Volcano Type: Stratovolcano
Volcano Status: Holocene
Last Known Eruption: Unknown
Summit Elevation: 5697 m 18,691 feet
Latitude: 25.17°S 25°10’0″S
Longitude: 68.50°W 68°30’0″W
The NNW-trending edifice of 5697-m-high Lastarria volcano along the Chile-Argentina border contains five nested summit craters. The youngest feature is a lava dome that overlaps the northern crater rim. The large andesitic-dacitic Negriales lava field on the western flanks was erupted from a single SW-flank vent. A large debris-avalanche deposit is found on the SE flank. Recent pyroclastic-flow deposits form an extensive apron below the northern flanks of the volcano.
Although no historical eruptions have been recorded, the youthful morphology of deposits suggest that Lastarria has been active during historical time. Persistent fumarolic activity occurs at the summit and NW flank, and sulfur flows have been produced by melting of extensive sulfur deposits in the summit region.
A pre-historic collapse occurred on the southeast flank of Lastarria volcano. The debris avalanche climbed and over-rode an older scoria cone 125 m high, located due east of Lastarria, before coming to rest. The avalanche has an unusually high velocity of 300 km/hr. At Lastarria, the detached mass was fluidised and incoherent, unlike Mt St Helens, which consisted of large coherent blocks, composed of interleaved lavas and pyroclastic layers.
Lastarria volcano is one of the few locations where sulphur flows have occurred. Sulphur usually flows as a Newtonian fluid, but the presence of gas bubble and crystals at Lastarria sulphur flows indicated it may have behaved as a Bingham fluid.
Originally posted 2010-11-04 03:59:36.
