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Gunung Kelud (Kelut)

What is a Lahar?
Mt. Kelud
Crater Lake
Chemical Composition
A Quick History Lesson
Cool Facts!

A lahar is essentially a mudslide, but has very complex characteristics. Keep reading for more information!

What is a Lahar?


According to the U.S Geological Survey (2000), a lahar is a term (Indonesian) used to describe a mixture of either hot or cold water and debris that flows a) down a volcano, or b) down river valleys, in the same sort of way that a mudslide would flow. They describe it as looking sort of like a mass of concrete (wet) that can carry anything from sand and pebbles to large boulders up to 10 meters in diameter.


Because the flow of lahar depends on so many things (such as speed, where it’s flowing from, and what it’s carrying), it’s nearly impossible to give it specific physical characteristics. All that’s well known is that they are definitely dangerous, especially because they are so unpredictable (U.S. Geological Survey, 2000).


Naturally, the size and speed of the lahar can be contributed to what exactly is on the slope of the volcano. Debris that is collected is often eroded, and as more and more water accumulates, the size of the lahar can easily increase more than 10 times its original size, not to mention the fact that the more water there is, the faster it’s going to move (Thouret et. al., 1998)

Figure 6: An illustration of a lahar resulting from a crater lake overflow; Source: http://www.masse

What are the Most Common Causes of Lahars?


The U.S. Geological Survey published in their 2000 report the following potential reasons for a sudden lahar:

        Snow and ice on a volcano that melts quickly

        Water ejected from a crater lake (like on Mt. Kelud)

        Intense rainfall (common during and after a volcanic eruption)

o   Mineral-rich rainwater erodes loose debris and rock on the slope, creating a landslide that saturates quickly

*These suggestions address the problems of lahars during and after eruption, and also unexplained lahars.


What are some of the Impacts of Lahars?


        Nearly everything touched by a lahar is destroyed on impact

        There is a lot of sediment deposited on the plains around volcanoes (consequently making the grounds very fertile); also adds layers of sediment to the pyroclastic/magma composition of the stratovolcano

        Entire communities can be buried

(Bourdier et. al., 1997)

by Victoria Gauthier (0330250)
Geology 1020
January 2008