Global Volcanism Program | Image GVP-03713
An aerial view from the east shows the steaming 1991 andesitic summit dome and the fumarolic area located in the 1987 phreatic pit directly east of the dome. The pinkish deposits in center of the photo are hydrothermally altered, highly unstable areas of the summit similar to those that failed gravitationally to the south on April 16. This produced a large quantity of very fine pinkish-to-yellowish ash, which formed voluminous billowing clouds rising above the April 16 pyroclastic flows.
Photo by Claus Siebe, 1991 (Universidad Nacional Autónoma de México).