Contributed by Meghan Guild with assistance from Kara Brugman.
Hello from the Experimental Petrology and Igneous processes Center (EPIC) at Arizona State University. In our lab, we study how magma forms by simulating pressures and temperatures of the Earth’s interior. Outside of the lab, we travel the world to study the various geologic settings we recreate everyday in the lab.
Visting A Paleo-Subduction Zone
In May 2015, I traveled to Japan, accompanied by Christy (Principal Investigator) and Michael (Lab Manager), to collect rock samples that would help me address fundamental questions about subduction zone processes and arc magma genesis. The rocks from the Higashi-akaishi peridotite that were once deep in a subduction zone but now sit exposed on the Earth’s surface at 1700m. Our steep and strenuous trek to the targeted outcrops essentially traced the path of the subducting slab into the mantle—a unique and generally inimitable experience. Our colleague, Tomoyuki Mizukami, from Kanazawa University, has a wealth of experience in this region and guided us to the high-pressure rocks. We were able to collect and carry ~100 kg of the densest rocks on Earth, which proved to be a challenge—but so worth it!
Visiting Active Volcanoes in Japan, Including Mount Aso (aka Aso-san)
After we parted ways with our Japanese colleagues we explored the volcanoes of the Japanese island arc. One of the largest and most active volcanoes in the world, Aso-san, lies in the center of Kyushu, Southern Japan. The Aso caldera is impressively large (25km north-south and 18 km east-west) and formed during a series of violently explosive pyroclastic volcanic eruptions between 270 ka and 90 ka years ago.
In comparison, the Yellowstone Caldera in Wyoming is about 45 by 85 km and experienced its last caldera-forming eruptions 631 ka. The pyroclastic eruptions that form calderas are particularly dangerous because of the amount of superheated ash and gases they release. After columns of gas and particulates are propelled into the stratosphere, the ash can circulate in the upper atmosphere for weeks and could affect global climate for years. These columns eventually collapse under their own weight into pyroclastic flows—fast-moving currents of hot tephra that rush down the sides of the volcano, destroying everything in their path. After this main eruptive phase, post-caldera eruptions can continue for hundreds of thousands of year, although at Yellowstone, these eruptions were generally less violent and the products were more traditional lavas instead of ash flows.
Post-caldera forming at Aso eruptions have been ongoing from 90 ka to present evidenced by the 17 visible volcanic cones found within the caldera walls. The active central cone of Aso caldera, Nakadake Volcano, has been erupting since 22 ka. The 1506 m high edifice is a composite cone composed of basaltic-andesite to basalt. We stayed at the base of Aso (nestled in the massive caldera). It was incredible to be surrounded by fresh volcanics and observe the periodic puff of gas and ash from Nakadake. Because of this small but persistent activity we were unable to get as close as we would have liked—something about volcanic gas emissions being toxic…
Of late, Nakadake has been relatively quiet until an unanticipated explosion at 09:43 (local time) on Monday September 14, 2015, which produced a column of ash that rose 2 km above the crater and subsequently collapsed into a small pyroclastic flow. The ash dispersal led to a number of flight cancellations but no one was hurt. I am sorry that we missed the eruption during our visit, but a landscape I observed only 3 months ago has already changed—and that is pretty awesome!
Eruption video: https://www.youtube.com/watch?v=yYS2JFWHT0c
You can keep an eye on the ongoing activity at Aso at this website: http://www.volcanodiscovery.com/aso/news.html.