Buyan-Bratan

Geography & Climate

Buyan-Bratan is located in Indonesia, within the Sunda Volcanic Arc of the broader Sunda-Banda Volcanic Regions. Situated at 8.28° S, 115.13° E in the Southern Hemisphere, the volcano lies within a tropical climate zone. At 2,244 meters above sea level, Buyan-Bratan rises above the surrounding terrain into montane or subalpine conditions. The elevation creates distinct ecological zones along its flanks, from forested lower slopes to exposed rocky terrain near the summit. The volcanic landform is characterized as a cluster, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Buyan-Bratan 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 Buyan-Bratan, 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.

GVP Reference Summary

The most obvious feature of the Buyan-Bratan volcanic complex in north-central Bali is the 11 x 6 km wide Bratan caldera (also known as Catur or Tjatur caldera), which contains three caldera lakes. Several post-caldera stratovolcanoes straddle its southern rim; the largest post-caldera cone, Batukau (Batukaru), is 10 km SW. The cones are well-formed, but covered with thick soils and vegetation; they are thought to have been inactive for hundreds or thousands of years (Wheller, 1986). The Tapak and Lesong cones are not covered by deposits of the youngest dacitic pumice eruptions of nearby Batur volcano, and are thus thought to be less than 23,000 years old. The geothermal field within the caldera has been developed to produce electrical power, and hot springs are located in more than a dozen locations.

— Smithsonian Institution, Global Volcanism Program