Sibayak and Mt. Pinto are located within the Singkut caldera in NE Sumatra. The slightly higher Pinto partially overtops the 900-m-wide crater of Sibayak to the N. The summit contains a lava dome and an area of hydrothermal alteration visible in this photo. An ash eruption from Sibayak was recorded in 1881, and nearby residents have legends of eruptions.

Photo by Tom Casadevall, 1987 (U.S. Geological Survey).

This image is made available as a Public Domain Work, but proper attribution is appreciated.

Keywords: hydrothermal alteration

Singkut