Download The Earth`s Fastest Growing Volcano

The Earth’s
Fastest Growing
Volcano BY NEALEY SIMS Something big is happening underneath Uturuncu volcano in Bolivia. The volcano, while still active, hasn’t erupted in over 300,000 years, yet the ground beneath it is inflating at an alarmingly fast rate. “Whatever is causing it, it’s happening somewhere deep below the surface,” says Nealey Sims, a physics student at the University of North Alabama who is working as an intern in Fairbanks, Alaska this summer. Sims is working on a project to help shed light on what is going on underneath this intriguing volcano. Uturuncu is one of many volcanoes located on what is known as the Altiplano-­‐Puna Volcanic Complex in South America. This is a volcanic arc associated with the subduction, or sinking, of the Nazca plate under the South American plate. According to recent studies, the volcano is deforming rapidly, a process denoted by surface changes around the volcanoes; in this case, a central uplift rate of 1-­‐2 cm/yr has been observed around Uturuncu. Sims is not studying the volcano itself, though, but rather the rocks deep beneath it in a layer of the Earth beneath the crust known as the mantle. This layer is constantly “flowing” while at the same time remaining solid rock. “Our goal is to try to determine what direction the mantle beneath Uturuncu is flowing in hopes that it will help us understand the processes contributing to the volcano’s rapid deformation,” says Sims. So how does one figure out what’s happening so deep in the Earth? One of the most useful tools for doing this is an earthquake. Earthquakes are made up of waves: a primary wave, or p-­‐wave, and a secondary wave, or s-­‐
wave. Geophysicists use seismometers, highly sensitive instruments buried in the ground, to detect the waves as they move through the Earth. According to Sims, by studying how long it takes certain waves to reach the seismometer from the earthquake location, geophysicists can infer something about the material through which it traveled. “We are looking at s-­‐waves in particular to study the anisotropy of the mantle beneath Uturuncu,” says Sims. Anisotropy means that a material doesn’t have identical properties in all directions. Consider trying to put a circle block into a circle hole. No matter which way you turn the block it will fit. This represents isotropy; it doesn’t matter what direction the block travels, it will reach the other side all the same. Now try putting a triangle block into a triangle hole. If the points aren’t aligned, it will not fit. The hole is directionally dependent; this is anisotropy. Waves behave similarly only instead of stopping at the anisotropic material, the waves split into two components, a fast and a slow direction, as shown in the figure below. Wave traveling through anisotropic medium. Credit: http://geophysics.eas.gatech.edu/classes/Geophysics Geophysicists can look at the time difference between the two components recorded on the seismometer to determine which direction is faster. Generally, the fast direction corresponds the direction of flow beneath the surface. “I believe that studying the flow of mantle beneath the volcano will provide insight into not only what is causing present deformation,” says Sims, “but also what activity we can expect from Uturuncu in the future.” References: R. Stephen J. Sparks and others (2008) "UTURUNCU VOLCANO, BOLIVIA: VOLCANIC UNREST DUE TO MID-­‐CRUSTAL MAGMA INTRUSION", American Journal of Science, Vol. 308, June, 2008, P. 727–769, DOI 10.2475/06.2008.01