, Rees will be the principal administrator and representative of Caltech's graduate education program, responsible for attending to concerns regarding the welfare of graduate students as well as for upholding the Institute's rules and policies.

"There are many groups essential to the effective operation of our graduate program that I want to get to know better, starting with the graduate students, the Graduate Office staff, and the option administrators and option reps," says Rees. "In my 26 years at Caltech, I've gained an appreciation for how the graduate programs in biochemistry and molecular biophysics and in chemistry operate, but the cultures in different options across campus can vary significantly, and I look forward to better understanding these distinctions."

Rees says that he is also very much looking forward to working directly with graduate students, staff, and faculty on behalf of the graduate program. Of particular interest during his tenure will be issues relating to the well-being and professional development of graduate students.

"I find research to be an adventure that, while exhilarating, is also challenging, frustrating, and even stressful; those aspects, however, are not incompatible with having a positive student experience and a supportive environment," Rees says. He adds that his priorities will be to raise fellowship support, increase the diversity of the graduate student body, and ensure that students have access to appropriate support services such as health care, counseling, and day care. "In addition, I also hope to be able to explore mechanisms to better prepare students for life after Caltech, including both academic and nonacademic career options," he says.

In his new post, Rees will take the place of C. L. "Kelly" Johnson Professor of Aeronautics and Mechanical Engineering Joseph Shepherd, who has served as the dean of graduate studies since 2009. "Joe leaves big shoes to fill and the campus owes him a huge debt of gratitude for all he has accomplished as dean of graduate studies. What I have learned from watching him in action over the past six years, and more recently as he has been helping me during this transition period, is that the most important quality for the dean is to care about the students—and I will definitely be working to follow his example," Rees says.

Rees received his undergraduate degree from Yale University in 1974 and his PhD from Harvard in 1980, becoming a professor at Caltech in 1989. An investigator with the Howard Hughes Medical Institute, Rees also served as the executive officer for chemistry from 2002 to 2006 and the executive officer for biochemistry and molecular biophysics from 2007 to 2015.

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JPL News: NASA Joins North Sea Oil Cleanup Training Exercise

NASA participated for the first time in Norway's annual oil spill cleanup exercise in the North Sea on June 8 through 11. Scientists flew a specialized NASA airborne instrument called the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) on NASA's C-20A piloted research aircraft to monitor a controlled release of oil into the sea, testing the radar's ability to distinguish between more and less damaging types of oil slicks.

Read the full story from JPL News

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Caltech, JPL Team Up to Take On Big-Data Projects

Acknowledging not only the growing need among scientists and engineers for resources that can help them handle, explore, and analyze big data, but also the complementary strengths of Caltech's Center for Data-Driven Discovery (CD3) and JPL's Center for Data Science and Technology (CDST), the two centers have formally joined forces, creating the Joint Initiative on Data Science and Technology.

A kickoff event for the collaboration was held at the end of April at Caltech's Cahill Center for Astronomy and Astrophysics.

"This is a wonderful example of a deep cooperation between Caltech and JPL that we think will serve to strengthen connections between the campus and the lab," says George Djorgovski, professor of astronomy and director of CD3. "We believe the joint venture will enable and stimulate new projects and give both campus and JPL researchers a new competitive advantage."

Individually, each center strives to provide the intellectual infrastructure, including expertise and advanced computational tools, to help researchers and companies from around the world analyze and interpret the massive amounts of information they now collect using computer technologies, in order to make data-driven discoveries more efficient and timely.

"We've found a lot of synergy across disciplines and an opportunity to apply emerging capabilities in data science to more effectively capture, process, manage, integrate, and analyze data," says Daniel Crichton, manager of the CDST. " JPL's work in building observational systems can be applied to several disciplines from planetary science and Earth science to biological research."

The Caltech center is also interested in this kind of methodology transfer—the application of data tools and techniques developed for one field to another. The CD3 recently collaborated on one such project with Ralph Adolphs, Bren Professor of Psychology and Neuroscience and professor of biology at Caltech. They used tools based on machine learning that were originally developed to analyze data from astronomical sky surveys to process neurobiological data from a study of autism.

"We're getting some promising results," says Djorgovski. "We think this kind of work will help researchers not only publish important papers but also create tools to be used across disciplines. They will be able to say, 'We've got these powerful new tools for knowledge discovery in large and complex data sets. With a combination of big data and novel methodologies, we can do things that we never could before.'"

Both the CD3 and the CDST began operations last fall. The Joint Initiative already has a few projects under way in the areas of Earth science, cancer research, health care informatics, and data visualization.

"Working together, we believe we are strengthening both of our centers," says Djorgovski. "The hope is that we can accumulate experience and solutions and that we will see more and more ways in which we can reuse them to help people make new discoveries. We really do feel like we're one big family, and we are trying to help each other however we can."

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Kimm Fesenmaier
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Kanamori Wins Milling Medal

Hiroo Kanamori, Caltech's John E. and Hazel S. Smits Professor of Geophysics, Emeritus, was awarded the Marcus Milling Legendary Geoscientist Medal by the American Geosciences Institute at the 2015 American Association of Petroleum Geologists Annual Convention and Exposition. The medal recognizes "scientific achievements and service to the Earth sciences having lasting, historic value."

Kanamori is perhaps best known for developing the moment-magnitude scale, which assigns a magnitude to an earthquake based on the amount of energy it releases and which has replaced the Gutenberg-Richter scale for scientific purposes. His research into the genesis and propagation of a diversity of earthquake types, including slow tsunami earthquakes, megathrust earthquakes, outer-rise earthquakes, and intraplate earthquakes, has helped develop hazard-mitigation plans and real-time early-warning methods.

Kanamori earned his undergraduate and graduate degrees at the University of Tokyo (BS '59, MS '61, PhD '64) before coming to Caltech as a postdoctoral researcher in 1965. After stints at MIT and the University of Tokyo, he returned to Caltech as a full professor in 1972 and became the Smits Professor of Geophysics in 1989. He served as the director of Caltech's Seismological Laboratory from 1990 until 1998 and became the Smits Professor of Geophysics, Emeritus, in 2005.

Kanamori is also a foreign associate of National Academy of Sciences, a member of the American Academy of Arts and Sciences, and a recipient of the American Geophysical Union's Walter H. Bucher Medal and William Bowie Medal and the Inamori Foundation's Kyoto Prize, and he has been declared a member of the Order of the Sacred Treasure, Gold and Silver Star, by the government of Japan.

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Diversity Retreat at Caltech

In September 2013, Caltech, UC Berkeley, UCLA, and Stanford University founded a new consortium—the California Alliance for Graduate Education and the Professoriate (AGEP)—to support underrepresented minority graduate students in the STEM fields of mathematics, the physical sciences, computer science, and engineering. The Alliance, launched through a grant from the National Science Foundation, was created to address the fact that minority students enter STEM fields in disproportionately low numbers and that, as a group, their progress slows at each step in their academic careers.

This April, Caltech was host to "The Next Generation of Researchers," the Alliance's second annual retreat. The retreats are designed to bring together graduate students, postdoctoral fellows, research scientists, and faculty from the four institutions and national labs in California for mentoring and network-building opportunities.

We recently spoke with Joseph E. Shepherd (PhD '81), dean of graduate studies and the C. L. "Kelly" Johnson Professor of Aeronautics and professor of mechanical engineering, about AGEP, the recent retreat, and Caltech's diversity initiatives.

 

What was Caltech's motivation for entering into the California Alliance, and what has the program accomplished so far?

Caltech joined the Alliance to encourage underrepresented minorities to pursue academic careers in mathematics, physical science, computer science, and engineering fields. We seek to not only diversify our own campuses (Caltech, Berkeley, Stanford, and UCLA) but also contribute to diversity throughout the nation.

During the first year, the Alliance members identified participants at the four campuses. We have conducted two retreats—the first at Stanford University in 2014 and the second at Caltech. Graduate students, postdoctoral scholars, and faculty gathered at these retreats and learned about opportunities and challenges for underrepresented minority students transitioning from graduate studies to a career as a faculty member.

In 2014, the Alliance established a postdoctoral scholar fellowship program, accepted applications in the fall, and is in the process of finalizing awards for this coming academic year (2015–16). The Alliance has also accepted applications for the mentor-matching program through which graduate students can visit faculty at Alliance institutions to learn about opportunities and faculty careers in specific research areas.

 

AGEP programs are funded by the NSF. What are they hoping to achieve through these programs?

The AGEP programs were originated at NSF as a response to the recognition of the obstacles that underrepresented minority students faced in graduate education and advancing to faculty careers. These issues are highlighted in "Losing Ground," a 1998 report of a study led by Dr. Shirley Malcom, director of Education and Human Resources Programs of the American Association for the Advancement Science. Dr. Malcolm is a Caltech trustee and was a featured speaker at our 2015 retreat.

 

What are we doing at Caltech to support underrepresented minority students in the graduate sciences, and has anything at Caltech changed as a result of our involvement in this consortium?

The Caltech Center for Diversity has a number of programs that support various segments of our student population, and we are increasing the number of underrepresented minority postdoctoral scholars at Caltech.

In collaboration with several offices across the campus, we are developing and maintaining a strong network focused on outreach, recruitment, matriculation, and the eventual awarding of degrees to underrepresented minorities in the campus' graduate programs.  

Specifically, the Office of Graduate Studies, the Center for Diversity, and the Center for Teaching, Learning, and Outreach focus on programming that creates access to resources, builds community, and leverages relationships to help to address the challenges highlighted in the AGEP program, including facilitated discussion groups that address issues of inclusion and equality, various graduate student clubs that promote cultural awareness and community education, and an annual "Celebration of Excellence" reception to recognize student successes and the efforts of staff, faculty, and students who promote equity and inclusion on campus.

In addition, the graduate recruitment initiative coordinated by the Office of Graduate Studies works to ensure that the campus is able to recruit at underrepresented minority STEM-focused conferences and research meetings around the United States, and encourages graduate student ambassadorship and provides opportunities for underrepresented minority graduate students to network across national professional communities with similar research and academic interests.

 

What can we do better?

Encourage greater diversity in graduate admissions by identifying and recruiting underrepresented minority graduate students and ensuring that every student thrives at Caltech. Encourage more of the current underrepresented minority students and postdoctoral scholars at Caltech to take advantage of the professional development opportunities in the Alliance and facilitate their transition to the next stage of their academic careers. Provide more professional development opportunities for all Caltech students and postdoctoral scholars to learn about academic careers.

 

What was the goal of this year's annual retreat?

One goal was to promote introductions and discussion among students, postdoctoral scholars, and faculty at the Alliance schools. In addition to informal meetings between participants, we held a number of roundtables and panel discussions on topics such as knowing what to expect of grad school, the postdoctoral experience, and, in general, life as a researcher and faculty member. Our retreat highlighted the research between done by faculty, students, and postdoctoral scholars in the Alliance by holding a poster session that enabled the participants to learn about each other's research activity. The retreat participants learned about some of the exciting research being done in protein design at Caltech from the other featured speaker, Steve Mayo (PhD '88), Caltech's William K. Bowes Jr. Leadership Chair of the Division of Biology and Biological Engineering and Bren Professor of Biology and Chemistry.

 

Who were participants in this year's retreat, and what do you think they gained from the program?

There were a total of 111 attendees: 40 percent were faculty, 42 percent were graduate students, 8 percent postdoctoral scholars, and the remainder were staff members, including some from JPL and Sandia National Laboratory.

The participants were recruited by the Alliance leadership at each university. The student participants gained the opportunity to network with scientists and faculty at other Alliance institutions, learned about academic careers and postdoctoral scholar opportunities, and were able engage in wide-ranging discussions about careers in science. The faculty and staff participants were able to provide information and advice to students as well as learn about prospective postdoctoral scholars and faculty members.

In addition, a total of 18 faculty from Caltech participated out of a total of 43 faculty members who attended from all four Alliance universities. The faculty at Caltech are very positive about this program, and we are encouraged by the high level of participation.

 

Were the sessions specifically focused on the particular needs of underrepresented groups?

The focus of the Alliance is on helping young people from diverse backgrounds to consider and succeed in academic careers in science. Many of the issues that contribute to success or failure in academic science careers do not depend on the particular perspective or background of a prospective postdoctoral scholar or professor. The pathway to the professoriate and the mechanics of succeeding in an academic career are far from obvious, particularly for students with disadvantaged backgrounds as well as those who are the first in their family to obtain a college degree or consider a career in science. One of the important roles of the Alliance retreat is in providing information about the many career aspects to which our student participants are exposed early enough in their careers so that it may make a difference. 

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Kathy Svitil
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Mike Brown's "Living Textbook"

Feynman Teaching Award winner Mike Brown ventures into new fields of instruction: the Massive Open Online Course, or MOOC, and the "flipped" classroom, which inverts the traditional arrangement of listening to lectures in class and doing assignments at home.

Mike Brown, the Richard and Barbara Rosenberg Professor and Professor of Planetary Astronomy, is teaching a nine-week course to 20 Caltech undergraduates—and some 2,000 Internet users. Geology/Astronomy 11c, "Introduction to Earth and Planetary Sciences: Planetary Sciences," is also available on line at Coursera.org as "The Science of the Solar System."

"It's pretty amazing," says Brown. In one sitting, I teach more students than I would in my entire career at Caltech."

The course's videos are grouped into four multiweek units that cover the history of water on Mars, the interiors of the giant planets, the formation of the solar system as recorded in the rubble of small bodies left behind, and the search for life beyond Earth. Every lecture demonstrates how planetary science draws on techniques from an assortment of disciplines to attack a problem. For example, he describes how in 1966 Caltech physics professor Robert Leighton (BS '41, MS '44, PhD '47) and planetary science professor Bruce Murray used basic physics to conclude that Mars's polar caps could not be ordinary ice, as had generally been assumed, but must instead be dry ice—frozen carbon dioxide. The unit as a whole traces the history of both the planet and our quest to understand it, from our first telescopic observations to our current fleet of spacecraft. The lectures are sprinkled with personal asides, such as the fact that the very first front-page color photograph to run in Brown's hometown newspaper was of the rusty, rock-strewn desert of Mars's Chryse Planitia, beamed back from the Viking One lander on July 21, 1976.

The for-credit version taken by Caltech undergraduates is a "flipped" class. Students watch the lectures on their own time, and the instructional sessions are devoted to personal interactions with one another and with Brown. After he fields questions on the week's lectures, the students break up into small groups. For the Mars unit, each group was provided the location of one of the backup landing sites selected for Curiosity, the Mars Science Laboratory rover, and told to write a report on the site's geologic history based on the wealth of data and images available online. The reports were to pay special attention to the times and forms in which water might have been present at the sites. Each group then had to make the case for its site as the best choice in a presentation to the entire class.

"The goal is to have them synthesize the individual things they learned from the lectures and apply it to spots that we didn't necessarily talk about," Brown says. "I told them to organize their thinking by just looking at the lectures' titles. There's photogeology, where you compare pictures to landforms on Earth to see what's going on. There are outflow channels, dendritic channels, valley networks. There's the altimetry, which tells you about slopes and drainages. You can look at the gamma-ray data to see if there's subsurface water. And the infrared spectroscopy tells you about the mineralogy, which tells you whether water was present when that rock was laid down. You can apply almost everything that was in the lectures to each of these sites."

After the groups have split up, Brown works the room, listening to the students' discussions and occasionally asking a question. As one group begins pooling what they've gleaned from their individual readings about their site, a student says he doesn't see any evidence for what one paper claims to be an ancient shoreline. Brown remarks, "Just because a paper's been published doesn't mean it's right. How do you decide if a conclusion is credible?" Another student replies, "By how often it's cited?" "That's a good way," Brown agrees. "And it's very easy to do that these days. When I was a student, we had to haul out all these big, thick books. Of course, if all the citations say, 'This is the most idiotic thing I've ever read,' that would be bad." As the period proceeds, the discussion gets more detailed, and Brown's questions become more penetrating. "I'm going to disagree with everything you say to be sure you have the evidence for it," he explains to them. "If I don't ask these questions, NASA will."

This is the second year that Brown has flipped this class. "I'm still learning how it works," he says. When he created the course last year, he recalls, "I spent a lot of time recording. It was a full-time job from January to mid-May, which is crazy for a nine-week class. But the promise was that it all pays off in the subsequent years. Some parts didn't work so well, so I've had to change them, and some parts change because there are always new things happening in space. This time around, I got to put in all the stuff about landing on a comet [i.e., the European Space Agency's Rosetta mission, which landed a probe on comet 67P/Churyumov-Gerasimenko last November], which is super cool, and next year I'll get to do the Pluto flyby stuff [NASA's New Horizons mission, set to flyby the dwarf planet on July 14 of this year]. I think of it as a living textbook."

It took some 45 minutes to record one 15-minute lecture, of which there are about 90. Editing each segment took another two hours. "That was a surprise," Brown says. "At first, I was doing them all myself, but I very quickly cried uncle and sent them over to Leslie [Maxfield (BS '95), Caltech's director of Academic Media Technologies (AMT)]. They did a much better job. This year, with the re-recordings, there's not as much to do, so I'm doing them all myself."

Brown records all the videos in his office using the built-in camera on his computer monitor. In the middle of the room, a portable green-screen backdrop on long-term loan from AMT hangs from borrowed light stands. Hanging next to the screen is the lone blue shirt that Brown wears for continuity. He's perpetually clean-shaven now for the same reason, and he gets the same haircut, on schedule, every eight weeks. "My wife is thrilled," he says. "I used to say, 'Oh, yeah. My hair is 10 feet long; I should get a haircut.' Now she says, 'You're getting another haircut already?'"

Caltech students get nine units of credit for completing the course; people from the outside world get a certificate of completion "good for printing out and hanging on your wall," Brown says. "And as totally meaningless as these certificates are, people are very motivated by them. They're enjoying the class, they're trying to learn, and they want that certificate. I'm very excited about this class because it's the best outreach tool I've ever found, in a very interesting niche where we don't normally do outreach. This is intense—2,000 people spending nine weeks doing three or four hours a week of planetary science. That's crazy. And they were an engaged, dedicated group by the end. They feel a big sense of allegiance to all aspects of it: to me, to Caltech, and I think to Coursera as well. It's a pretty great tool."

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Using Radar Satellites to Study Icelandic Volcanoes and Glaciers

On August 16 of last year, Mark Simons, a professor of geophysics at Caltech, landed in Reykjavik with 15 students and two other faculty members to begin leading a tour of the volcanic, tectonic, and glaciological highlights of Iceland. That same day, a swarm of earthquakes began shaking the island nation—seismicity that was related to one of Iceland's many volcanoes, Bárðarbunga caldera, which lies beneath Vatnajökull ice cap.

As the trip proceeded, it became clear to scientists studying the event that magma beneath the caldera was feeding a dyke, a vertical sheet of magma slicing through the crust in a northeasterly direction. On August 29, as the Caltech group departed Iceland, the dike triggered an eruption in a lava field called Holuhraun, about 40 kilometers (roughly 25 miles) from the caldera just beyond the northern limit of the ice cap.

Although the timing of the volcanic activity necessitated some shuffling of the trip's activities, such as canceling planned overnight visits near what was soon to become the eruption zone, it was also scientifically fortuitous. Simons is one of the leaders of a Caltech/JPL project known as the Advanced Rapid Imaging and Analysis (ARIA) program, which aims to use a growing constellation of international imaging radar satellites that will improve situational awareness, and thus response, following natural disasters. Under the ARIA umbrella, Caltech and JPL/NASA had already formed a collaboration with the Italian Space Agency (ASI) to use its COSMO-SkyMed (CSK) constellation (consisting of four orbiting X-Band radar satellites) following such events.

Through the ASI/ARIA collaboration, the managers of CSK agreed to target the activity at Bárðarbunga for imaging using a technique called interferometric synthetic aperture radar (InSAR). As two CSK satellites flew over, separated by just one day, they bounced signals off the ground to create images of the surface of the glacier above the caldera. By comparing those two images in what is called an interferogram, the scientists could see how the glacier surface had moved during that intervening day. By the evening of August 28, Simons was able to pull up that first interferogram on his cell phone. It showed that the ice above the caldera was subsiding at a rate of 50 centimeters (more than a foot and a half) a day—a clear indication that the magma chamber below Bárðarbunga caldera was deflating.

The next morning, before his return flight to the United States, Simons took the data to researchers at the University of Iceland who were tracking Bárðarbunga's activity.

"At that point, there had been no recognition that the caldera was collapsing. Naturally, they were focused on the dyke and all the earthquakes to the north," says Simons. "Our goal was just to let them know about the activity at the caldera because we were really worried about the possibility of triggering a subglacial melt event that would generate a catastrophic flood."

Luckily, that flood never happened, but the researchers at the University of Iceland did ramp up observations of the caldera with radar altimetry flights and installed a continuous GPS station on the ice overlying the center of the caldera.

Last December, Icelandic researchers published a paper in Nature about the Bárðarbunga event, largely focusing on the dyke and eruption. Now, completing the picture, Simons and his colleagues have developed a model to describe the collapsing caldera and the earthquakes produced by that action. The new findings appear in the journal Geophysical Journal International.

"Over a span of two months, there were more than 50 magnitude-5 earthquakes in this area. But they didn't look like regular faulting—like shearing a crack," says Simons. "Instead, the earthquakes looked like they resulted from movement inward along a vertical axis and horizontally outward in a radial direction—like an aluminum can when it's being crushed."

To try to determine what was actually generating the unusual earthquakes, Bryan Riel, a graduate student in Simons's group and lead author on the paper, used the original one-day interferogram of the Bárðarbunga area along with four others collected by CSK in September and October. Most of those one-day pairs spanned at least one of the earthquakes, but in a couple of cases, they did not. That allowed Riel to isolate the effect of the earthquakes and determine that most of the subsidence of the ice was due to what is called aseismic activity—the kind that does not produce big earthquakes. Thus, Riel was able to show that the earthquakes were not the primary cause of the surface deformation inferred from the satellite radar data.

"What we know for sure is that the magma chamber was deflating as the magma was feeding the dyke going northward," says Riel. "We have come up with two different models to explain what was actually generating the earthquakes."

In the first scenario, because the magma chamber deflated, pressure from the overlying rock and ice caused the caldera to collapse, producing the unusual earthquakes. This mechanism has been observed in cases of collapsing mines (e.g., the Crandall Canyon Mine in Utah).

The second model hypothesizes that there is a ring fault arcing around a significant portion of the caldera. As the magma chamber deflated, the large block of rock above it dropped but periodically got stuck on portions of the ring fault. As the block became unstuck, it caused rapid slip on the curved fault, producing the unusual earthquakes.

"Because we had access to these satellite images as well as GPS data, we have been able to produce two potential interpretations for the collapse of a caldera—a rare event that occurs maybe once every 50 to 100 years," says Simons. "To be able to see this documented as it's happening is truly phenomenal."

Additional authors on the paper, "The collapse of Bárðarbunga caldera, Iceland," are Hiroo Kanamori, John E. and Hazel S. Smits Professor of Geophysics, Emeritus, at Caltech; Pietro Milillo of the University of Basilicata in Potenza, Italy; Paul Lundgren of JPL; and Sergey Samsonov of the Canada Centre for Mapping and Earth Observation. The work was supported by a NASA Earth and Space Science Fellowship and by the Caltech/JPL President's and Director's Fund.

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Kimm Fesenmaier
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Tuesday, May 26, 2015 to Friday, May 29, 2015
Center for Student Services 360 (Workshop Space) – Center for Student Services

CTLO Presents Ed Talk Week 2015

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