Guagua Pichincha Volcano, north central Ecuador (0.17°S, 78.60°W). All times are local (GMT −5 hours).

A small phreatic explosion that probably occurred in mid-August deposited fine tephra as much as 1 km southeast of three new vents (3–8 m in diameter) in the summit crater. The new vents formed just east of a lava dome, about 400 m in diameter, emplaced in the center of the summit crater, probably in 1660. Pichincha's horseshoe-shaped summit crater, about 2 km in diameter and 600 m deep, occupies the west end of a 9-km-long massif and is breached to the west, in the opposite direction from Ecuador's capital Quito (population 600,000), which is located at the east foot of the volcano. Aerial observers reported increased fumarolic activity in the summit crater about August 20. Plume heights of as much as several hundred meters were reported in mid-August, and a group that climbed the volcano in early September observed a 200- to 300-m-high plume, but vapor emission had declined to only 2–3 times its normal level by early October. Temperatures of summit crater fumaroles in early October were 88°–90°C, comparable to those recorded in 1976.