SERNAGEOMIN reports through 12 July 2008 indicated that the eruption at Chaitén was continuing, although poor weather conditions made visual observations difficult. However, explosion plumes were seen on some occasions. Volcano-tectonic (VT) earthquakes continued, concentrated on the E and SE crater rim. Seismicity doubled during 10-12 July, and some VT events were greater than M 2.2.

Ash advisories issued by the Buenos Aires VAAC noted continuous emissions based on webcam observations during 9-11 July, but plumes could not be seen in satellite imagery.

Geological Summary. Chaitén is a small, glacier-free caldera with a compound Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. Early work had identified only a single explosive eruption during the early Holocene prior to the major 2008 eruption, but later work has identified multiple explosive eruptions throughout the Holocene. A rhyolitic obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km from the volcano to the N and S. The caldera is breached on the SW side by a river that drains to the bay of Chaitén. The first historical eruption, beginning in 2008, produced major rhyolitic explosive activity and growth of a lava dome that filled much of the caldera.

Sources: Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Nacional de Geología y Minería (SERNAGEOMIN)