Studying Volcaniclastic Deposits Northern Patagonia, Chile

USGS research hydrologist Tom Pierson, working with geologists from SERNAGEOMIN (Chile's geological survey), examines lahar and volcanic flood deposits along Rio Chaitén, approximately 8 km downstream of Chaitén volcano. The rhyolite volcano's current eruptive phase began in May, 2008, producing several pyroclastic flows and widespread ashfall. Lahars and sediment-rich floods were triggered by the first few centimeters of post-eruption rainfall, sweeping down the steep ash-covered slopes of the volcano, completely filling the original course of the Chaitén River, before flooding and burying Chaitén town (10 km from the volcano) in sediment. By studying these deposits and interpreting how sediments are mobilized and emplaced during and following eruptions, scientists are gaining a better understanding of how volcanoes can trigger life-threatening volcano-hydrologic hazards downstream of active volcanoes.