I may do most of my work in the lab, but my research starts in the field, at actual volcanoes. I study two volcanoes: Mount Vesuvius in Italy and Mount St. Augustine in Alaska. Both these volcanoes erupted explosively many times. They're both found above subduction zones, places where the edge of one tectonic plate is sinking underneath another. The explosion of Mount Vesuvius in A.D. 79 buried the cities of Pompeii and Herculaneum with mud and ash.   Mount St. Augustine is part of the Ring of Fire, a chain of volcanoes circling the Pacific Ocean. It has erupted twice since 1969. I hope to discover what makes these types of volcanoes explosive. I start by collecting pumice, a light rock filled with holes like a sponge. Pumice forms from explosive eruptions. The lava flows during these eruptions are foamy from all the gas. The frothy liquid cools very quickly. When it hardens, the bubbles in the lava become holes in the solid rock. In fact, there are so many holes that pieces of pumice actually float on water!