Perbakti-Gagak

Geography & Climate

Perbakti-Gagak is located in Indonesia, within the Sunda Volcanic Arc of the broader Sunda-Banda Volcanic Regions. Situated at 6.75° S, 106.67° E in the Southern Hemisphere, the volcano lies within a tropical climate zone. With a summit elevation of 1,726 meters above sea level, Perbakti-Gagak is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Perbakti-Gagak sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Indonesia near Perbakti-Gagak, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Perbakti-Gagak has 7 recorded eruptions in the geological database, spanning from 6450 BCE to 1939 CE. The most powerful recorded event was a gentle, effusive event in 1939 CE, reaching VEI 1 on the Volcanic Explosivity Index. This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. The most recent eruption in 1939 CE places this volcano within the modern era of volcanological observation.

Significance

With 7 recorded eruptions on file, Perbakti-Gagak has enough documented activity to help scientists identify patterns in its eruptive behavior.

GVP Reference Summary

The Perbakti-Gagak volcanic complex, also known as Kiaraberes-Gagak, is a cluster of deeply eroded stratovolcanoes situated immediately SW of Salak volcano. The summit ridge of Gunung Perbakti is elongated in a NW-SE direction, and Gunung Endut volcano rises above a saddle to its SW. Gunung Gagak, to the NW, is capped by pumice and obsidian, with obsidian lava flows extending N and NE. Quaternary rhyolitic lava domes form a NNE-trending chain at the eastern side of the complex. Two 2-km-wide depressions on the northern and southern sides of Perbakti form the headwaters of the Kaluwung Herang and Pamatutan rivers, respectively. The complex is marked by vigorous geothermal activity. Fumaroles, mud pots, and hot springs are located on the S and SE flanks of Perbakti and at the Kiaraberes area, which includes the commercial geothermal field of Awibengkok. Mild phreatic eruptions took place during the Holocene into historical time from flank fumarolic fields.

— Smithsonian Institution, Global Volcanism Program