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.
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
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.