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8/11/2019 ERUPTIVE HISTORY OF THE DIENG MOUNTAINS REGION, CENTRAL JAVA, AND POTENTIAL HAZARDS FROM FUTURE
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EVALUATION OF INITIAL INVESTIGATIONS
DIENG GEOTHERMAL
AREA,
CENTRAL
JAVA, INDONESIA
by
L . J . P .
Muffler
U . S .
Geological
Survey
U * S . Geological
S u r v e
OPEN TILE REPORT
T h i s r e p o r t i s preliminary and
has
n o t been e d i t e d o r reviewed f o r .
o o a f
onaity vith G e o l o g i c a l Survey
s t a n d a r d s o r n o m e n c l a t u r e *
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CONTENTS
Page
Summary and recommendations 1
Introduction
1
Evaluation procedure
2
Summary
a n d
analysis
of
initial investigations
3
Electrical geophysical survey 3
Dipole survey 4
Modified
Schlumberger profile 6
Schlumberger sound ings
6
Audio-magneto-telluric measurements
7
Geochemical survey
7
Geologic
interpretation
10
Recommendations
12
Objectives and
requirements
o f
drilling
14
V olc a n i c, earthquake, a n d l a n d s l i d e
h azar d s 1 7
Organization
o f t h e
exploratory program
18
Supporting geological and geophysical investigations 19
References cited 20
Illustration
Figure 1 . To p o g ra p h i c m a p
at
1:25,000
o f
Dieng-Batur area (20-meter
contour interval. Shows dipole surveys made
from
source
A
a n d
source
B
o f Jacobson, Pritchard, a n d Keller ( 1 9 7 0 ) . Also
s h o w s
drill sites recommended
by
Muffler
a n d t h e
other
members
o f t h e
evaluation
team
f o r
200-meter
exploratory
h o l e s . Sites are numbered in order
o f
decreasing
priority. j n
pock
Table
Table
1
Hist o ri c
phreatic
eruptions a n d hydrothennal explosions
i n t h e Dieng'Mountains.
1 7 a
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SUMMARY AND
RECOMMENDATIONS
Evaluation o f
t h e geophysical,
geochemical,
a n d
geological
studies
carried
o u t i n
1970 i n
t h e
Dieng
Mountains has
been completed.
On the
basis of
t h e e v a l u a t i o n ,
i t
i s
recommended
that
exploratory drilling
of t h e Dieng
geothermal field be
undertaken following
t h e
general
program
outlined
by
Muffler ( 1 9 7 0 ) .
I t
i s recommended that
s i x
explorato ry holes be
drilled,
each
to a dep th
o f approximately
200
m . Proposed sites
a r e :
1 .
Pagerkandang Crater
2 .
Just west o f
Telaga Terus
3 . Just
north
o f
Pawuhan
4 . 3 / 4 km east o f Sekunang
5 . Just
southeast o f
Sidolok
6 .
J u s t west o f
Dieng
Wetan
After completion
o f t h e
2 0 0
m holes,
t w o
holes should
be
drilled t o
a
dep th o f approximately 650
m .
INTRODUCTION
Interest in possible utilization
o f
the geothermal resources o f the
Dieng
Mountains
dates back t o 1 9 2 8 , w h e n the Dienst
Van Den
Mijbouw drilled
several exploratory h o l e s , t h e
deepest
t o 80 m (Purbo-Hadiwidjojo, 1968;
Hoesni, Arismunandar, a n d
R a d j a ,
1 9 7 1 ) .
Although
temperatures up
t o
145C
were f o u n d ,
t h e r e was n o
follow
up t o this limited
exploratory drilling.
Renewed interest
i n
t h e area
was
stimulated by
t h e
UNESCO Volcanological
Mission ( T a z i e f f , Marinelli, and Gorshkov,
1 9 6 6 ) ,
and was furthered by a
geothermal
mission
sponsored
by
t h e
French
government
i n
1 9 6 8 .
Both
missions recommended further investigations
a n d
development
o f t h e
geother
resources
o f t h e
Dieng
a r e a .
At the request o f
t h e
Indonesian
government
and under t h e auspices of t h e
United States Agency
f o r
International Development ( U S A I D ) ,
a
report
recommending
s t e p s t o evaluate an d
( i f
warranted) t o
develop
t h e
geotherma
potential o f t h e Dieng
Mountains was
prepared by t h e United States
Geological
S u r v e y ( M u f f l e r ,
1 9 7 0 ) . This
report
was based on
a
study of
t h
available literature a n d a brief
visit
to t h e Dieng Mountai ns. The report
concluded
t h a t t h e
Dieng probably contained significant reserves of
geothermal
e n e r g y , a n d
recommended
a three s t e p
program
with
initiation
o f
each
successive s t e p t o be
conditional upon
favorable indications
from
t h e
preceeding s t e p . Recommended steps were:
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The alms
o f
s t e p s
1
a n d 2 were t o determine:
a )
whether the fumaroles are
Indeed t h e surface
manifestations
o f a
l a r g e , deep geothermal
system, b )
the optimum siting o f exploration a n d development wells, c )
the
size of
t h e geothermal
s y s t e m , a n d
d )
t h e
characteristics
of t h e
reservoir ( d r y
steam v s hot
w a t e r ;
acid v s
neutral; temperature;
transmissibility;
e t c . ) .
Geophysical, geological,
and
geochemical investigations recommended
as
s t e p 1
i n
t h e
USGS repor t
were carried o u t
during
t h e dry season
of 1970
as f o l l o w s :
a .
An electrical
geophysical
survey was conducted
by Group
Seven
I n c . ( J a c o b s o n a n d
Pritchard,
1 9 7 0 ; Jacobson,
Pritchard,
and Keller, 1970)
under
contract with USAID with strong counterpart support from t h e
Geological Survey o f Indonesia
( G S I )
a n d
t h e
Power Research Institute
( P R I ) .
b . Fumaroles, hot springs, a n d rivers o f t h e Dieng Mountains a n d
surrounding areas were sampled
a n d
chemically analysed
by
t h e
USGS and
t h e
G S I .
The
data are
summarized
and interpreted in
a preliminary geochemistry
report ( T r u e s d e l l ,
1 9 7 0 )
and in
a
final geochemistry report ( T r u e s d e l l , 1971)
c . Excellent
aerial photographs
of t h e
Dieng
Mountains an d
surrounding
terrain were provided by Geotronics
( p r o c e s s e d
by
P . N .
Aerial
Surveys)
un der
contract t o U S A I D .
d .
Using these photographs, a photogeologic map o f the Dieng area
was prepared by t h e GSI ( P a r d y a n t o ,
1 9 7 0 ) .
Additionally, four topographic maps at 1:5,000
scale
of about
2 1
km^
of the
Dieng
a n d Batur areas were
prepared from
surveying
data by
t h e
Indonesian
Power Research Institute ( P R I ) . Contour
interval
i s
5
meters.
EVALUATION PROCEDURE
The results o f
t h e
initial investigations have been reviewed and evaluated
by
a
team
composed o f
the following
persons:
?
L . J . P . Muffler, Geologist, USGS, Chairman
Djajadi
Hadikusumo, C h i e f ,
Volcanological
S u r v e y , GSI
H . L . O n g , Lecturer, Institute
Technology
of
Bandung
( I T B )
Vincent
R a d j a ,
Chief
o f
Operation, Electric Power Survey
Project, PRI
M . T . Z e n , Senior Lecturer, ITB
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The evaluation t eam had
t h e
following
g o a l s :
1 . T o review and evaluate t h e initial investigations completed in
1 9 7 0 .
2 . T o
recommend
whether
o r
n ot t o proceed w i t h
exploratory
d r i l l i n g .
3 .
I f exploratory drilling was recommended, t o indicate
t h e n u m b e r ,
approximate
location, and
depth
o f holes
required
to
adequately
assess
t h e
potential
o f t h e
geothermal
s y s t e m .
The
evaluation
team
( e x c l u d i n g
O n g )
visited
t h e
Dieng
Mountains on January
1 4 an d 1 5 , 1 9 7 1 , with M . R . KLepper ( U S G S ) , D . D .
Fowler
( U S A I D ) ,
Sutardono
( P R I ) , an d
I
Sjamsu ( P R I ) . Blessed by
relativel y dry
weather,
the group evaluated
t h e
thermal features
and
their geologic
s e t t i n g ,
inspected possible drilling
sites and
considered
problems o f
road
access,
site
preparation, and
sources of
drilling
water.
Evaluation
o f t h e initial investigations
was carried
o u t a t t h e GSI in
Bandung
o n
January
18-21 a n d a t
USAID
in
Djakarta January
2 2 . A
preliminary
evaluation
r e p o r t ,
dated January 2 2 ,
1 9 7 1 ,
was written by Muffler , with
the
counsel
and
assistance
o f the
other members of
t h e
evaluation team
and
w i t h
the invaluable assistance o f M .
R . K l e p p e r .
The final evaluation
report was prepared by Muffler
a t t h e
USGS
i n Menlo Park, California,
February
1 - 1 0 , 1 9 7 1 , and supersedes t h e
preliminary
report.
SUMMARY AND
ANALYSIS OF INITIAL
INVESTIGATIONS
E lec tri c a l
Geop hys ical
Surv ey
An electrical
geophysical survey
using
several techniques was conducted
i n
t h e Dieng
Mountains
in
July a n d August, 1970
by
Group
S e v e n ,
I n c . under
contr act AID/ea-123. Assistance and location surveying
were
provided
b y
G S I .
Results of
t h e
electrical
survey
are contained
in
a preliminary
report dated August 2 7 ,
1970 ( J a c o b s o n
and Pritchard,
1 9 7 0 )
and
in a
final
report dated November 1 , 1970 ( J a c o b s o n , Pritchard, an d
Keller,
1 9 7 0 ) . At
the
request
of USAID, Group Seven
subsequently prepa red
a revised Plate I
showing metric coordinates.
These reports contain
useful
data
a n d
interpretative
information, and
are
valuable aids
in
evaluating
t h e
geothermal potential
o f t h e
Dieng Mountain s
a n d
i n
recommending
sites for exploration drill h o l e s . Efficient use of
t h e reports, however,
i s
impaired by several
deficiencies
i n
coverage
and
in
format
of
data
presentation:
1 .
The dipole survey did not extend sufficiently far
o u t
from
t h e
low resistivity
anomalies t o give
a
reliable indication
o f
background
resistivity values i n non-thermal
g r o u n d .
A dipole source near B a t u r ,
f o r
example,
would have been very
useful.
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2 . Both dipole sources
were
sited in thermal
ground,
whereas at
least one s h o u l d
have been
sited in
non-thermal
ground, as
outlined by
prelimi nary Schlumberger
s u r v e y s .
>
r i i %
i
^ * v
I . 7
3 .
Additional Schlumberger profiling would have been useful,
particularly along
the roads t h a t connect
K awah
Sikidang w i t h
the Dieng-
Batur r o a d . 1 /
4 . The
maps
accompanying
t h e final
report are very difficult t o
use,
primarily because
o f
inadequate geographical
control.
The three
plates
accompanying
the final report show no coordinates, bench marks,
or
triangulation
points, and t h e DIeng-Batur road i s s o generalized that i t
i s difficult t o use
as a r e f e r e n c e .
These deficiencies occurred despite
the availability
o f
published topographic
maps.
Also, Plate
I I
for
some
inexplicable reason was
drafted with north t o t h e bottom.
5 .
There
are several discrepancies between illustrations. For
example,
figure
2
of
t h e final
report
i s
misleading,
i n t h a t there
should
be
a
gap
of
2-1/2
km
between locations
3 and 4 ( c f .
figure
1 of the
final
report
a n d
figure
5 o f
the preliminary
report).
6 . The tables accompanying
t h e
final report are very difficult t o
use
because there
i s n o
explanation
of the
tabular
format, a n d
because
the
column
headings
o f
table 2 are incompletely
l a b e l e d .
Three electrical techniques were used by
the
Group Seven field
p a r t y :
dipole
s u r v e y ,
modifie d Schlumberger profiling,
a n d
Schlumberger
s o u n d i n g s .
In
addition, t w o audio-magneto-telluric traverses
were made, as
well
a s
o n e electromagnetic
s o u n d i n g .
Dipole Survey
The dipole
results
are
presented by Jacobson, Fritchard, and
Keller
( 1 9 7 0 )
a s t w o
apparent resistivity
maps ( P l a t e s
I
and I I )
contoured
in ohm-meters.
One map
gives results
from
a
source dipole
located south
o f Dieng
Rulon
(Source A ) , a n d t h e other
gives results from
a
source northwest o f Karangengah
( S o u r c e B ) . These maps have been redrafted at
1:25,000
and
are
shown on figure
1 o f
this
r e p o r t .
Resistivity
varies
inversely w i t h temperature, salinity,
* /
There are significant discrepancies between the topographic map
( b a s e d on the published 1:50,000 Batur
s h e e t )
and the sketchy base m aps
used for Plates I and
I I o f
Jacobson, Fritchard
a n d
Keller
( 1 9 7 0 ) .
The
discrepancies are particularly
bad
in the vicinity
of
dipole source B
a n d
could not
be
satisfactorily resolved
on figure
1 o f this
r e p o r t .
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The
boundary
of the
geothermal
system c a n n o t be
defined precisely
from t h e
resistivity
data,
for data points outside
t h e
anomalous area are insufficient
t o reliably determine t h e apparent resistivity of
t h e
non-thermal volcanic
r o c k s .
T h e
5 ohm-meter contour chosen
b y Jacobson,
Pritchard, and Keller
( 1 9 7 0 )
i s
a reasonable g u e s s ,
b u t
there
i s
n o a
priori
reason
why
t h e
boundary
o f t h e
system
should
correspond
t o t h i s
particular
contour.
The
absolute
value
o f
resistivity within
a geothermal system i s a
complex
function
o f
temperature,
salinity, porosity, a n d
clay and zeolite mineral
c o n t e n t , a n d t h e
aggregate
effect these factors
have
on
resistivity varies
from one geothermal system t o
a n o t h e r ,
depending
on
t h e
relative importance
o f t h e f a c t o r s .
T h e s e c o n d
area
o f
low resistivity,
a t
Tjandradimuka, i s incompletely
defined,
b u t
appears t o have
an
extent
o f at
least 1 k m ^ . The dipole data
indicate t h a t
there
i s
no
apparent connection
between
t h e
Tjandradimuka
geothermal
system
and t h e much larger Dieng geothermal
s y s t e m ,
a t least at
depths shallower than several k i l o m e t e r s .
Modified Schlumberger profile
A resistivity profile along
t h e road
from
Dieng
Kulon
t o
Batur
was
constructed from
modified
Schlumberger arrays about five source
array
l o c a t i o n s .
The resistivity
contrast on t h e
profile
i s good, and t w o
areas
o f low resistivity are defined ( j u s t
west of
Dieng Kulon
and t o t h e
northwest o f Karantengah). These zones o f low resistivity were emphasized
in t h e
prelimin ary Group Seven
r e p o r t , b u t
deprecated
in t h e
final
r e p o r t .
There
seems t o
be n o good reason
for
t h i s downgrading
o f t h e
data, and
the
anomalies shown on
figure
5
o f
Jacobson
a n d
Pritchard ( 1 9 7 0 ) and which
can
easily be contoured
o n
figure
2
o f
Jacobson, Pritchard, and Keller
( 1 9 7 0 )
appear t o be valid. I t should
be
noted t h a t dipole survey A shows
a
lobe
o f resistivity less than 10 ohm-meters covering
t h e
area northwest of
Karantengah.
No resistivity low
i s shown
on Plate
I I ,
but
t h e
data near
s o u r c e
dipole
B i s
suspect
f o r t h e s a m e reasons t h a t
applied
t o source
dipole
A (discussed a b o v e ) .
Schlumberger sound ings
F o u r
Schlumberger soundings
t o spacings
( A B / 2 )
o f 2 0 0
meters were made over
areas t h a t showed
very
low
resistivity
i n
the
dipole
s u r v e y . These
show
t h a t
ground
o f
very
low
resistivity
a t
Kawah Sikidang
a n d
Kawah Sileri
fumaroles extends downward
t o
at least a depth
o f
approximately 200
m .
A
sounding
within Pagerkandang
crater s h o w e d that
resistive rock overlies
material o f
low resistivity
t h a t c a n readily be interpreted
a s
h o t .
The
fourth sounding, on the south
rim
o f Pagerkandang c r a t e r , probably
i s n o t
meaningful owing t o steep
t o p o g r a p h y .
At
m o s t ,
i t reflects
t h e
highly
resistive rock expected
i n a ridge 1 0 0 m above t h e
bottom
o f
Pagerkandang
c r a t e r .
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m easurem en t s ( A M I )
travers es
were
made: o n e along
the
Dieng-B atur road,
the other
for
1
km NNE
o f
Kaw ah
Sikidang.
Data
are given
only for the
although Jacobson, Pritchard, and Keller
( 1 9 7 0 ,
p . 2 7 )
both surveys yielded resistivity
values
w h i c h w e r e similar in
t o those
measured by
the m o r e cumbersome profiling and soundi ng methods.
Dieng-B atur trav erse showed
low
resistiv ity at Pawuhan, near
Sidolok,
Timbang.
The
trav erse
NNE of Sikidang
showed a near-surface layer
6 0 thick w i t h a resistiv ity near 100 ohm-meters
un derlain
by
o f
somewhat lower resistivity. Resistivities near Sikidang
itself
quite low, as expected
from
the extensiv e fumarolic activity.
Geochem ical
Survey
geochemical
survey
o f the hot springs,
fumaroles,
and
streams
of
the
and n eighborin g areas
w as
carried out
in
August,
1970
by
. H . Truesdell of the U.S.
Geological
Survey.
A
prelimi nary report o n
w o rk
w a s
sub mitted t o
USAID on August 2 4 ,
1 9 7 0 . The
final
geochemical
(Truesdell, 1971) w as
delayed pendi ng
receipt o f geochemical analyses
USGS laboratorie s i n
Menlo Park.
systems
may
p roduce either
a
m ix ture
of hot-water and
s team ( a
s y s t e m ) ,
or
s team
alone ( a v a p o r - d o m i n a t e d or dry steam system).
importa nt
in geothermal
ex p lorat ion t o
determi ne
w h i c h
type o f
system
in
a giv en
area*
Up w ard transfer of 1^0 and heat o ccurs by m o v e m e n t
f
liquid
w at er
in
a
hot w a t e r
system, but
by movem en t
of
steam
in a
v a p o r -
system. Since most chlorides are not appreciably soluble in
team
below
300C, a
hot-w ater
system can be p r e d i c t e d w i t h a
high degree
f
c o n f i d e n c e
i f
the surface
springs have
appreciable chloride, generally
than 50 mg/1.
In the Dieng
Moun t ain s
the abunda nce o f fumaroles, the scarcity
of
flowi ng
springs,
and
the
low chloride contents
o f
m o s t flowi ng springs w ould suggest
a
vap or-dom in ated
system
w ere
i t no t for the high-chloride water at
Kaw ah
Sileri (173
mg/ 1 ) an d
at P ulosari
(426
mg/ 1 ) springs.
Inasmuch
as high-
chloride springs canno t be associated w i t h a dry-steam system
(White,
an d Truesdell, 1971),
the
Dieng geothermal system i s almost certainly
a hot-water system,with a probable chloride
content
o f 700
m g / 1
(Truesdell,
1971,
p .
1 1 ) .
In this
respect,
the
Dieng system
i s
likely
t o
be
similar
t o
Wairakei, New Zealand or Hengil, Iceland, but to differ
from
the two k n o w n
commercial
vap or-dom in ated
systems of
Lardarello,
Italy, and The Geysers,
California.
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8
Samples from
rivers
draining
the
Dieng Mounta ins were taken
t o
determine
J
whether any high-chloride thermal water diluted by ground water i s 1
discharging directly
into r i v e r s . Many rivers draining t h e Dieng
Mountains
I
contained chloride
i n
excess o f
background
( 1 0 - 2 5
mg/1), and in t w o rivers
( K a l i Tulis
a t
160-219 mg/1 a n d Kali
Dolok
at 61 mg/1) the chloride content
J
was quite h i g h . These
t w o
rivers drain
the
Sikidang
and Sileri
a r e a s , S
respectively, and t h e high
chloride values are
interpreted
t o
reflect
mixture o f chloride-bearing thermal water w i t h dilute meteoric
w a t e r .
On
t h e
basis o f
t h e
distribution o f thermal
activity,
Truesdell ( 1 9 7 0 )
concluded
t h a t i n
t h e
Dieng Mountains
at
depths
l e s s than 200 m there
are
three
geothermal
s y s t e m s ,
which may be interconnected
a t greater d e p t h s *
O f t h e s e , t h e Pagerkandang
system
(including
S i l e r i ,
S i g l a g a h , a n d Bitingan)
t h e l a r g e s t ,
with an area o f
2 . 5
k m ^ . Smaller systems
are
a t
Sikidang and
Tjandradimuka. The chloride-rich water
a t
Pulosari may
represent
outflow
from
either
t h e
Sikidang
o r
Pagerkandang s y s t e m .
Truesdell
( 1 9 7 0 ,
p .
1 3 )
notes t h a t the elevation
o f
K awah Sileri
i s
1875
m ,
and
he
assumes that this level
marks
the top of chloride
water
in t h e
Pagerkandang a r e a . There i s
a
4%
gradient between
Sileri a n d P u l o s a r i . I f
a similar gradient i s assumed from Pulosari
t o Sikidang, t h e
estimated
elevation
o f
chloride water under Ka wah Sikidang
(elevation 2035
m )
i s
1850
m .
The floor
o f
Pagerkandang crater
i s
at about
2 0 3 5 m . Therefore,
both
at Pagerkandang and
Sikidang a
hole
o f a t least
200 m would be
required t o
intercept chloride-bearing
w a t e r .
Hot-spring
fluid compositions,
particularly
t h e
content
o f S i O
and the
alkali
a n d
alkali-earth
r a t i o s ,
can be used
t o predict t h e subsurface
temperatures
o f
hot-water systems ( M a h o n ,
1970;
Fournier
a n d
Truesdell, 1970)
Use
o f
these chemical indicators, however,
i s
based on a number
o f a s s u m p t i o n .
( W h i t e , 1 9 7 0 ) :
1 . Temperature-dependent reactions, with adequate
supply of
constituents in t h e local reservoir
r o c k s ,
2 .
Water-rock equilibration
w i t h specific mineral assem blages
a t
high reservoir temperatures,
3 . Rapid flow o f water
from
reservoir t o surface s p r i n g s ,
4 .
Negligible reacti on in
transit at
lower
temperatures,
5 .
Absence o f dilution or
mixing with
other waters
a t
intermediate
l e v e l s .
White ( 1 9 7 0 )
emphasizes
t h a t
depending on discrepancies
t h a t
may
exist
between
these assumptions
a n d the actual conditions within a
s y s t e m , t h e
indicated temperatures may be only slightly
in error ( g e n e r a l l y
indicating
a
minimum) or grossly incorrect, either high o r low.
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1 0
Geologic Interpretation
Aerial
photographs w ere m ade in August, 1970 by Geotronics Surveys under
contract
AID-47
7-25-1 from USAID. Approximately 125 km^
over
the Dieng
Moun t ain s w as
flown
at
1:20,000,
an d
a n
area
of
3,500
km
2
extendi ng
from
Gun un g
Slamet east to the
Dien g Moun t ain s
and thence southeast to
Gunun g
Sumbing w as flown
at 1:35,000.
The photography
i s of
superb quality,
and
the contractor
should
be commended for doi ng an excellent
j o b .
Based on these photographs, a
photogeologic
m a p a t 1:25,000 w a s
prepared
by
GSI
(Pardyanto, 1970).
Geologic
features of particular significance
s h o w n o n the
m a p
are ( a ) the
n u m erous
young flows that radiate
from
the
volcan oes around Gunung Pakuwadja,
( b )
the^ major phreatic explosion
craters, ( c ) a zone o f
volcan ic lin eam e n t s
extendi ng northwest
from
Gun un g
B utak
t o
Pagerkanda ng
crater,(d)
conspicuous east-west structural
lineaments south o f Batur,
an d
( e ) N.10 W . structural lineaments
in the
v i c i n i t y
o f
the
Dieng-B atur road between Batur
and
Gunung
Nagasari.
The
1:50,000
geologic m a p
accompa nying the
thesis o f
Gunawa n ( 1 9 6 8 , Plate
I I )
i s
the most detailed geologic m ap
seen t o datei'. Although
there
appears
t o
be n o m a p legend, the units on the m a p can be correlated
w i t h
the thesis t e x t , w h i c h gives a detailed
sequence
o f v olcanic rocks, based
o n
geomorphic criteria. The m a p shows
in
a
general w ay the same volcan ic
and structural lineaments
that
Pardyanto ( 1 9 7 0 )
presents,
and
in
addition,
the text, Plate
X ,
and figure
2
giv e m u c h d e t a i l o n the N.10
W . and
N.10
E . lin eam e n t s defined by the explosion craters at Timbang and Gua Djimat.
Petrologic data
are contained in
Gunawa n
f
s thesis ( 1 9 6 8 ) an d
in a
pa per
by Neum an n v a n Pa da ng ( 1 9 3 6 ) . B oth writers
suggest
a sequence of
m a g m a t i c
d ifferen t iat ion
t h at
correlates well
w i t h
the
age sequence deduced
from
geomorphology. There are
no analy tical
ages, and no fossil
control.
All
o f the
volcan ic
rocks appear t o be o f Quaternary age ( l e s s than 3 m i l l i o n
years).
Although there
hav e
been numerous historic phreatic eruptions,
only
one
truly
volcan ic
( i . e . , mag ma tic) eruption
from the
Dieng
Moun t ain s
has
been reported
in historic time, that
o f
Gunung Pakuwadja
in
1 8 2 6
(Gunawan,
1 9 6 8 ,
p . 8 9 ) .
* /
A v olcanic lineament as
used
in
this
report i s a linear array of
d iscrete
v olcanic eruption points.
A structural lineament
i s an alinement
o f to pographic o r v egetativ e features that reflect a fracture o r fault in
the
earth.
B oth
volcan ic
lineaments
and
structural lineaments are commo nly
interpreted t o
be
surface expressions o f
deep zones
o f fracture
or weakness
in the earth.
- f c
Regretably,
Gunawa n's m a p
an d
thesis w ere not ma de av ailable either
t o Pardyanto
for
use
i n his photogeologic evaluation, t o Truesdell for use
in locati ng fumaroles an d
hot
springs, or t o
Muffler in
1 9 7 0 . Early access
t o
Gunawan* s
w ork could have greatly simplified and expedited the
w o rk
o f
all three scientists.
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1 1
summary of these three sources of geologic
data,
the
Dieng
Moun t ain s
a complex of separate extrusions (lavas and p yroclastic cones)
in composition through the
Quaternary
from
early
basalt
(Gunung
through oliv ine-bearing
andesite, pyroxen e andesite, hornblen de
(Gunung Butak) t o the young
biotite
andesites of the m o u n t a i n s
Gunung Pakuwadja. Laharic breccias,
ash,
and some lake sediments
complexly
intercalated w i t h
the
pyroclas t ic
cones
and
lav a
flows*
The
itself
i s a
tuff-
and
sedi ment-filled
to pographic d e p ression
extrusions.
canic lineaments are obvious: ( a ) a line of craters and flows
the m o u n t a i n crest east o f Gunung Butak
( f i g *
l )
b ) a zone of craters extendi ng southeast from Pagerkanda ng
crater
to
Pakuwadja
and
thence
m any miles
southeast to Gunung Sundoro and
Sumbing ( s e e figure 2 of Muffler, 1970).
geothermal systems
o f the Dieng
Moun t ain s
are clearly related to the
structural
lineaments. The resistiv ity
d a t a ( f i g . 1 ) show
the thermal
areas
of Pagerkanda ng and Sikidang are probably
a t d e p t h t o
form
a
single geothermal system, here named the Dieng
system. This geothermal system
i s
coincident w it h
the
zone
of
lineaments that extends from Pagerkanda ng
crater
t o Gunung
The area of most intense surface thermal activ ity ( i n and
the
Pagerkanda ng crater)
i s
at the intersection of this
n orth w es t-
and the east-west volcanic lineament along the crest of
t he
smaller
and probably separate Tjandradi muka geotherm al
falls
o n this
same east-west v o l c a n i c lineament
at
its in t ersect ion
the
N .
10W.
structural
lineaments o f Timbang, Gua Djimat, e t c .
associat ion
o f the two geothermal systems w i t h tectonic zones of
(characterized
by fracturing and
volcan ic
activity) suggests that
permeability at
d e p t h
in the g e o t h e r m a l
systems
w i l l be
d u e
t o
fractures,
as at
The
Geysers
in
California. There is n o
in the Dieng Moun t ain s for an extensiv e cap-rock overlying a
d efin ed
reservoir,
as seems to
be
the case
a t
Larderello,
Italy,
in many oil fields.
^Tazieff,
Marinelli , and Gorshkov ( 1 9 6 6 )
ap p ear
to
placed excessiv e
emphasis
on the possibility that the
basin -fillin g
of the Dieng
Plateau could form a
cap rock. Data
acquired d urin g
present inv estigations
show that
these sediments overlie
only
a
small
part
the
Dieng geothermal system
as
d e f i n e d by the resistivity
l o w .
There
well be
layers o f
restricted permeability at d e p t h in
the
Dieng
and indeed the existence o f such
layers m ay
be
importa nt
in
field characteristics under exploitation. But one can n ot
predict'
existence or location of such layers
from
available
surface data,
and
the cap
rock concept
in
the
Dieng
Moun t ain s
i s
of little p ract ical
in geothermal exploration.
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1 2
RECOMMENDATIONS
I n view o f t h e favorable f i n d i n g s f r o m t h e i n i t i a l i n v e s t i g a t i o ns , i t i s
r e c o m m e n d e d t h a t
e x p l o r a t o r y d r i l l i n g i n
t h e
D i e n g
g e o t h e r m a l
s y s t e m be
undertaken f o l l o w i n g
t h e
g e n e r a l p r o c e d u r e
o f
s t e p
2
o f
t h e
program
o u t l i n e d b y
Muffler ( 1 9 7 0 , p . 1 1 ) .
S e v e r a l s l i m c o r e
d r i l l h o l e s s h o u l d
b e d r i l l e d t o
a p p r o x i m a t e l y
2 0 0 m e t e r s
t o d e t e r m i n e
t e m p e r a t u r e g r a d i e n t s ,
c a l i b r a t e
t h e
g e o p h y s i c a l d a t a ,
a n d
acquire
f l u i d a n d
r o c k
s a m p l e s .
A f t e r c o m p l e t i o n
o f t h e s e 2 0 0 - m e t e r h o l e s , t w o h o l e s s h o u l d be d r i l l e d
t o
a p p r o x i m a t e l y
6 5 0 m e t e r s . T h e p u r p o s e s
o f
t h e s e 6 5 0 - m e t e r
h o l e s
a r e t o
d e t e r m i n e t h e
b a s e t e m p e r a t u r e
o f t h e g e o t h e r m a l s y s t e m , t o
allow c o l l e c t i o n
o f f l u i d s a m p l e s , a n d
t o
a l l o w t e s t i n g o f t h e p r o d u c t i o n c h a r a c t e r i s t i c s
o f
t h e
g e o t h e r m a l s y s t e m .
I t
is m y
r e c o m m e n d a t i o n ,
an d t h e r e c o m m e n d a t i o n of
the o ther four m e mber s
o f the e val u at ion team, that
the
e x p l or at ory
d r i l l i n g
p r o g r a m i n c l u d e
si x
h o l e s
e ach
2 0 0
m e t e r s
d e e p r a t h e r t h a n
t h e f o u r
or igin al ly
s u g g e s t e d by
Muffl e r
(1970).
The
a d d i t i o n a l cos t for the t w o
ex tra
ho les sho uld no t
exceed $50,000 an d m i g h t be s ign if ican t ly
less.
The
two
a d d i t i o n a l h o l e s
a r e
p r op os e d
to
e v a l u a t e
p a r t s
of the D i e n g ge ot h e r m al sys t e m tha t cou l d
n o t b e
ad e q u at e ly as s e s s e d by
i n f e r e n c e
f r o m only four holes.
I ndi v i dua l
si tes a r e s h ow n o n
f i g u r e
1 . A l t h o u g h the si tes
a re
s h ow n a s
points,
they
a re no t
to
be i n t e r p r e t e d
as
exa c t lo c a ti o n s tha t c a n n o t be
c h a n g e d
by
a
f e w ten s or ev en
1 0 0
m eters.
T he superv i si n g geo lo g i st
or
e n g i n e e r s h o u l d h a v e l a t i t u d e
to
shi ft p r e c i s e l o c a t i o n s t o m i n i m i z e
l o g i s t i c
or e n g i n e e r i n g problems.
I ndi v i dua l
sites,
li sted in
o r d e r
of d e c r e a s i n g p r i o r i t y a r e as follows,
w i t h m e t r ic coor d in at e s re f e r r in g
t o
f igu r e
1 :
1
Within
t h e P a g e r k a n d a n g
C r a t e r ( 8 9 , 0 5 0 N ; 3 7 , 8 5 0
E ) ; e x a c t
l o c a t i o n within
t h e
c r a t e r
i s n o t
i m p o r t a n t . T h e s i t e
i s
s u g g e s t e d
a s a p r i m e
t a r g e t b y
t h e
g e o p h y s i c s ,
t h e g e o c h e m i s t r y ,
a n d t h e g e o l o g y . A c c e s s
t o
t h e
s i t e will
r e q u i r e r o a d
w o r k ,
p o s s i b l y i n c l u d i n g c o n s t r u c t i o n o f a b r i d g e o v e r K a l i
D o l o k .
T h e c o n s e n s u s o f
t h e e v a l u a t i o n
t e a m a n d
M e s s r s .
F o w l e r , S u t a r d o n o ,
a n d
K l e p p e r
was t h a t
upgrading
o f
an e x i s t i n g b r o a d t r a i l up
t h e
s o u t h e a s t
s i d e o f
t h e c r a t e r
f o r
a
d i s t a n c e
o f a b o u t 1 km w o u l d
p r e s e n t f e w e s t d i f f i c u l t i e s . A g r o u p o f s p r i n g s
a n d s e e p s
a t t h e
c r a t e r
bottom w o u l d
p r o v i d e a s o u r c e
o f
d r i l l
water
d u r i n g t h e
r a i n y s e a s o n .
T h e s e s p r i n g s
a r e r e p o r t e d
t o
d r y
u p d u r i n g
t h e
d r y
s e a s o n ;
i f
t h e y d o ,
w a t e r will
b e
a p r o b l e m .
2 A s i t e s o u t h w e s t o f T e l a g a T e r u s
( 8 6 , 5 0 0
N ; 3 9 , 6 0 0 E ) on
t h e
margin
o f
t h e l o w r e s i s t i v i t y
a r e a a t K a w a h
S i k i d a n g . T h e s i t e
i n d i c a t e d i s a t a s u f f i c i e n t d i s t a n c e
f r o m o b v i o u s ,
vigorous
t h e r m a l a c t i v i t y
t o
p r o v i d e g o o d
g r o u n d f o r
t h e s h a l l o w p a r t s o f
t h e h o l e a n d t o o t h e r w i s e minimize l i k e l i h o o d o f o p e r a t i o n a l
p r o b l e m s a n d h a z a r d s . N o r o a d c o n s t r u c t i o n
s h o u l d
be n e c e s s a r y ,
a l t h o u g h s o m e s t r e n g t h e n i n g
o f
t h e
b r i d g e a c r o s s K a l i
l u l i s
may
b e r e q u i r e d .
W a t e r
c a n b e o b t a i n e d
from
K a l i T u l i s , 1 0 0
m
t o
t h e
s o u t h e a s t .
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1 3
3 .
This site
( 8 8 , 4 2 5
N ; 38,600 E ) on
t h e
bench
j u s t
north
of the
village o f Pawuhan i s chosen
t o
evaluate
t h e
southeastern part
o f t h e Pagerkandang 2 . 5 ohm-meter resistivity
low
a t
the lowest
feasible
drill
collar
elevation
( 2 , 0 2 5
m )
and t o see
i f
t h e
Pagerkandang center o f thermal activity extends
t o
t h e southeast
a t d e p t h . Access could
be
v ia the road constructed to
Pagerkandang
c r a t e r . Drill
water
i s available from Kali D o l o k .
4 . A
s i t e
( 8 5 , 3 0 0 N ; 39,675 E ) north
o f t h e
road junction 750 m east
o f
t h e
village
o f Sekunang, i s chosen t o evaluate
t h e
southeast
ward extension
o f the
resistivit y anomaly
a n d t o s e e
whether the
geothermal reservoir i s continuous a t depth between Sikidang an d
t h e fumaroles
a t
Telaga Tjebong. Access problems are minimal;
t h e nearest water appears
t o
be
a t S e k u n a n g , a
distance
o f
about
800 meters.
5 .
A site ( 8 8 , 2 2 5 N ;
37,000
E ) southeast o f t h e
village
of
Sidolok
on the Dieng-Batur road
i s
chosen
t o
t e s t whether or not t h e
l o w
resistivity
zone shown on
the
modified Schlumberger survey
represents a deep thermal
anomaly or merely
near-surface outflow
from Kawah
S i l e r i .
Access
i s n o
p r o b l e m ;
water
probably
can
be
had
from Kali Dolok
o r
related irrigation
c a n a l s within 2 0 0
meters
o f
the
s i t e .
6 . A site
( 8 7 , 6 2 5
N ;
39,875
E ) about 1 / 4 km west o f
Dieng
Wetan and
about 1/2
km
south o f
Dieng Kulon
i s chosen t o evaluate
whether
o r
n o t
the
geothermal anomaly extends
t o t h e northeast
side
o f
t h e
Dieng
P l a t e a u .
Access
i s e a s y , a n d
water
can
be
obtained
from t h e immediately
adjacent Kali
T u l i s .
T h e order o f
priority given
i s not
necessarily t h e
order i n
which t h e holes
should
be
d r i l l e d .
The Pagerkanda ng
a n d
Telaga
Terus holes
are
likely
t o
be in the hottest ground and t o
present
greatest drilling problems.
Accordingly, perhaps a hole such
a s
Pawuhan
o r Sidolok s h o u l d
be
drilled
f i r s t , i n
order t o
allow
t h e
contractor
t o
gain
experience i n local
conditions
and
I n t h e problems o f geothermal d r i l l i n g .
There should be sufficient latitude in t h e drilling contract for t h e
supervising geologist or engineer
t o
terminate
a
hole
a t
depths shallower
than
2 0 0
m o r
t o
drill onward
f o r
several tens o f meters beyond 200 m
s h o u l d
conditions
warrant.
There i s nothing magic a b o u t t h e
2 0 0 m number;
i t
was
chosen
a s a
figure
which
on t h e
average
should be deep enough t o
allow acquisition o f information needed
t o
more
fully evaluate t h e
geothermal
s y s t e m .
Drilling at Tjandradimuka i s n ot
recommended
a t present f o r four reasons:
1 . The
small
size of
t h e
resistivity
a n o m a l y .
2 . Difficult a c c e s s .
3 . History
o f
violent phreatic eruptions
a t
Timbang
t o t h e
southwest
a n d
Gua Djimat t o
t h e southeast.
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A .
Presence o f
toxic gases at
Timbang
and
Gua
Djimat.
Sites for the
650-m holes
should not
be
selected
until
most o f t h e
data
from t h e 200-m holes are a v a i l a b l e .
( T h i s
was Muffler's 1970
i n t e n t ,
although his report
i s n o t explicit i n t h i s respect.) The
650-m holes
should
be
sited
principally on t h e basis
o f thermal gradients
determined
from
t h e 200-m
h o l e s ,
keeping i n
m i n d
that
t h e
primary object o f
t h e
650-m holes i s t o determine
t h e
base
temperature o f
t h e
geothermal s y s t e m .
I t
i s
obviously inappropriate t o
s i t e a n y
development holes until both
t h e
200-meter and 650-meter exploratory holes are drilled
a n d
the results
(including geochemical sampling and analysis of f l u i d s ) a r e a v a i l a b l e .
OBJECTIVES AND REQUIREMENTS OF DRILLING
Drilling
should
be conducted s o
as t o
achieve
t h e
objectives outlined on
p . 1 1 o f
Muffler's
report ( 1 9 7 0 ) .
The 200-meter holes
should
be
designed
t o :
a .
Determine
temperatures
a n d
temperature gradients,
b .
Allow collection o f water
a n d gases
from
the
holes
after
completion o f drilling
c .
Sample
t h e rocks
drilled
d . Test
t h e
geophysical, geochemical, and geological i n d i c a t o r s .
An accurate
determination
o f t h e temperature gradient from 100 t o 2 0 0
meters
i s
i m p o r t a n t . Recent USGS research drilling in Yellowstone National
P a r k ,
Wyoming, U S A , has
shown t h a t t h e
only accurate method
o f
determining
p r e -
drilling
ground temperatures i n geothermal areas i s t o drill f o r no longer
than
eight h o u r s , . l e t the
hole
stand f o r 1 5 hours, and t h e n take a bottom-
hole tem perature^
.
Accordingly,
a t
depths
of
100 t o
2 0 0
meters, drilling
should
progress
a t n o
more
than 3 3
meters per
d a y ,
s o
t h a t four o r
more
In
the Yellowstone
d r i l l i n g , i t
was feasible
t o leave t h e rods i n t h e
drill hole overnight
a n d take the
bottomhole temperature through
the rods
a n d t h e drill b i t .
I n
caving
g r o u n d ,
i t
may
n o t
be
possible
t o
leave t h e
rods in the
hole
overnight
without danger
of them
becoming
s t u c k .
I f
drill
mud
i s
u s e d ,
i t
may
prove impossible t o lower
a
temperature probe
t o
t h e
hole bottom through
t h e
mud
after i t
has
settled
for 1 5 h o u r s . I f
s o ,
i t
may be necessary t o
l o w e r t h e
probe
j u s t
after
t h e e n d o f t h e
drilling s h i f t ,
a n d
leave the probe a t hole bottom overnight.
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1 5
temperatures
can be
determi ned from
1 0 0
t o 200 m e t e r s
d e p t h * - .
m ad e t o determi ne bottomhole temperatures at depths
than
100 m e ters
whenev er feasible.
of w a t e r a n d gases should
be
collected from
the
holes after
o f
d rillin g and
recovery
of the
hole
f r o m
drill-water loss.
the hole shows a tendency to cave, slotted liner should
be
hung
in
the
s o that
there will be conti nuing access t o
all
d e p t h s of the
hole
fluid sampling.
The min im u m
internal diameter of
the
liner should
be
least 2 - 1/4 inches ( 5 . 7 2 c m ) t o
allow
2-inch O.D. sampling dev ices t o
Accordingly, holes
should
be drilled at a dia meter sufficient
allow slotted
liner o f at least 2-1/4 inches I . D .
to be
inserted.
w o u l d
be ideal t o hav e
the
holes cored throughout their total d e p t h
20
m e ters
or s o , but this may no t be
fin an cially
feasible. Some core,
least
every 30 meters,
i s
essential, however, to
permit laboratory
o f
physical properties such as porosity, den sity,
e t c . This obviously
w ill
require a dia mo nd drill rig
w i t h
capability.
Assum in g
t h at
the rig i s equipped for wire-line
o f core,
i t
may not cost appreciably m o r e t o
core
conti nuously
t o
core only
intermittantly.
These alternativ es should be explored
possible contractors.
are
t w o
p ossible programs
for interrelati ng the
20 0 -meter
a n d
the
holes:
1 . Drill t he 20 0 -meter holes at a dia meter sufficiently
great
t o
allow
a
string
o f
casing to be cemented
in a t
20 0 -250 m eters,
retaini ng sufficient diameter
w i t h i n
this
casing
t o
allow
d rillin g
t o
proceed
safely and successfully t o
650
meters.
2 . Drill the 20 0 -meter
holes
at
small
diameter s, and drill completely
n e w
650 -meter holes
after thorough
e v a l u a t i o n o f best diameters
and casing program.
There are
a number
of
ways of
m easurin g
temperatures at depth.
ters, thermocouples, resistance t hermo meters and other electrical
accurate
and
efficient
w h e n they
work,
but in
a
number of
d rillin g
projects ( e . g . ,
Yellow s t on e
and Nicaragua)
they
have
a
d is tressin g
tendency
t o fail,
owi ng
t o
shorti ng
of the
cable
or
t o
of
the po tti ng
compound
under the
high-tem p erature
condi tio ns
and
the presence o f
a n
electrically conducti ng fluid.
Maxim um -record in g
(mercury in glass) do no t have
this
p ot e n t ial
for
electrical
but care must
be
taken t o insulate
the
thermo meter w hen temperature
are
suspected. I f temperatures at
d e p t h
in the Dieng Moun t ain s
determ in ed usin g electric al methods, great care
m u s t
be taken
t o
insure
gear
i s reliable and will
n ot fail;
the Dieng Mountains are a long,
way from the
nearest point where
electronic gear can
be repaired or
At the
very
least,
several m ax im u m -read in g thermo meters
(with
tight restrictions s o
that
the mercury column i s not
shaken
d o w n
during
withdraw al) should be
o n h a n d
t o
back up the
ge ar i n
case of failure.
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1 6
A choice between these alternatives requires
c o s t and
drilling equipment
data
not
available
to m e , and s h o u l d
be
made after
preliminary consultation
with
prospective drilling contractors
a n d
after evaluation o f t h e USAID-
assisted 2,000-foot drilling program in
Nicaragua.
The drilling a n d casing
program
should be designed t o preclude any
uncontrolled eruptions
o f s f c e a m and w a t e r , particularly any
eruptions
around ( o u t s i d e ) the cas i n g Based
on t h e
nature o f the surface activity
i n t h e Dieng a r e a , i t i s anticipated t h a t t h e geothermal
water
level
will
be a t considerable
d e p t h , perhaps a s much a s 2 0 0 meters.
I f
this i s the
c a s e ,
pressures
are
unlikely
t o be
high until
t h a t
d e p t h ,
and
even
a t
considerably greater depths
pressures should be largely
counter-balanced
a n d controlled
by
the weight o f
water
standing i n t h e h o l e . However, a t
most depths there i s
some
potential f o r a surprise
e r u p t i o n , a n d
accordingly
casing
s h o u l d
be cemented
i n
t h e
hole
s o t h a t any eruption will occur through
the casing^
.
I f
there
i s
any indication
o f
pressure, an appropriate valve
a n d stuffing
box
should
be
mounted on
t h e
c a s i n g ,
a n d
drilling should be
done through
the
valve
a n d
stuffing b o x . I f wireline i s
used,
provision
s h o u l d
b e
made t o withdraw t h e core under positive pressure
within
the drill
s t r i n g .
With
regard
t o appropriate drilling operations
a n d
casing
p r o g r a m ,
i t i s
important that t h e level o f water standing i n t h e
hole
b e noted and
recorded
each d a y . Gradual rise o f water
l e v e l
on successive days can give warning
o f increasing
pressure
a n d potential drilling o r casing p r o b l e m s .
Water
level
measurements are
also
very
important scientific data essential t o
t h e
interpretation and evaluation o f t h e geothermal s y s t e m .
The wild
bores
a t T h e G e y s e r s ,
California
a n d
a t
Wairakei, New
Zealand are apparent ly both due
t o
insufficient depth
o f c a s i n g ,
with high-
pressure
steam
coming up
t h e open hole t o t h e f o o t o f the casing and then
o u t into t h e
formation
t o the s u r f a c e .
It
i s
not
possible
to g i v e
positive
guidelines
f o r casing depths a n d
number o f s t r i n g s .
I n t h e
USGS Yellowstone
d r i l l i n g ,
where
t h e
thermal
water
t a b l e
was a t the ground s u r f a c e ,
a n d
appreciable pressures
over
hydrostatic developed
a s
drilling p r o g r e s s e d , one string o f 4-1/2
x
5-1/2
inch casing
was
generally
s e t
a n d cemented a t 2 0 f e e t , and
a
s e c o n d string
o f s m a l l e r
diameter near 100 f e e t . A
t h i r d s t r i n g
was s e t
a n d
cemented
a t
about 500 feet i f much greater depth a n d higher temperatures were anticipated
I f
t h e
geothermal
water
table
i n t h e Dieng
Mountains
i s
near
the
predicted
elevation ( 1 8 7 5
m . ,
Truesdell, 1 9 7 1 ) , t h e
casing
program need
n o t
be
s o
thorough
a s a t
Yellowstone. Casing programs
f o r
developmental geothermal
wells
a r e
discussed by Giovannoni ( 1 9 7 0 ) a n d by Dench ( 1 9 7 0 ) , b u t their
discussions related
t o
deep
( 1 , 0 0 0 - 2 , 3 0 0
meter) production holes t h a t
require f a r
more
casing
o f
f a r
larger diameter t h a n t h a t
needed
f o r t h e
200-m exploratory
holes
i n t h e Dieng Mountains.
__________
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1 7
VOLCANIC, EARTHQUAKE, AND
LANDSLIDE
HAZARDS
g e o t h e r m a l
system r e q u i r e s a p o t e n t
h e a t s o u r c e
a t
d e p t h .
Although s u c h
h e a t s o u r c e h a s n e v e r been d r i l l e d
o r
s a m p l e d , various l i n e s
o f
g e o l o g i c
t h e
presence
o f
a
h o t b o d y o f i n t r u s i v e rock a t d e p t h s
f 3 km o r g r e a t e r . Meteoric w a t e r c i r c u l a t e s t o t h e s e d e p t h s , a c q u i r e s
f r o m
t h e h o t body o f r o c k , a n d
b u o y a n t l y r i s e s
t o t h e
s u r f a c e i n t h e
c o r e o f
t h e g e o t h e r m a l s y s t e m .
n m o s t
e x p l o r e d
geothermal
a r e a s ,
i g n e o u s a c t i v i t y i s
n o t
o n l y
i n f e r r e d
t h e e x i s t e n c e o f t h e
g e o t h e r m a l
s y s t e m , b u t i s directly e x p r e s s e d a t
e a r t h ' s s u r f a c e by Q u a t e r n a r y v o l c a n i c r o c k s . T h e s e r o c k s
r e p r e s e n t
o f molten rock ( m a g m a ) t h a t made
t h e i r
way
t o
t h e
s u r f a c e r a t h e r
s o l i d i f y i n g
a t d e p t h .
A
n u m b e r
o f
g e o t h e r m a l a r e a s a r e
i n
regions where
t h e r e h a s
been
h i s t o r i c
volcanic a c t i v i t y .
F o r
t h e Wairakei
g e o t h e r m a l
f i e l d i n New Z e a l a n d i s l o c a t e d
only
1 0
m
n o r t h o f Lake T a u p o ,
t h e
l o c u s
o f t h e 1 3 1
A . D .
T a u p o
Pumice
e r u p t i o n ,
world's l a r g e s t volcanic e r u p t i o n o f t h e p a s t 2 , 5 0 0 y e a r s .
geothermal f i e l d i n New Z e a l a n d i s l o c a t e d 2 5
km
n o r t h e a s t o f
T a r a w e r a ,
which
l a s t e r u p t e d i n 1 8 8 6 .
Die n g
g e o t h e r m a l s y s t e m i s a lso lo c a ted
in
a n a r e a
of
v e r y y o u n g a n d
c o n t i n u i n g
vol can is m . Al t h ou gh there
a r e
n o r a d i o m e t r i c d a t e s
n
t h e reg i o n, the p hys iogr ap hy
of
m o u n t a i n s suc h
as
G u n u n g Fakuwa dj a,
K e n d i l , a n d
G u n u n g Sun do ro
a n d
of
c ra ters
s u c h
as
P age rkan d an g,
Mer d ad a, a n d Fa n g o n e n i n d i c a t e s
that
v o l c a n i c a c t i v i t y i n the Die n g
h a s
p e r s i s t e d u n t i l v e r y
rec en t times. Indeed,
G u n u n g P a k u w a d j a
s
r e p o r t e d
to
h ave er u p t e d in
1826,
a l t h o u g h
the p r e c i s e n a t u r e o f t h e
is
n o t clea r f r o m
the
sc a n ty repo rts (Gunawan,
1 9 6 8 ).
h a v e
bee n n o t r u e v o l c a n i c
e r u p t i o n s
(i.e.,
tho se t h at
e r u p t i o n
of
m o l t e n rock) in the
Dieng Mo u n t a i n s s i n c e
1826,
there
p h r e at i c er u p t ion s o r hyd r ot h e r m al explosions^- ; t h e s e
b e e n d e s c r ib e d
in d e t ail
by
Gu n aw an (1968,
p . 9 0 -1 0 3 ) ,
an d
a r e
i n
t able 1
of
t h is rep o rt.
a p p a r e n t f r o m
tab le
1 t h at viol e n t p h r e at ic er u p t ion s or hyd r ot h e r m al
i o n s h a v e o c c u r r e d i n rec en t y ears
at
K a w a h Sileri, a n d t ha t si m i la r
c a n
be
e x p e c t e d i n the
future. Accor d in gly,
d r i l l i n g a t K a w a h
s h ou l d be
a v o i ded, an d a ny buildi n g s or
g e n e r a t i n g
f a c i l i t i e s
P h r e a t i c
e r u p t i o n s
a n d h y d r o t h e r m a l e x p l o s i o n s are
c o m m o n l y
c o n f u s e d ,
p h r e a t i c eruption s e n s u s t r i c t u o c c u r s when magma c o n t a c t s g r o u n d w a t e r ,
i t t o steam
with c o n s e q u e n t e x p l o s i v e
e x p a n s i o n producing a
A hydrothermal
e x p l o s i o n
i s
p r o d u c e d
when w a t e r c o n t a i n e d i n n e a r -
t e m p e r a t u r e s
u p
t o
p e r h a p s 2 5 0 C f l a s h e s i n t o steam a n d
disrupts
t h e
c o n f i n i n g r o c k s ; n o
m a g m a
i s d i r e c t l y i n v o l v e d . I t
s
n o t
a l w a y s p o s s i b l e t o d e t e r m i n e
w h e t h e r a
g i v e n eruption i s
a p h r e a t i c
o r a
h y d r o t h e r m a l
e x p l o s i o n , p a r t i c u l a r l y when
observational
d a t a
B o t h
t y p e s
o f a c t i v i t y s e e m t o h a v e
t a k e n
p l a c e
n
t h e D i e n g M o u n t a i n s .
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8/11/2019 ERUPTIVE HISTORY OF THE DIENG MOUNTAINS REGION, CENTRAL JAVA, AND POTENTIAL HAZARDS FROM FUTURE
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T
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8/11/2019 ERUPTIVE HISTORY OF THE DIENG MOUNTAINS REGION, CENTRAL JAVA, AND POTENTIAL HAZARDS FROM FUTURE
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1 8
should be located away from Kawah S i l e r i , probably near Dieng
W e t a n .
Any
eruptions from Kawah
Sileri
are likely
t o
be accompanied by some earthquake
a c t i v i t y , o f
uncertain but probably rather low
intensity.
Planning
f o r
any
plant construction should
t a k e
i n t o account
t h i s
potential local
s e i s m i c i t y ,
as
well
as
any regional
s e i s m i c i t y .
The l a s t truly
volcanic
eruption in the Dieng
Mountains took
place
a t
Gunung Pakuwadja in 1 8 2 6 ( 7 ) . One cannot assume
t h a t
volcanic
activity has
ceased, yet there i s no
way
t o
predict
i f ,
when,and where, another volcanic
eruption
will
o c c u r . I f a
volcanic
eruption should occur,
one might
expect
i t s locus t o be
near Gunung
Pakuwadja.
Landslides have been very common through historic
time in the
Dieng Mountains,
and
t h e
village
o f Legetang was buried i n 1955 by
a
landslide from
Gunung
Pengamun-amun ( G u n a w a n ,
1 9 6 8 , p .
6 3 ) . Telaga
Sewiwi (northwest o f
Karantengah)
apparent ly was
formed
by
a
landslide
in 1786 t h a t may
have been
triggered by the
phreatic
eruptions a t
Tjandradimuka
and Timbang. Landslid es
clearly present
a
hazard
t h a t
must be considered
i n
any generating
plant
l o c a t i o n .
ORGANIZATION OF EXPLORATORY PROGRAM
T o date there has
been
no specific organizational structure for t h e initial
investigations
o f
t h e Dieng Mountains, and no single operational and
coordinating focus
such a s a project m a n a g e r . This pattern, though
generally satisfactory, has resulted i n intermittent
confusion
a n d
misunderstanding
among
t h e
various institutions, contractors, and
individuals involved a s
t o t h e i r
specific responsibilities
and t i m e s c h e d u l e s .
There
have been
n o major p r o b l e m s , h o w e v e r , and t h e Initial Investigations
have been completed satisfactorily,
i n great
part due
t o g o o d
will and sense
o f
cooperation exhibited
by
a l l .
In particular, t h e
expediting
efforts o f
D r . Johannas
o f t h e G S I , D r .
Arismunandar
o f t h e P R I ,
D r . Klepper o f
t h e
U S G S , a n d M r . Kent a n d M r . Fowler o f USAID have
been
invaluable.
T h e evaluation t e a m , h o w e v e r , unanimously feels t h a t
a f o r m a l ,
recognized
projec t organization, p robably headed
b y a
project m anager
with clearly
defined
responsibility
a n d a u t h o r i t y , i s essential f o r t h e exploratory
drilling
a n d
any subsequent
s t e p s .
The anticipated increase
i n
c o s t ,
personnel
and
complexity greatly
increases
the potential f o r serious
misunderstandings, lack
o f coordination, and omissions. I n particular,
l o n g a n d
short-range planning
a n d
timing
o f
contracts, advisory
personnel,
a n d
supporting services i s essential.
I t i s beyond t h e scope of this report t o suggest any specific organizational
s t r u c t u r e . However,
attention
should b e
drawn t o t h e organization
o f
t h e
state-run
geothermal
enterprises i n
New
Z e a l a n d , I t a l y , a n d J a p a n .
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1 9
SUPPORTING
GEOLOGICAL AND GEOPHYSICAL INVESTIGATIONS
Although n o t required f o r assessment
o f
the geothermal resources
o f
the
Dieng Mounta ins, several
l i n e s
o f scientific investigation could
well
provide
d at a
useful
i n
planning
t h e development o f the f i e l d .
I t
i s t h e
hope o f
t h e
evaluation
team
t h a t t h e s e investigations might be investigated
by t h e
cooperating
institutions during t h e coming year s o t h a t s o m e results
would be available
in t h e e v e n t a
decision i s made t o proceed with
development
o f t h e
f i e l d .
I t i s recommended
t h a t
regional photogeologic analysis o f the 3,500 km^
covered by t h e
1:35,000
aerial photographs be completed.
Preliminary
assessment i s currently being made by W .
H . C o n d o n , U S G S .
Gravity
studies i n t h e
Dieng Mountains
may prove
useful
i n
determining
t h e thickness
o f
the inter-volcano sediments i n t h e Dieng-Sikidang area
a n d
i n
t h e flat lands surrounding B a t u r . An initial gravity survey i s
currently being conducted along t h e Dieng-Batur road
by t h e
G S I . I f
t h e
results
o f
t h i s survey
are
f a v o r a b l e , i f
may
be
appropriate to
extend t h e
survey throughout the Dieng M o u n t a i n s .
I t i s
a l s o
recommended t h a t a microseismic
monitoring
system be installed
i n t h e
Dieng
Mountains. Such a
monitoring
system
would
serve t h r e e
p u r p o s e s :
1 . T o locate
earthquake
epicenter concentrations t h a t may indicate
deep geothermal targets
( c f .
Ward
a n d
Bjornsson,
1971; W a r d ,
Palmason, a n d D r a k e , 1 9 6 9 ; Lange a n d
Westphal, 1 9 6 9 ) *
2 . T o detect
any
increase i n frequency o f
microearthquakes
o r
change
in
location
o f e p i c e n t e r s , i n
order
t o
anticipate
possible
volcanic
(including p h r e a t i c ) e r u p t i o n .
3 . I f development o f
t h e
geothermal field proceeds, to
monitor
any increase
i n number o f
microseismic
events
related
t o large-
s c a l e fluid
withdrawal
( H e a l y ,
R u b e y ,
Griggs,
a n d
Raleigh, 1 9 6 8 ) .
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2 0
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