Tuesday, November 28, 2017

Eruption of Mount Agung

Mount Agung, 9944 feet, is in western Bali.  One of 78 active volcanoes in Indonesia, its last major eruption occurred in 1963 but another is expected within the next few weeks.  Earthquakes developed on and near the volcano back in September and the release of smoke and ash has been intermittent throughout October and November.

The volcanic islands along the western and southern edge of Indonesia have formed as the Indo-Australian Plate has been subducting beneath a southeastern extension of the Eurasian Plate.  As it is forced downward, toward the Earth's mantle, the leading edge of the subducting plate melts and plumes of magma push up through the crust of the overriding plate.  Initially producing a volcanic island arc, the ongoing subduction and volcanism has culminated in the large islands that we observe today (Sumatra, Java, Bali and others to their east).

Another major eruption of Mount Agung will likely produce widespread devastation but will not come close to the effects of Mount Toba's eruption, on Sumatra.  That supervolcanic eruption, which occurred 74,000 years ago, temporarily cooled the Earth's climate and had a major impact on the human population of our planet; indeed, a significant percentage of early humans had left Africa and colonized the southern rim of Asia by that time (see The Toba Winter).