October 13, 2000 Eruption of Altar

No eruption

This report is based on field work conducted at Altar during 23-25 October. At 0558 on 13 October a large block of andesitic breccia with a volume of ~1.5 x 10 m broke from the N wall of La Monja Grande (The Great Nun), a snow- and ice-covered peak near the summit of the Plio- Pleistocene stratovolcano Altar. The catastrophic fall was likely facilitated by frost wedging that slowly developed and enlarged fractures throughout the rock. The block fell 900 m and landed in the E end of Laguna Amarilla (Yellow Lagoon) within the summit caldera. The impact to the lake generated an initial wave 50 m in height and smaller successive waves that ejected 1.5-3.0 x 10 m of water and sent it hurtling down the W side of the mountain. (reference #14372)

According to local witnesses, shortly before 6 a.m., in the morning of Friday the 13th of October 2000, a giant explosive sound was heard from the inner part of the volcano. Shortly after, a giant water wave overflow the fifty meters high wall from the western side of the glacial Lake Laguna Amarilla forming downstream a debris avalanche in the Valley of Collanes within the Río Blanco river, until it reached the confluence with the Río Tarau river. According to Civil Defense reports at the time, more than 400 families were affected, 10 people disappeared, 10 homes were destroyed, while 200 head of cattle were lost and some 600 hectares of crops were destroyed. (reference #14371)