A recent expedition, 28 July-9 August, to the stratovolcano Sangay reports the following activity.

Mild explosive activity occurred at intervals of 6-12 hours with the expulsion of white, vapor-rich, sulfurous plumes that rose approximately 100 m. Very acidic rains were falling W of the cone. The NW side of the cone was covered by still-hot lava flows (basaltic andesite) from the last few years. A new lava flow was leaving the S crater and has descended W several hundred meters. A light coating of ash covered the snow on the SW side of the cone. No other activity was observed on the other sides of the volcano. It appeared that this activity has continued steadily from last year. A small parasitic cone of approximately 50 m height was recently discovered on the lower E flank. It is not presently active.

On 10 August an independent British team, which apparently included no geologist, reached the 3,700 m basecamp level on the volcano. Two days later six members ascended to within 300 m of the summit. At 1230 an explosion produced a black mushroom cloud that reached an estimated 300 m above the volcano and dropped ejecta (to 35 cm) on the group. Later, search parties found three injured, one dead, and another had not been found 5 days after the accident. Helicopter rescue attempts were abandoned on 18 August after two days of heavy snowfall.

Geological Summary. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: M. Hall, Escuela Politécnica Nacional, Quito; J. Aucott, British Embassy, Quito.