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Gunung Kelud (Kelut)

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

The fact that Gunung Kelud is characterized particularly by its deadly crater lake definitely gives credit to this page!

What is a Crater Lake?


A crater lake is sort of like a build-up of water at the summit of the volcano. Essentially, there is a depression (like a basin) at the summit, very similar to the holes we see on the surface of the moon. The water that builds up in the crater is usually magmatic vapour that has been condensed (Kusakabe, 1994).


Why are Crater Lakes so Dangerous?


Crater lakes are a hazard all their own. Aside from the fact that they generally cause catastrophic mudslides when the volcano releases pressure during an eruption, but the same study by Kusakabe (1994) suggests that the crater lakes themselves have the potential to erupt. Evidently what happens is that CO2 that gets released with the expulsion of magma can get trapped in the bottom layer of the lake and accumulates. Eventually, the gases build so much pressure that they really have to go somewhere!


To further reinforce the fact that crater lakes are a very important geological phenomenon, there is even an organization dedicated solely to the study of them: the IWGCL (no, not the International Working Group on Child Labour, the OTHER IWGCL—the International Working Group on CRATER LAKES! haha) Kusakabe (2004), notes that they are dedicated to “proposals on ways to prevent future gas disasters, results of search for gas accumulation in other crater lakes, geochemical monitoring of active, hot crater lakes, fluid-volcano interaction in terms of chemical and isotopic variations, and an evaluation of past volcanic activity recorded in sediment cores from volcanic lakes,” (p. 137).


The Chemical Composition of a Crater Lake


According to Bernard (2000), most crater lakes are quite acidic in composition. In fact, they are characterized by gases like SO2, HCl, H2S and HF, which are usually discharged directly into the water. He also suggests that the hydrothermal system that heats up a crater lake produces very high concentrations of sulfates and chlorides in the water, essentially producing acid water.


 Mt. Kelud’s Crater Lake


As though the phenomenon of the crater lake wasn’t important enough, Mt. Kelud had to go and complicate things! Its hot lake is uncharacteristically neutral in composition. In fact, Kelud’s waters are more similar to that of diluted water than most crater lakes (Bernard, 2000)! This isn’t just a fluke either, because acid water hasn’t been reported in the past 50 years, meaning that its very unusual composition is really just another of its characteristics.


One thing that’s important to know about crater lakes is that they aren’t just there and they definitely don’t occur overnight! In fact, Mt. Kelud’s crater lake has been one of Mother Nature’s works in progress since the day Kelud appeared on the Earth’s landscape! However, volcanologists have been paying particular attention since 1923! The image below shows the recorded changes in Gunung Kelud’s crater lake since 1923.


Figure 4; Source: Bernard, 2000.

Solutions to Mt. Kelud’s Crater Lake Problem


In 1967, a tunnel was completed that ran from the crater lake to the outside of Kelud’s dome, in an attempt to drain some of the water from the hot lake. This proved to be a temporary solution, however, every time there is an eruption, the lake fills up again. After an eruption in 1990, a lake quickly filled the larger than ever crater, a volume estimated at 1.9 million meters cubed (Bernard, 2000). That’s alot of hot water!


Quick Facts about Mt. Kelud’s Crater Lake


Gunung Kelud’s Crater Lake

(all facts courtesy of Bernard, 2000)


        During periods of inactivity, the average temperature of the lake was 19⁰C.

        Prior to the 1990 eruption, the lake increased from 30⁰C to 39⁰C in just 3 months.

        In 1996, while there was no eruption, the temperature increased from 42⁰C to 50⁰C.

        As of May 2000, when this study was done, the temperature of the lake was 36⁰C.


        Mt. Kelud’s crater lake has a maximum depth of 33 meters.


        The lake is covers approximately 95,000 square meters.


        The lake, as mentioned above, is estimated to be 1.9 million meters cubed.

by Victoria Gauthier (0330250)
Geology 1020
January 2008