When the Mountain of Fire Blew its Top: Why the Mt. Merapi Volcano Erupted

As of this morning, the Javanese ‘Mountain of Fire,’ Mt. Merapi is still erupting. This most recent series of eruptions of one of Asia’s most active volcanoes began last month, and has been accompanied by an offshore 7.7 magnitude earthquake, and a resulting tsunami. (More on tsunamis in a future post). The combined death toll from this triple catastrophe is well into the hundreds, and many more have been left homeless.

These three disasters were all caused by the same event: the rubbing together of two of the massive tectonic plates that make up the Earth’s surface. Mt. Merapi is located at a subduction zone, a place where two plates converge, and one is forced beneath the other. In Merapi’s case, the Indo-Australian Plate is being forced beneath the Eurasian Plate. Oceanic plates always slide beneath continental plates, because the material in oceanic crust is more dense than continental material. As the oceanic plate is forced beneath the continental one it bends downward, creating a large linear groove in the Earth’s surface called an oceanic trench. These trenches are the deepest points on Earth.

Mt. Merapi sits alongside the Sunda Trench.
Mt. Merapi (A), one of the most active volcanoes in the world, sits near the Sunda Trench. This deep oceanic groove is where the Indo-Australian Plate is being subducted beneath the Eurasian Plate.

The descending plate melts as it encounters the higher temperatures and pressures beneath the surface, forming magma, or molten rock. Tectonic plates often contain water, which is released as the crust melts. The water rises through the magma, rapidly converting to steam it goes. When it reaches the crust, it bursts through, causing a violent explosion. This is what happened on October 25, when Merapi began to erupt. It is similar to what happens when you shake a soda bottle, and release the top.

As of today, 135 people have died on Merapi’s slopes, over 200 people have been injured, and almost 200,000 are refugees. Donations to aid the victims in Indonesia can be made to Direct Relief International and Doctors Without Borders.

Have you ever sen a volcano blow? Ever visited one – active or dead? Leave your thoughts in the comments below.  And if you can find it in your heart and wallet to help those harmed by nature’s fury in Indonesia, please leave me a note too – I’d love to know.

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