From one volcano to another!

We are on on Mount Sibayak (Indonesian: Gunung Sibayak) an active Pleistocene-to-Holocene stratovolcano peaking at 2,181 m (7,156 ft). The other volcano is Mount Sinabung, about 15km to the southwest, that in 2010 erupted after a 400-year-long hiatus, a blink of an eye in geological time.

Both volcanoes are part of the Barisan Mountain range that runs NW-SE for a 1000 miles along the whole length of Sumatra parallel to the Sumatra Trench & includes 35 active volcanoes.

Although its last eruption was more than a century ago, Sibayak has geothermal activity in the form of steam vents and hot springs on and around the volcano. The vents produce crystalline sulfur, which was being mined on a small scale in 1979 (men carrying sacks down the mountain on their backs). Seepage of sulfurous gases has also caused acidic discolouration of the small crater lake part of which can be seen bottom middle.