Tewksbury’s geological research aims to find answers in ancient patterns
By Nora Grenfell ’12
Since the Jan. 12 earthquake that devastated Haiti, several other quakes have sent seismic ripples across the Earth and the media. In April, a volcano brought European travel to a halt, costing the airline industry more than $1.7 billion. With such events packed closely together, many people — big-screen cataclysms like 2012 and The Day After Tomorrow fresh in their minds — are wondering how soon to expect doomsday. Barbara Tewksbury, the Upson Chair for Public Discourse and professor of geosciences, offers a more enlightened view.
“To geologists, big quakes are never a surprise,” Tewksbury says. Earthquakes, like many natural disasters, present such a large problem in part because they are incredibly difficult to predict. Earthquakes have been occurring for much longer than geologists have been studying them with good technology, and recurrence patterns of certain faults may span generations of human life. Although some faults may be more likely than others to slip and cause an earthquake, timing and magnitude are hard to anticipate. “It’s not very clear how a huge earthquake is going to influence the next couple of decades,” Tewksbury explains.
In fact, the fault that most geologists thought would slip in Haiti was not the one that caused the magnitude 7.0 earthquake in January. Could the predictions of geologists have been more precise, allowing the Haitian government to better prepare for a disaster? Tewksbury suggests that, while certain preparation measures can always be taken, without more research and better technology, it is close to impossible to predict the exact time and place an earthquake will occur. Indeed, earthquakes can also occur in areas that completely elude both contemporary and historical research. In 1811 and 1812, hundreds of earthquakes, two with magnitudes greater than 8.0, rocked Missouri. There were no fatalities because there were no tall buildings yet constructed in St. Louis. “If another earthquake happens in our midcontinent region, we’re going to be unprepared for it, too,” Tewksbury says. “How could you possibly prepare for something as devastating as a magnitude-9 quake under St. Louis? It would be an economic disaster in the United States.”
In high-risk areas like California, building codes and laws have made a difference in limiting the damages and casualties from earthquakes, but Tewksbury points out that while California has taken effective preventive measures, “there hasn’t been a magnitude-9 earthquake in California since 1906.” And areas that are at lower risk based on the infrequent historical occurrence of earthquakes lack the laws and building codes that could limit the scope of a humanitarian disaster if a quake were to strike.
Rare opportunity in Iceland
Another example of geologic unpredictability is the recent eruption of Eyjafjallajokull. Tewksbury is currently conducting research in Iceland that dates back to the late Pleistocene (1.8 million to 10,000 years ago), but it might pertain to a volcano that’s active right now. Her work examines formations in Iceland composed of a type of volcanic debris called hylaoclastites. Until now, the formations have been recognized as solid rock material. Tewksbury, however, has identified the formations as deformation bands of loose material that has been consolidated over time. The consolidated material is unique because it erupted under glacial ice, and the incredible pressure from the glacier caused it to compact into solid rock.
Iceland sits on a spreading ridge, where two tectonic plates diverge in a sub-Arctic climate. As the plates move apart, magma flows up from the Earth’s crust, erupting in volcanoes. This unique confluence of geologic factors creates a land of ice and fire: lava-spewing volcanoes that are buried under kilometers of glacial ice. This environment presents opportunities for geologic study that are rare on the planet.
When volcanoes erupt under glaciers, they deposit material like Tewksbury’s hylaoclastites. When the pressure of the glacier begins to affect the unconsolidated materials, the grains push into one another and the rocks become compacted. Over time, the fragile material that has not consolidated wears away, leaving peculiar-looking outcrops of solid rock.
Tewksbury points out that while there’s no immediate “economic value” to her work — it’s not like looking for oil or natural gas — it’s part of a large and important puzzle. The ultimate goal of her research is to construct a timeline of the collapse of the outcrops. In mapping the patterns of eruption and adjustment of this volcanic debris, Tewksbury and her colleagues may be able to determine how this region of southwestern Iceland looked in the past and what geologic changes have occurred since then.
The “holy grail” of Tewksbury’s research would be using the chronology of the outcrop to determine the thickness of the glacier that rested on top of this area. Measuring the thickness and melting rate of glaciers is an especially important topic in geologic and environmental research today. Although she has yet to determine how to use these outcrops to evaluate paleo-ice thickness, Tewksbury believes the modern eruption might illuminate her research, as geoscientists can test the thickness of the ice at Eyjafjallajokull.
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When fire meets ice
Eyjafjalla is a large glacier in southwestern Iceland, underneath which there is an active volcano. These “subglacial” volcanoes are more common in Iceland than anywhere else in the world, but even in Iceland they are not widely studied. Volcanologists had long predicted that Eyjafjalla’s subglacial neighbor Katla would be the first to erupt and trigger massive flooding—but they were proven wrong on March 20. Eyjafjallajokull, which means “ice-mountain-glacier” in Icelandic, was host to a series of earthquake swarms and finally an eruption. Residents in many areas of southwestern Iceland were evacuated, and the eruption had an unforeseen and calamitous effect on airline travel across Europe.
“Right now there should be some of this forming where Eyjafjallajokull erupted,” Tewksbury explains. “We keep nudging our Icelandic colleagues about whether we can get some samples from the current eruption before the stuff gets solidified — but it’s a little dangerous now!”
In places like Egypt (where Tewksbury is also conducting research) these types of deformation bands occur because of tectonic activity deep beneath the surface. In Iceland, however, these deformation bands form as a result of pressure from the ice above, not plates below. Because the conditions for deformation bands are so specialized — and usually occur due to tectonic activity — no one had thought to look for them in Iceland. The majority of geologists in Iceland specialize in volcanoes; fewer study subglacial volcanism, and hardly any study structural geology. Deformation bands are a rarity, and even structural geologists sometimes have trouble recognizing them.
Tewksbury was in Iceland in 2005 leading a field study for several students from Hamilton and SUNY Oneonta when she saw these structures in a new light. She recalls, “I’d been reading about deformation bands for my structural geology class. I was standing in front of this outcrop I’d seen many times before, and one of my structural students was standing next to me and I said, ‘Will, those look like deformation bands!’ and he looked up at me and said, ‘Can that be my senior project?’”
Nora Grenfell ’12 spent the summer entrenched in the history of the College as an intern in the Office of Communications and Development. After a brief hiatus for field study in Iceland, she is working toward a major in comparative literature and a minor in geosciences. Nora serves as a tutor at the Nesbitt-Johnston Writing Center and as production editor for The Spectator.