The last report discussed observations of ash plumes and MODVOLC thermal alerts at Sangay through February 2010 (BGVN 35:01). Intermittent reporting indicated that similar activity continued through at least February 2011, with plumes reaching up to 7.6 km altitude (table 7). Clouds obscured the view at times, and plumes were reported primarily by pilots and were sometimes visible on satellite imagery.

Table 7. Plumes reported at Sangay during April 2010-February 2011. No plumes were noted during March 2011. Courtesy of the Washington VAAC.

On 5 December 2010, the Washington Volcanic Ash Advisory Center (VAAC) stated that Instituto Geofisico reported elevated seismicity.

The MODVOLC alert system issued thermal alerts for Sangay monthly during March 2010 through early October 2010. Then, alerts were absent until 11 January 2011 (table 8).

Table 8. Thermal alerts issued for Sangay by the MODVOLC system during March 2010-20 March 2011 (continued from the list in BGVN 35:01). The system uses the MODIS instrument on the Terra and Aqua satellites. Courtesy MODVOLC Thermal Alerts System.

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: Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).