Growing lava dome observed in the lake of Kelud volcano, Indonesia.

Last update February 5, 2008

 

9nov_swir
The new lava dome growing in the middle of Kelud's lake can be seen from space thanks to ASTER satellite. This is a SWIR image (1.6 - 2.4µm) with a resolution of 60 meters/pixel.. A steam plume is visible on the left side of the dome (yellow pixels). ASTER image courtesy of NASA, USA.

 

flir
Thermal images recorded with a FLIR ThermaCam P25 on November 9 by A. Solikhin and Segy (CVGHM). Courtesy of Volcanological Survey of Indonesia. "Kubah" means dome in bahasia indonesia.

 

6122007
The "Anak Kelud" as of December 6, 2007. © CVGHM, Indonesia.

 

26jan08

January 26, 2008. The inlet of the drainage tunnel previously used to control the volume of lake waters is now covered by the lava dome. © CVGHM, Indonesia.

 

 

The Kelud

 

javamap

Kelud (or Kelut) is one of the most active and hazardous volcanoes of Indonesia with a record of 29 eruptions which have claimed more than 15,000 lives since 1500 AD. The volcano lies above the fertile plains of Kediri and Blitar and is a threat for more than 1 million people living in this densely populated area of Java .

After the last eruption that occurred in February 1990, a new lake rapidly filled the crater of this volcano. The lake is shallow with a maximum depth of 34 m and a volume of 2.1 million m3. A tunnel was drilled through the crater wall in 1926 to drain the lake and keep its volume constant. The composition of the lake is rather unusual for an active volcano and corresponds to a near-neutral pH (6-7) relatively diluted water with a TDS of a few g.kg-1. Persistent degassing from subaqueous fumaroles and hot springs discharging into the lake maintain water temperatures between 28-42°C, largely above the ambient temperature of 19°C. This hot lake can be regarded as the subaerial part of an underground heated aquifer or hydrothermal system ( Bernard and Mazot, 2004).

 

Signs of unrest:

 

 

In the framework of a cooperation agreement between Indonesia and Belgium, a field work carried by a joint team of CVGHM (Center for Volcanology and Geohazards Mitigation) and two belgian universities ULB and FUNDP discovered an intense degassing of the lake floor in early July 2007. The echo soundings recorded at that time revealed that almost 70% of the lake floor was degassing (see the echograms and CO2 flux map below).

The data from the echosoundings were confirmed by direct measurements of CO2 from the lake surface. Total flux was estimated at 330Tons/day which corresponds to a tenfold increase compared to 2006 (35Tons/day). The CO2 flux was again measured in early September by CVGHM staff and reached 730Tons/day.

Lake temperature measured at depth (15 meters) in the middle of the lake is increasing continuously since August 8 as well as the conductivity of the lake waters.

The colour of the lake waters changed rapidly in August and September from the typical green to yellow and bluish. See the bottom of this page.

 

map1
Monitoring instrumentation inside the lake. (1) Temperature and conductivity of the lake at 15m depth + Meteo station: air temperature and humidity, wind velocity and direction. (2-4) lake level sensors, the difference in lake level between 3 and 4 is used as tiltmeter. (5) radon sensor.

 

map2
Outlet tunnel is a pressure sensor to record the flow of lake waters trough the drainage tunnel (about 960m long).

 

1. Echosounder data

 

echo1
Echosounder profile recorded with a Simrad ES60 dual beam (50 and 200kHz) in July 2007. The vertical tracks are columns of CO2 bubbles rising to the surface. The colour scale reflects the variable intensities of the backscattering of the sound wave by the gas bubbles, roughly proportional to bubble concentrations. Whenever the concentration of bubbles is high , the echosounder has trouble to clearly detect the bottom.

 

lochness
Another area of the lake with intense degassing. Lake bottom is here close to 32 meters. The two "eyes of the monster" are supposed to be large CO2 bubbles rising fast to the surface. Bottom fumaroles frequently show discontinuous degassing (puffing). 200kHz echogram processed with Echoview software.

 

Sv
Map obtained from 16 different echosounder profiles (50kHz data) covering the all lake. Sv is the mean backscattering strength of the water column, (db) are decibels. The zone of maximum degassing is correlated with thermal anomalies of the lake floor measured in 2004 (see next figure). Echosounder data processed with Sonar 5 software.

 

suhudibawa
Temperature of the lake floor measured in August 2004. The white + are the measuring spots. Maximum temperature was 106°C.

 

 

2. CO2 flux data from the lake's surface.

 

 

chamber acu
The flux of carbon dioxide is measured with an accumulation chamber. At left, the chamber floating on the lake in July 2006. The silicon tubing is connected to a IR spectrometer (inside the Bombard). At right, a typical CO2 accumulation curve obtained in 2007.

 

codua
Map of the flux of carbon dioxide in grams per square meter per day obtained from 230 spots measurements with the floating accumulation chamber between July 30 and August 2, 2007.

 

CO2flux
In blue, the evolution of the total CO2 flux (normalized to the lake area :103,600m2) since 2001.

 

 

3. Lake temperature and conductivity:

 

Graph Page 10

Evolution of lake temperature since July 2006. The temperatures (measured at a depth of 15 m) show a clear increase since August 8, 2007. Last update September 29, 2007.

oct8
Lake waters last temperature update (October 8, 2007) showing the steady warming of the lake. Access to the buoy was not authorized by local authorities.

 

cud_cond
Evolution of the conductivity of the lake waters. This increase in conductivity reflects the change in the chemistry of the lake waters (i.e. the concentrations of ions in solution are increasing). The increasing trend observed during the summer 2006 is principally a seasonal effect (dry season and evaporation of the lake). The rainy season started on November 6 and progressively diluted the lake-hydrothermal system. The current trend of increasing conductivity can not be explained solely by evaporation and dry season effect.

 

4. Changes in the color of lake waters:

 

15aug 31aug
6sept
Views of the successive changes in the color of the lake waters. Photographs courtesy of Akhmad Solikhin and Khirul Huda (CVGHM).

 

5. Flow trough the drainage tunnel:

 

outlet2
High overflows through the drainage tunnel (150-500l.s-1) are typically observed even during the dry season (from June to October) and suggest that the recharge of the lake is mainly by the hydrothermal system. C peak is the result of a cleaning operation of the drainage tunnel this summer. Last data: October 8, 2007.
tunnel

 

 

 

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Université Libre de Bruxelles. Last modification: February 5, 2008

Webmaster: A. Bernard

 

 

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