The Kelut is a
volcano located on the main
island of
Indonesia,
Java. It is a relatively small
stratovolcano, its
summit elevation being only 1,731 meters, but it packs a deadly punch due to the summit
crater lake it contains. It has been the source of some of Indonesia's most
deadly eruptions, one of the most memorable being the
eruption of 1919, which killed more that 5,000 people. These
deaths were mostly due to the
pyroclastic flows and
lahars resulting from the eruption.
Large eruptions
The eruption of 1586 also caused a huge number of deaths, some
reports say more than 10,000. This eruption
ejected more than 1
cubic kilometer of
tephra, which gives an indication of its size. For
comparison: the
Pinatubo (
Philippines) eruption of 1991 had an tephra ejection
volume of about 10 cubic
km, the
Mt. St. Helens (
USA) eruption of 1980 had a volume of about 1.5 cubic km, and the
Krakatau1 (Indonesia) ejected more than 18 cubic km of tephra in its 1883 eruption.
As an aside, the Krakatau is generally the most well known
big eruption in
recent history (
geologically speaking), but the 1815 eruption of the
Tambora, which forms the Sanggar
peninsula of
Sumbawa Island in Indonesia, is the largest in both number of deaths and ejected tephra. The eruption blew 150
cubic km of tephra volume into the
sky, and killed an estimated 92,000 people, 10,000 of which were direct
fatalities caused by tephra fallout and
pyroclastic flows, and the remaining 82,000 due to
starvation and
disease following the
event. In contrast, the estimated Krakatau
tally was no more that 36,500 dead, mostly due to the resulting
tsunamis.
The most recent
rumblings of the Kelut were in 1990, when it erupted
explosively (with an
Volcanic Explosivity Index or
VEI of 4). An estimated 32 people died. This low number of deaths was mainly due to tens of thousands of people being
evacuated beforehand. Pyroclastic flows reached up to 8 km away from the volcano and fist-sized tephra fell up to 55 km southwest of the volcano. Subsequent lahars buried agricultural land under a layer of
mud and
debris.
Curbing the crater lake
After the eruption of the Kelut in 1919 it was recognized that something had to be done to minimize the
risks posed by the crater lake. Ejection of
water during eruptions caused lahars that wreaked
death and
destruction around the mountain. In 1926
construction of
drainage tunnels was started to lower the
level of the lake. This first
project resulted in a lowering of the lake level by more than 50 meters.
In 1951 another eruption deepened the
crater by 70 meters, rendering the
tunnels ineffective in reducing the water volume of the crater lake. After
repair of the tunnels an estimated 50 million
cubic meters of water remained in the lake, which resulted in an increased death toll of 200 when the volcano
erupted again in 1966. A new deeper
tunnel system was constructed so that the volume of water in the lake
prior to the 1990 eruption was only about 1 million cubic meters.
On January 19, 2001, the
Volcanological Survey of Indonesia raised Kelut's
Alert Level from 1 to 2 (on a
scale of 1 to 4). During the first months of 2001 the
temperature of the lake increased from 38.5°
Celsius to about 51° in the first week of February, after which it dropped back to around 48°.
Simultaneously the
acidity of the water increased, the
pH dropping from 6.3 to 5.3. At the moment (July 26, 2001) the Alert Level remains at 2.
No more crater lake?
It seems that during 2008 a
lava plug has developed at the bottom of the crater lake, boiling off most of the water. At the moment it has completely filled out the old crater lake and has actually covered up the intake of the water tunnel.
Swimming in the crater lake
I once had the rather
strange (and at the time scary) experience of swimming in the crater lake of the Kelut. My family and I were visiting friends that lived near
Malang, which is not far from the Kelut, so we decided to drive out to it, hike up its
slope and down into the
caldera and have a
swim in the lake. It should have been rather
fun, but I had just seen a teen
horror movie which featured a rather
murky lake, missing persons and a lake monster (that turned out to be some digging rig - it was a long time ago), so I was rather
apprehensive of swimming in this rather
opaque, blue-green water. The thick
crusts of
moss or
algae that were loosened and
floated up by touching the
slippery bottom didn't help much, either. However, after some initial
wariness I had quite a nice time of it. The water was nice and
warm, not too
hot and I remember it tasted strange.
One other thing I remember from that hike to the lake is that my father was telling me how his father had somehow been involved in building or maintaining the original tunnels that were built after the 1919
explosion. I'll ask him again sometime what it was exactly so I can update this in the future.
Sources:
http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/indonesia/kelut.html
http://nmnhgoph.si.edu/gvp/volcano/region06/java/kelut/var.htm
http://www.ddj.com/articles/2001/0103/0103f/0103ff5.htm - a picture of the interior of the caldera
http://www.doubledeckerpress.com/kelut.htm - and another picture
http://volcano.und.nodak.edu/vwdocs/eruption_scale.html - information on VEI
http://users.bendnet.com/bjensen/volcano/largerup.html - info on large eruptions
http://www.geo.arizona.edu/geo2xx/geo218/UNIT3/lecture11.html - more on large eruptions, including estimated death tolls
1 Some would insist on calling it Krakatoa
July 26, 2001