Krakatau

Geography & Climate

Krakatau is located in Indonesia, within the Sunda Volcanic Arc of the broader Sunda-Banda Volcanic Regions. Situated at 6.10° S, 105.42° E in the Southern Hemisphere, the volcano lies within a tropical climate zone. At just 285 meters above sea level, Krakatau is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. The volcanic landform is characterized as a caldera, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Krakatau 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 Krakatau, 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

Krakatau has 20 recorded eruptions in the geological database, spanning from 1979 CE to 2021 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 2018 CE, reaching VEI 3 on the Volcanic Explosivity Index. With an average interval of roughly 2 years between eruptions over a span of 42 years, this is one of the more frequently active volcanoes in the database. This persistent activity suggests a robust and well-supplied magma system beneath the volcano. With eruptive activity as recently as 2021 CE, Krakatau remains an actively monitored volcano.

Significance

With a maximum recorded VEI of 3, Krakatau has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel. Its 20 recorded eruptions make it one of the most prolific volcanoes in our database, reflecting a persistent and well-documented eruptive history that has provided volcanologists with extensive data for understanding eruption patterns and forecasting future activity. Given its recent activity, Krakatau is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

— Smithsonian Institution, Global Volcanism Program