IG reported that tremor at Sangay ceased on 10 March and the number of long-period earthquakes began to decline the next day. The number of explosions per day increased (from a maximum of four during 3-11 March) to 10 on 12 March, peaked at almost 110 on 15 March, and then declined to 50 on 17 March. Cloud cover prevented views of the volcano though the seismic data suggested that gas-and-ash emissions were produced; ashfall was not reported in towns downwind. At 0400 on 17 March continuous tremor with interspersed bursts of more intense tremor began to be detected. The activity intensified at 1300, and then began to gradually decline. IG noted that climbers should avoid the volcano during periods of increased activity.

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.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)