Elyse Williamson '10 and Professor Tewksbury Explore Iceland's Volcanoes
During the last Ice Age, the whole country of Iceland was covered in a thick sheet of ice. From an aerial view, most of the island would have appeared to be in a state of frigid serenity. But under the ice, chaos ensued – massive volcanoes entombed in the ice erupted often, causing the overlying ice to melt. As the hot lava erupted into cold water, explosions occurred, depositing fragmented rock and glass with few lava flows.
These unusual rocks are still abundant in Iceland today. Elyse Williamson '10 is working with Upson Chair for Public Discourse and Professor of Geosciences Barbara Tewksbury to analyze well-exposed areas of subglacially erupted rock and to study a particular kind of structure known as deformation bands, which occur commonly in these rocks but have not been studied before.
Tewksbury says that Iceland is very volcanically active because the plate boundary between the North American Plate and the Eurasian Plate runs right through Iceland, and new volcanic material comes up to make new crust. This makes Iceland one of the only places on the planet that one can see two plates diverging above the surface of the ocean.
Many people confuse Iceland with Greenland and assume that the country is desolate. On the contrary, the countryside is not as barren as Greenland, and in fact, parts of Iceland are very vibrant and grassy. Most people do live in the greater capitol city area, though, because "it is hard to get to some of the central areas without four-wheel-drive." Despite the remoteness of the area they are looking at, this is the third summer she has taken a student there to do field work.
The first season was the summer of 2005. This year, Tewksbury and Williamson want to observe some of the rocks surrounding the Hekla Volcano located in south central Iceland.
The deformation bands that they will be studying are harder and stiffer than the surrounding rock and tend to stick up as fins above the surface of the rock. They look very much like veins that occur commonly in other kinds of rocks. Deformation bands and veins are, however, very different kinds of structures.
"You can imagine if you have a really porous rock, kind of like weakly glued-together Cheerios, and you wanted to shift one side of the block of Cheerios with respect to the other, you could either cut it and make a fault through it or you could move one side against the other and cause all of the cheerios to crush, collapse and fill in all of the pore spaces," Tewksbury explained. "Sort of like Rice Krispie treats, too. You'd get one side to shift relative to the other without a through-going fracture [characteristic of a fault], but you'd have this band in the center where are the grains were crushed and all the pore space has collapsed."
In other words, the melting ice caused the deformation bands in the subglacial rocks to form as the volcanic pile slumped and adjusted. Because the deformation bands are harder than the surrounding rock, they stick up as fins when the rest of the rock erodes away.
In addition to studying the distribution of deformation bands along a volcanic ridge north of Hekla, they will also look at glacier burst deposits in South Iceland, which may also contain deformation bands. Glacier bursts occur when the water melted by an eruption floats the edge of the glacier and bursts out from under the ice sheet, carrying with it lots of sediment. Although the chances of finding deformation bands in these are slim, studying these deposits will provide an important confirmation of models that she and her students have developed so far or a pivot point from which they can modify and re-analyze their ideas.
Once they have collected sufficient samples and data, the two researchers will bring the rocks back to Hamilton to analyze under the microscope. The rocks they will look at were significantly altered very shortly after eruption. "It turns from pristine black pumice, ash, and rock fragments to kind of a Dijon-mustard colored rock called palagonite," Tewksbury clarified. "It's quite spectacular under the microscope though, even if it doesn't look so appealing in the field."
In some ways, process is just as much fun as the results. Field work is something both professor and student can appreciate. "There's nothing like doing field work," Tewksbury said. "It's really exciting to be out there, to be confused half the time, and to be trying to figure out what the rocks are telling you."
Williamson says that she is excited to be part of this project. For the past two summers she has gone to the Greenland Ice Sheet to do research with the Cold Regions Engineering Lab in Hanover, N.H. There she measured firn (snow more than one year old) properties to help aid in the interpretation of past atmospheric gases in ice cores. Her work this summer will further add to her geosciences résumé. She knows that she wants to do something with geosciences for a career, but is unsure what avenue she will pursue.
Regardless of what she decides, Williamson seems to be a natural-born geologist. A self-proclaimed outdoors-y person, she is an avid tennis player and runner. In her spare time she also enjoys hiking and playing on Hamilton's popular intramural sports teams.
-- by Allison Eck '12
Summer Research at Hamilton