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Kelud volcano
The Kelud (or Kelut) is a relatively small stratovolcano with a summit elevation at
1731m above sea level or 1650m
above the densely populated and fertile
plains of Kediri and Blitar that
surround the volcano. Kelud volcano is
located at about 27 km from the city of
Kediri (population: 1,300,000) and lies
between the volcanic massif of
Gunung Wilis to the West and the
complex of Kawi and Butak volcanoes
to the East.
Kelud volcano is considered as one of the most dangerous volcanoes of Java because
of its frequent eruptions. The eruptive activity has typically generated deadly lahars,
pyroclastic flows and surges that have claimed more than 15,000 lives since 1500 AD
and caused widespread fatalities and destruction. The crater lake of Kelud is famous
for its potential to release devastating lahars whenever an eruption occurs. The 1586
eruption produced one of the worst lahar in the historical record of volcanic eruptions
and took the lives of about 10,000 people. Extensive works to control lahars have
been achieved around the volcano. A system of drainage of the crater lake was
completed in 1926. Today, this drainage tunnel still works and maintains the volume
of the lake at a low level (2 million m3). Several dams were also built on the slopes of
this volcano in order to protect the largest towns.
Figure 2.1 Map of eastern Java. Kelud is on the west side of the N-S alignment of
Welirang-Arjuna and Kawi-Butak volcanoes.
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Geological Setting
Gunung Kelud is a composite stratovolcano built by the accumulation of numerous
lava flows (eastern and northeastern flanks) pyroclastic flows, pyroclastic surges and
lahar deposits from the youngest activity of the volcano. Debris-avalanche deposits,
several hundred meters thick underlie these deposits, and were produced by slope
failures of the western side of the volcano (Thouret et al., 1998).
Several andesitic lava domes (Sumbing, Gajah Mungkur) are present in the sommital
area, some present spectacular columnar joint structure.
Small lateral parasitic vents are also present on the flanks of the volcano; they have
erupted mostly lava flows.
The most recent eruption (1990) produced medium-K basaltic andesite pumice and
scoria with plagioclase, orthopyroxene, clinopyroxene and magnetite as phenocrysts
(Bourdier et al., 1997). Their composition (Table 2.1) is comparable to magmas
produced by the eruptive activity during the last centuries.
Eruptive activity
More than 30 eruptions have been recorded in historical times. Kelud’s 1000 AD
eruption is the oldest in the historical record of eruptions for the entire Indonesian
archipelago. Since AD 1300, the periods of inactivity between eruptions range from 9
to 75 years (Kusumadinata, 1979, Thouret al. 1998). During the past century,
eruptions occurred in 1901, 1919, 1951, 1966 and 1990. All these recent eruptions
were very similar and were characterized by a very short duration (a few hours) and a
low volume of eruptive products (0.1-0.2km3) with VEI = 3-4.
Explosive activity typically started with a phreatomagmatic outburst followed by a
short plinian eruption with convective columns reaching altitude of more than 10 km.
These eruptions produced devastating lahars, pyroclastic surges and flows as well as
ashfall deposits (see figures 2.2 and 2.3).
Figure 2.2 dispersion of ashfall deposits from the 1901 and 1919 eruptions of Kelud
volcano. Adapted from Kemmerling (1921). During the 1919 eruption, the volcanic
ash was distributed in two lobes. The low altitude ash cloud was dispersed eastward
and extended as far as Bali and the high altitude cloud dispersed to the West.
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Table 2.1: Composition of the Kelud eruption products.
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
L. I.
1
55.19
0.58
18.2
7.51
0.17
3.85
8.86
2.42
0.57
0.08
1.73
2
56.15
0.57
18.28
6.46
0.16
3.43
8.48
2.39
0.59
0.07
2.7
3
56.06
0.58
18.48
8.23
0.2
3.94
9.15
3.3
0.53
0.08
0.16
4
55.24
0.62
18.7
8.71
0.2
3.5
9.09
3.11
0.83
0.08
5
55.05
0.62
18.5
8.84
0.21
3.74
9.2
3.05
0.79
0.26
Total
99.15
99.28
100.71
100
100
<4
<4
<4
Nb
14
16
14
Rb
511
485
537
577
570
Sr
19
15
17
Y
63
64
47
Zr
<6
11
9
Pb
70
70
58
Zn
32
30
30
Co
21
25
17
Cr
159
180
135
V
522
572
539
478
479
Ba
36
42
31
Ce
1 and 2: pre-1990 eruptions, 3 and 4: 1990 pumice and 5: 1990 scoria.
1-3 from Bernard (unpublished), 4-5 from Bourdier et al. (1997).
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Figure 2.3 ashfall deposit from the 1990 eruption (Bourdier et al., 1997). This ashfall
destroyed more than 500 houses. The collapse of roofs was the main cause of
casualties (32) recorded for this eruption. (GVN Bull. 1990, Bourdier et al. 1997).
Lahars and the drainage of the crater lake
Primary lahars (or syn-eruptive lahars) are very frequent at Kelut and are produced by
the violent expulsion of the waters from the crater lake. But Kelud is also prone to
produce secondary lahars (i.e. not directly associated with an eruption) because the
volcano flanks are deeply dissected by an intense drainage system and because of the
presence of abundant, loose, pyroclastic material easily remobilized by tropical rains
during the rainy season (Thouret et al, 1998). The areas most exposed are the west
(lahar Gedok) and southwest (lahar Badak) flanks of the volcano because of the lower
elevation of the crater rim on the west side. Primary lahars were disastrous and
responsible of most of the death toll until the volume of the lake was reduced by a
drainage system.
Before 1875, the volume of lake waters reached about 78 million m3. In 1875, a
disaster not linked to any volcanic activity occurred. Heavy rains breached the crater
rim and spilled lake waters on the southwestern flank of the volcano producing a 13km long lahar that caused destruction in the Sregat and Blitar districts. After this
disaster, the volume of the lake was reduced to 40 million m3.
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Figure 2.4 paths followed by lahars during recent eruptions at Kelud volcano from
Rodolfo (1999).
Early in this century (1905), a dam was built by the local Dutch administration along
the river Badak in order to divert the lahars from the nearby town of Blitar. When the
next eruption occurred, this dam proved to be ineffective being swept away by the
lahars from the 1919 eruption. The 1919 lahars traveled in less than an hour as far as
38 kilometers and devastated an area of more than 15,000 hectares of arable land,
destroying a hundred villages and killing 5160 people. This dramatic eruption
prompted the creation in May 1919 of the Volcanological Survey of Indonesia which
decided as the first task to drain the crater lake waters of Kelud by way of a tunnel.
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The engineering work started in September 1919 and took several years to be
completed. The initial plan was to excavate a tunnel about 955m long. At the time the
work started, the crater lake was still dry and excavation of the tunnel was started
from both sides of the crater wall (Van Bemmelen, 1949). Because of high
temperatures encountered at the working front of the excavation (46°C), the tunnel
was not yet completed in 1923. At that time the crater lake was already half-full of
water (22 million m3). And a sudden flood of mud and debris invaded the tunnel
killing five workers, after which the work had to be suspended. A new plan was thus
decided to lower the lake level progressively by drilling 7 parallel tunnels and using a
siphon pipe to drain the lake waters. This extensive work was finally completed in
1926 and successfully lowered the lake to a volume less than 2 million m3. Kelud is
probably one of the first and most ambitious example of a significant engineering
work made on a volcano to reduce the threat posed by a crater lake.
Figure 2.5 Cross section of the initial tunnel works at Kelud from Verstappen (1992).
The 1951 eruption produced only minor destruction. In comparison with the 1919
catastrophe, the lahars traveled a maximum distance of 6.5 km. But, this eruption
deepened and widened the crater so that when the 1966 eruption occurred, the volume
of water in the crater lake had risen to more than 23 million m3 (Figure 2.6).
After the 1966 eruption, a new tunnel was built 45m below the lowest pre-existing
tunnel and the volume of waters was again reduced to 2.5 million m3. Several dams
and sediment traps (sand-pockets) were also built on the slope of the volcano to
reduce the dispersion of lahars.
No primary lahars were produced by the 1990 plinian eruption but at least 33 posteruption lahars occurred. They traveled as far as 24 km from the crater (Thouret et al,
1998).
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Figure 2.6 variations in the crater lake level due to volcanic eruptions and drainage
system at Kelud volcano (modified from Sudradjat, 1991).
Crater lake
Bathymetry
After the 1990 eruption, a new lake rapidly refilled the crater. The new lake is shallow
with a maximum depth of 33m. It covers an area of 95,000 m2. Bathymetric surveys
(Figure 2.7 and 2.8) show that the lake has a flat bottom. The volume is estimated at
1.9 million m3.
Figure 2.7 Bathymetric profile of Kelud crater lake obtained in August 1996. The
echo-sounder keep tracks of the bubbling of the numerous fumaroles active on the
crater floor (Bernard, 2000).
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Figure 2.8 topographic map of Kelud summit. The depth contour of the lake is in
meters; bathymetric profile of figure 2.7 is along A-B. Topographic map is from Sihat
and Djadja (1991).
Temperature
The Kelud crater lake is a hot lake. Even during periods of inactivity between
eruptions, a persistent degassing from subaqueous fumaroles maintains the lake
surface temperature several degrees above the ambient temperature (19 °C).
Monitoring of the lake temperature was very valuable as a precursor sign of the 1990
eruption. The surface temperature increased from 30 °C to 39°C during the 3 months
preceding this eruption. Together with this change in temperature, hydroacoustic
monitoring recorded an increase in the bubbling activity in the lake
(Vandemeulebrouck et al. 2000).
More recently, in 1996, the lake temperature increased from 42 to 50°C and vigorous
bubbling was observed in many places in the lake (Figure 2.7). But, despite this
strong increase in the degassing activity no eruptions occurred. Today, the lake
temperature is close to 36°C (as of May 2000). This temperature is still higher than
the average background temperature (31°C) typical of the lake during quiescent
period between eruptions.
Like many other active crater lakes, Kelud lake acts as calorimeter trapping the heat
supplied into the lake by subaqueous fumaroles and hot springs. The lake surface
radiated energy estimated at 130 MW for the period 1993-1995 when the lake
temperature was 42 °C (Figure 2.9).
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Figure 2.9 heat and mass balance model calculated for Kelud crater lake. The model
assumes that the lake is in steady state equilibrium, i.e. that the lake water temperature
is constrained by the balance between heat input and output. Heat is derived from the
enthalpy of hydrothermal fluids (brine + steam) entering and mixing within the lake
and from solar and atmospheric radiation (rad). Heat is lost by evaporation (evap),
conduction (cond), radiation (rad) and by the overflow (over) of the hot waters
through the drainage tunnel (Bernard, 2000).
The lake waters that are flowing trough the tunnel into the river Badak will not be reinjected into the hydrothermal system. The high overflow (300 kg.sec-1) combined
with the relatively small volume of this lake make the residence time of the elements
in this lake particularly short and of the order of 80 days.
Knowledge of the concentration of sulfates, chlorides or fluorides dissolved in the
lake waters as well as the water flow give estimates of the net flux for volatile
elements: Cl: 33 T.day-1, S: 6 T.day-1 and F: 0.2 T.day-1.
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Geochemistry:
The composition of the lake is rather unusual and corresponds to a near neutral
(pH∼6), relatively diluted water with a TDS of a few g.kg-1 (Table 2.2).
This neutral composition contrasts with the highly acidic waters (pH=0-3) most
frequently observed in active crater lakes where the discharge of magmatic gases
(SO2, HCl, H2S and HF) directly into the lake or into the subsurface hydrothermal
system produces acid waters with elevated concentrations of sulfates and chlorides.
This rare composition seems to be a characteristic of Kelud lake during the last 50
years, because the presence of acid waters has never been reported in the past.
Figure 2.10 shows the compositions of active crater lakes as a function of their major
anions concentrations. Most of these lakes are too acidic to convert and store CO2 gas
as bicarbonate ions (HCO3-) and they plot with variable S/Cl ratios on the SO4-Cl
axis. At the other extremity, Nyos and Monoun represent lakes where the emission of
acid gases such as SO2, H2S or HCl has now ceased. These lakes are completely
devoid of sulfates and chlorides.
Kelud lake plots in an intermediate position. Only three other examples of crater lakes
with this intermediate composition have been found so far: Quilotoa lake in Ecuador,
and the lakes of Segara Anak and Soufrière of St Vincent (Aguilera et al., 2000).
Cl
-
0
20
100
Ta
80
Sv
Ku
Kelud
40
60
Pu
Qu
60
40
Tin
Ij, P0, Ma
80
Sa
20
Pu
-SO4
100
0
Ny
Mo
Tam
20
40
60
80
100
0
HCO3-
Figure 2.10: relative concentrations of major anions in crater lakes. Qu: Quilotoa
lake, Sa: Segara Anak (Aguilera et al., 2000), Sv: Soufriere St Vincent (Sigurdsson,
1977), Ij: Kawah Ijen, Po: Poas, Ma: Maly Semiachik, Ny: Nyos and Mo: Monoun
(Delmelle and Bernard, 1999 and references therein), Pu: Kawah Putih (Sriwana et
al., 2000).
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55
55
Tem perature °C
50
50
45
45
40
40
35
35
30
30
TDS g. L -1
3
3
2
2
Cl/SO 4
1
1
Mg/Ca
0
0
1/01/94 1/01/95 1/01/96 1/01/97 1/01/98 1/01/99 1/01/00
Date
Figure 2.11: temporal evolution of temperature and geochemistry of Kelud crater lake
during the period 1993-2000 (Bernard, 2000).
The chemistry of the lake is dominated by Na and Cl that are the two most
concentrated ions, followed by SO4 and HCO3 .
A significant evolution in the surface temperature and in the geochemistry of the lake
has been observed during the period 1993-2000. The general trend for this period is
toward a lowering of the temperature of the lake (with the exception of 1996). This
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reflects a reduction in the heat supplied to the lake by the (magmatic) hydrothermal
system. During this period, the lake waters became more and more diluted (Figure
2.11). This dilution affected principally the chlorides, as well as Na, K and B that
decreased in close correlation with chlorides (figure 2.12). On the other hand, no
correlation can be observed for the variations between SO4, Ca or Mg. The
concentrations of these three elements are roughly the same today as they were seven
years ago.
In august 1996, a sudden increase in temperature of the lake was observed.
Temperatures as high as 50°C were measured and vigorous bubbling was present in
many areas of the lake suggesting an increase in the input of steam and brines into the
lakes. Changes in the lake chemistry observed during 1996-1997 could suggest the
presence of two independent systems, which are feeding the crater lake of Kelud: one
with a Na-chloride rich composition and the second with a Ca-sulfate composition.
The isotopic composition of dissolved sulfates was constant during 1993-1998. The
high values (δ34S: ∼15‰) observed suggest that the main source of dissolved sulfates
in the lake waters could be magmatic SO2.
1600
1993-94
1400
Cl mg. kg-1
1200
1000
800
600
400
2000
200
0
0
2
4
6
8
10
12
14
16
B mg.kg-1
1600
1993-94
1400
Cl mg. kg-1
1200
1000
800
600
2000
400
200
0
0
200
400
600
800
1000
1200
Na mg. kg-1
Figure 2.12: evolution of chloride vs boron and Na in the Kelud lake waters.
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Cultural information
An important Hindu kingdom was established in 1049 in the plain, along the Brantas
river, west of the volcano: the kingdom of Kediri. From the 11th to the early 13th
century, Kediri was the most powerful kingdom of the entire Indonesian archipelago.
This kingdom was renowned for its naval and commercial strength and for its
achievements in literature. It collected spices from tribes in southern Kalimantan
(Borneo) and the Maluku Islands, famed in the West as the Spice Islands or Moluccas.
Muslim traders visited its ports from India as well as Chinese merchants.
Many Hindu and Buddhist temples have been found in this area. Eleven temples have
been identified so far dating back to the 9th and 15th centuries. Candi Penataran is the
largest and most important Hindu temple complex in East Java. It lies just 10
kilometers north of Blitar on the lower slopes of Mt Kelud (Figure 2.1). Dedicated to
the god Shiva, the temple was in use for at least 300 years, from the 14th to 16th
centuries.
Today, agriculture is the major economical activity. The fertile plains at the foot of
Gunung Kelud produce rice, sugarcane, pineapple, cotton, cassava, corn, peanuts,
coconuts, soybeans, coffee, cocoa, quinine, tobacco and indigo.
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