Saturday, October 30, 2010

Mount Merapi

Haven't posted most of the week since I've been overwhelmingly busy (half-crazed even) with work (not all of it for my job).

One of the things that happened this past week was the eruption of Mount Merapi (Gunung Merapi or "Mountain of Fire") in Indonesia.  It's one of the most active volcanoes on the island of Java so it's not particularly a surprise.

Just prior to the eruption, the government, in consultation with seismologists, raised the alert to the highest level and urged villagers living on the slopes of the volcano to evacuate.  Many did but some listened to an 83-year-old man named Maridjan - the spiritual "Keeper of Merapi."  For the past 30+ years, Maridjan appeased the volcano by tossing offerings of chickens, rice, and flowers into the crater.  I guess the spirit of Merapi was sick of chicken & rice for dinner since Maridjan and a number of his followers died for this foolishness.  When seismologists are worried about a volcano, leave.

Anyway, the initial eruption of the volcano was explosive but now seems to have settled down a little bit with lava flows seen near the summit.  This may mean that there was only a relatively small plug blocking the neck, building up gas pressure, and now released.  While the lava flows are not good for locals in the area, they are a lot better than violent pyroclastic explosions.  While there was a large earthquake (and some large aftershocks) the day before the earthquake, the two are unlikely to be related (other than the fact that Indonesia is a tectonically active place). 

What's going on there is illustrated below:

To the left would be the Indian Ocean south of the Indonesian island of Java (see map above).  The seafloor of this tectonic plate is moving toward the north at about 6 cm/yr, diving down into a seafloor trench, and sliding under Java.  As the plate subducts, frictional "stick-slip" movement causes frequent earthquakes and melting occurs at depth with magma rising up to feed volcanoes like Merapi.

As long as this plate tectonic configuration exists, Java will be subject to large earthquakes and violent volcanic eruptions.  That's the cost of living above a subduction zone  Feeding chicken and rice to volcano gods won't help.

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