The Ingredients for a Lahar

[Viva_La_Revolution]

Colima lahar videos
Posted on December 27, 2011 by John A. Stevenson

The Indonesian word, lahar, is the technical term used to describe volcanic mud flows. This post explains the difference between two types of lahars (hyperconcentrated flows and debris flows), using videos that I recorded at Volcán de Colima as examples.

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The summer of 2005 was the most active period at Volcán de Colima in nearly 100 years. Hundreds of explosions blasted from the crater; the largest produced pyroclastic density currents that dumped millions of cubic metres of smashed-up volcanic rocks upon the upper slopes and within the ravines (barrancas) on the flanks. Uncemented by clays, the deposits are a loose, rubbly mixture of boulders, cobbles, gravels and sandy and dusty ash.

Fast-forward to summer 2007, and the middle of the rainy season. Sweaty, humid nights dawn into blazing sunlit mornings, but clouds soon form. By 12.00hrs the summit of the volcano is lost and thunder begins to rumble. Mid-afternoon, every day, the tropical rain hammers down. And I mean hammers; rainfall of 100 mm in 3 hours is not uncommon. By contrast, London gets 750 mm in an entire year.

The first video shows what this kind of rain looks like. I had gone with Flo, a volunteer at the Universidad de Colima, to maintain a radar monitoring station on the south flank of the volcano, about 3 km from the crater. (Click here for a Google Earth file that shows the monitoring station and the debris-covered flanks of the volcano). We had barely started our work when the rain arrived, so we had to sit it out in order to finish what we needed to do.

http://all-geo.org/volcan01010/2011/12/colima-lahar-videos/

[Igel]

1. Javanese.

For many in Java it's like saying that "chocolate" is originally a Spanish word.

Nahuatl advocates would pitch a fit at the very idea of attributing a Nahuatl word to their Spanish colonizers and oppressors.

Same with describing a Javanese word as "Indonesian." (We probably got "lahar" straight from Javanese, unlike "chocolate", which we didn't get directly from either Nahuatl or Spanish.)