The eruption of Mount Agung on the island of Bali has sparked worldwide media interest, yet volcanic eruptions in Indonesia are nothing new. Of the country’s 139 “active” volcanoes, 18 currently have raised alert levels, signifying higher than normal seismic activity, ground deformation or gas emissions. On a global scale, in any week in 2017, there were at least between 14 and 27 volcanoes erupting.
Most observed volcanic activity takes place along the Pacific Ring of Fire, a region around the Pacific Ocean where several tectonic plates meet, causing earthquakes and a chain of what geologists call subduction zone volcanoes. Other eruptions occur at volcanoes within continental interiors such as Ol Doinyo Lengai in Tanzania, or on oceanic islands like Hawaii. Many also take place hidden from view on the sea floor, with some of the most active underwater volcanoes located in the Tonga-Kermadec island arc in the south-west Pacific.