Several phreatic explosions occurred at Lascar daily during 18-21 April. The explosions produced plumes of gas and small amounts of ash, with the highest rising plumes reaching 3 km above the volcano (or 28,200 ft a.s.l.) on the 18th and the 21st. Ash was deposited on the volcano's flanks as far as 3 km from the summit. There was no evidence of new magma reaching the surface and recorded seismicity was inferred to be related to shallow degassing. The Buenos Aires VAAC released volcanic ash advisory statements during the report period.

Geological Summary. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Sources: Buenos Aires Volcanic Ash Advisory Center (VAAC), Jorge Clavero-Chilean Geological Survey (Sernageomin) and Juan Cayupi-Chilean Emergency Office (ONEMI) via the Volcano Listserv