Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

Hydrothermal system of the Papandayan Volcano,West Java, Indonesia and its geochemistry evolutionof thermal water after the November 2002 eruptionAGNÈS MAZOT*, ALAIN BERNARD*,
and IGAN SUPRIATMAN SUTAWIDJAJA***
Department of Earth and Environmental Sciences, CP 160/02,
Université Libre de Bruxelles, 50 Ave. Roosevelt, 1050 Brussels, Belgium**
Center for Volcanology and Geological Hazard Mitigation,
Jalan Diponegoro 57, Bandung, Indonesia 40122

ABSTRACT
Papandayan is a strato volcano situated in West Java, Indonesia. After the last magmatic eruption
in 1772, only few phreatic explosions have been occurring. At the present time, the activity is centeredin the northeast crater manifested by the presence of fumaroles and hot springs. In November 2002
an explosive eruption occurred and ejected ash and altered rocks. Study of the altered rocks revealed
that an advanced argillic alteration took place in the hydrothermal system by an interaction between
acid ﬂuids and rocks. Four zones of alteration have been formed as a limited extension along faults or
across permeable structures at different levels beneath the active crater of the volcano.
Two types of acid ﬂuids are distinguished in the crater of the Papandayan Volcano: (1) acidsulphate-chloride water with pH values between 1.6 and 4.6, and (2) acid sulphate water with pH
values between 1.2 and 2.5. The samples collected after the eruption revealed an increase in the SO4/
Cl and Mg / Cl ratios. This evolution is likely explained by an increase in the neutralization of acidﬂuids which tends to show that water-rock interactions were more signiﬁcant after the eruption. Thechanges in chemistry observed in 2003 were the consequence of the opening of new fractures where
unaltered or less altered volcanic rocks were in contact with the ascending acid water. The high δ34S
values (9-17‰) observed in the acid sulphate-chloride water before the November 2002 eruption
suggest that dissolved sulphates were mainly formed by the disproportionation of magmatic SO2. On
the other hand, the low δ34S values (-0.3-7 ‰) observed in acid sulphate-chloride water sampled after
the eruption suggest that the origin of dissolved sulphates for these waters is the surﬁcial oxidation ofhydrogen sulphide.
Keywords: Papandayan Volcano, phreatic eruption, hydrothermal system, ﬂuid geochemistry,advanced argillic alteration
SARI
Papandayan adalah gunung api strato yang terletak di Jawa Barat, Indonesia. Setelah erupsi
magmatik terakhir pada 1772, letusan yang terjadi hanyalah bersifat freatik. Pada saat ini, kegiatan
vulkanik terpusat pada kawah sebelah timur laut berupa fumarola dan mata air panas. Pada
November 2002, terjadi letusan eksplosif yang memuntahkan abu dan batuan alterasi. Studi batuanalterasi menunjukkan bahwa perkembangan alterasi argilik yang terjadi dalam sistem hidrotermal
merupakan interaksi antara cairan asam dengan batuan. Empat zona alterasi yang terbentuk terbatas
pada rekahan sepanjang sesar, memotong struktur lapisan lolos air yang berbeda-beda lapisan di
bawah kawah aktif gunung api ini.
Dua macam cairan asam yang berbeda pada kawah Gunung Api Papandayan, yaitu: (1) air
asam sulfat-klorida dengan pH berkisar antara 1,6 dan 4,6, dan (2) air asam sulfat dengan pH

15

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Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

antara 1,2 dan 2,5. Pengambilan percontoh setelah erupsi menunjukkan peningkatan pada rasio
SO4/Cl dan Mg/Cl. Evolusi ini tampaknya mencerminkan peningkatan dalam netralisasi cairan asamyang cenderung menunjukkan bahwa interaksi air-batuan adalah tipe kontak dengan meningkatnya
air asam. Tingginya δ34S (9-17‰) yang teramati di dalam air asam sulfat-klorida sebelum erupsi
November 2002 menunjukkan bahwa larutan sulphate terutama terbentuk karena ketidak seimbangan
SO2 dalam magma. Sementara, rendahnya δ34S (-0,3–7‰) yang teramati di dalam contoh air asam
sulfat-klorida setelah erupsi menunjukkan bahwa larutan sulfat yang berasal dari air tersebut
merupakan oksidasi permukaan hidrogen sulfida.
Kata kunci: Gunung Api Papandayan, erupsi freatik, sistem hidrotermal, cairan kimia, alterasi
argilik lanjut

INTRODUCTION
Papandayan Volcano produced a catastrophic
debris avalanche during the brief magmatic eruption
in 1772. Afterwards, only small phreatic eruptions
had occurred prior to the more explosive eruption
in November 2002 which has changed the crater
morphology. Today, the volcano activity is reduced
to be the presence of fumaroles with sulphur-mud
pools and hot springs. The geochemical survey offumaroles and thermal springs can provide useful
information on the state of activity of the volcano,on the relationship between the hydrothermal andthe structural systems of the volcano and on theactivity evolution with time (Fischer, 1997; Taran,
1998; and Federico, 2002). Changes in the chemicalcomposition of gases and/or hot springs may reﬂect
an interaction more or less important between the
deep ﬂuid and the superﬁcial aquifer (Ohsawa,
1993; Valentino, 1999; and Tassi, 2003). But, theseevolutions may also be the consequence of an increase in the volcano activity that could generate aphreatic eruption (Nogami, 2000), or a magmaticone (Giggenbach, 1990; Takano and Watanuki,
1990; Arribas, 1995; and Fischer, 1997). The recent
activity ejected ash and altered rocks coming fromthe inside of the hydrothermal system offers an opportunity to improve our knowledge on the alteration
processes occurring at depth (Christenson and Wood,
1993). This paper presents the results of chemical
and isotopic studies of hot-spring waters sampledfrom 1994 to 2002. After the phreatic eruption that
occurred in November 2002, new hot-spring waters
were collected for chemical and isotopic analyses,
whilst volcanic ashes and altered rocks were also
sampled for mineral analysis. The chemical andmineralogical data serve in having a better under-

standing about the alteration by the acid-ﬂuids on
the rocks in the hydrothermal system and allow to
observe changes in the activity of the Papandayan
Volcano which has already produced a catastrophic
magmatic eruption in its historical time.

VOLCANO SETTING AND
THE NOVEMBER 2002 ERUPTION
The Papandayan Volcano is a stratovolcano(7°32’ S, 107°73’ E, 2665 m a.s.l.) located at 180
km to the southeast of the Jakarta (Figure 1). During its historic activity, the eruptive center moved
to the northeast with the formation of successive
new craters. The deposits in this area consist of
Tertiary andesitic lava ﬂows overlain by numerous
alternating pyroclastic ﬂows and falls with andesite
basaltic lavas. The last magmatic eruption of the
Papandayan Volcano occurred in 1772. A debris
avalanche created a horseshoe-shaped crater open
to the northeast and covered an area of about 250
km2, resulted in the destruction of 40 villages and thedeath of 2957 inhabitants (van Padang, 1951). The
last reported activity, during June 1998, consisted ofincreased seismicity and minor phreatic explosions(USGS, 1998). Until November 2002 eruption, thehydrothermal activity was centred in the crater (1× 1.5 km) with multiple fumaroles, mud-pools andhot springs.
In Early October 2002, the seismicity of the
volcano increased and small phreatic explosions occurred in the crater (USGS Volcanic Activity Report,
2002). On 11 November 2002, a phreatic eruption
from the southeast of the crater caused a landslidethat became a lahar. On 15 November 2002, a phreatic eruption ejected steam and an ash plume up toHydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)4000 m above the crater. Earth Probe TOMS (Total
Ozone Mapping Spectrometer) instrument detected
small amount of SO2 on November 13 (<1500 tons).
On November 15, SO2 was again detected, in a small
plume extending west of Papandayan. The estimated
SO2 mass was 7000 tons. Between 16 and 20 November 2002, explosions ejected an ash plume up to 700
m high then followed by landslides and lahars. On 20
November, another major eruption took place at thenorthwest of the crater. Ash plume reached 1500 m
above the vent and the cloud drifted to the northeast.
The eruption also produced a directed blast as far as
2 km and left blocks and smaller fragments of alteredrocks and 4-8 cm thick deposit of wet ashes. Breadcrust bombs with maximum diameter of 50 cm were
found. During the next month, the activity decreased
and actually only fumarolic manifestations were
present (USGS Volcanic activity report, 2003). New
vents have been created with one containing a smalllake, and another mud-pool and new hot springs
appeared (Figure 1).

17

SAMPLING AND ANALYTICAL METHODS
Water samples were collected from 1994 to 2005
in the crater (Figure 1). The pH was determined in
the ﬁeld after calibration with pH 1 and standard
reference buffers. The concentrations of cations were
measured by inductive coupled plasma optical emission spectroscopy (ICP-OES) whereas the anions
Cl-, SO42- and F- were analyzed by high performanceliquid chromatography (HPLC). Furthermore, theδ34S of sulphates were determined by mass spectrometry. Products of 2002 eruption collected around the
new vents consist of grey ashes and altered rocks.
Their mineralogy was determined by means of an
X-ray micro diffraction instrument equipped with a
HISTAR detector. A scanning electron microscopy(SEM) and an energy-dispersive X-ray spectrometer(EDS) were also used to study the ejecta. The EDS
detector was equipped with a NORVAR windowthat enables the detection of elements with atomic
number (Z) above 3.

RESULT OF INVESTIGATIONS

Figure 1. Location map of the Papandayan Volcano. The
faults and vents appearing during November 2002 are also
highlighted.

Mineralogy of Erupted Products
The altered rocks are derived from highly alteredlavas of andesitic compositions. Some samples show
a complete siliciﬁcation. Bread crust bombs comefrom the eruption of 20 November 2002, the most
explosive of this period. Rock and ash alteration
mineralogy is summarized in Table 1. The mostabundant phases are cristobalite (XRD patterns on
Figures 3a and 4a), quartz (XRD patterns on ﬁgures
3b and 4b), pyrite (Figures 2a and XRD patterns
on Figures 3b and 4) or marcasite (XRD pattern on
ﬁgure 4a), pyrophyllite (Figure 2b and XRD patterns
on Figures 3b and 4b) and alunite (Figure 2c). The
alunite phase identiﬁed is a natroalunite ((Na0.5, K0.5)
Al3 (SO4)2 (OH)6), based on XRD analysis (Figure4a). Sometimes some radiating pyrite or marcasite(Figure 2d) has been found in ejectas covered bysmall crystals of alunite. In experimental studies(Murowchick and Barnes, 1986), the occurrenceof marcasite indicates: (1) a ﬂuid relatively acid(pH<4-5), (2) a temperature of deposition below 240°C and post-depositional temperatures that remain
below 160°C and (3) the presence of polysulphides(e.g. H2S2) that are formed by partially oxidation

18

Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

Table 1. Alteration Phases in Ejecta from the November 2002 Eruption

Samples

Cristobalite

Opal-CT

QuartzEjecta
PAP_01

X

X

PAP_02

X

X
X

PAP_03X

PyriteX

Marcasite

X

X

PAP_05

X

X

PAP_06

X

X

X
X

X

X

PAP_08

X

X

X

X

PAP_09X

PAP_10X

PAP_11

Pyrophyllite

Natroalunite

X

X

X

X
X

PAP_13

X

X

X

X

X
X

X

X

X

X
X

X

X

GypsumX

X
X

Anhydrite

X

X

PAP_12Kaolinite

X

PAP_04

PAP_07NativeSulfur

X

Ashes
Ash1

X

X

X

X

X

X

X

Ash2

X

X

X

X

X

X

X

Ash3

X

X

X

X

X

X

X

X
X

Ash4

X

X

X

X

X

X

Ash5

X

X

X

X

X

X

Ash6

X

X

X

X

X

X

X

X

Ash7

X

X

X

X

X

X

X

X

of sulphides species (e.g. H2S) close to the site ofdeposition. Marcasite has been found coexisting with
pyrite, quartz and/or alunite in high altered rocks.
Anhydrite (Figure 2e and XRD pattern on ﬁgure 3b)
or gypsum and kaolinite (XRD pattern on Figure 4b)
are sporadic phases. The accessory minerals are, inaltered rocks, rare enargite, rutile or anatase inclusions in pyrite and muscovite. The bread crust bombshows many phenocrysts of plagioclase, hyperstheneand augite in a gangue of glass plus crystals ofprincipally plagioclases and pyroxenes (Figure 2f).
This bomb is not altered and is characterized by afragment of lava without vesicles and contains many
phenocrysts.
Four alteration assemblages have been determined in altered rocks. The ﬁrst assemblage consistsof pyrophyllite, quartz ± cristobalite ± natroalunite± anhydrite ± pyrite ± native sulphur and gypsum(PAP-01, PAP-08, PAP-09, PAP-10 and PAP-11).
The second assemblage contains kaolinite, quartz,
cristobalite, natroalunite, anhydrite and pyrite (PAP05). The third suite is composed of natroalunite,
pyrite, cristobalite and ± marcasite (PAP-04 and
PAP-06). The last assemblage consists of quartz ±cristobalite ± pyrite and ± marcasite (PAP-02, PAP03, PAP-07, PAP-12, PAP-13).

X

Composition of Volcanic Gases
Chemical compositions of volcanic gases fromthe crater of Papandayan Volcano (Figure 1) arepresented in Table 2. The crater discharged gases
up to 400°C in 1994-1996, and in 2004 after the
eruption, the maximum temperature measured was
260°C. The gases collected in the fumaroles consist
mostly of H2O with minor amount of CO2 and H2S
and very low SO2 and HCl contents.
Composition of Thermal Water
The analysis result of hot spring water collected
since 1994 are shown in Table 4. Several hot springs
are present on the west and south sides of the craterwith mud pools close to solfataras (Figure 1). Considering the data on Table 3, two groups of springs
can be distinguished: acid sulphate-chloride and acidsulphate water. Acid sulphate-chloride water have
pH varying from 1.6 to 4.6, temperatures between
17 and 94°C and TDS concentrations between 506 to
8380 mg/l. A crater lake was formed during the November 2002 eruption and belongs to the same typeof acid sulphate-chloride water. Acid sulphate (orsteam condensates) water containing high sulphateconcentration but low amounts of chloride, have pH
values between 1.2 to 2.5, temperatures between 23

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)19

Figure 2. Secondary electron image (SEI) photomicrographs (a, b, c, and d) and back scattered electron image (BEI)
photomicrograph (f) of altered minerals. (a) Octahedral pyrite in ejecta, (b) Crystal of clay (pyrophyllite or kaolinite) in ash,(c) Rhombohedral alunite in ejecta, (d) Radiating pyrite or marcasite covered by crystals of alunite in ejecta, (e) Crystal ofanhydrite in ash, (f) Section in bread crust bomb: phenocrysts of plagioclase (Pl) and pyroxenes (Px) in glass with microlites
of plagioclase.

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Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

Figure 3. X-ray microdiffraction of (a) PAP-06 (assemblage3) and (b) ash-1. Mineral abbreviation: Al= Natroalunite;
An= Anhydrite; Cr= Cristobalite; Po= Pyrophyllite; Py=
Pyrite; Qz= Quartz.

Figure 4. X-ray microdiffraction of (a) PAP-03 (assemblage4) and (b) ash-2. Mineral abbreviations: C= Opal; Ka=
Kaolinite; Ma= Marcasite.

to 91°C and TDS concentrations between 1350 to5660 mg/l. Mud-pools differing greatly from thetwo groups of springs, have low pH (0.3 and 1.1),
temperatures close to boiling (87 to 95°C) and high
TDS concentration (2860 to 41610 mg/l). Thesetypes of water are highly enriched in Boron due tothe strong evaporation of the pools.

shown on Figure 5. The St/HCl ratio of the gases
vary, while the CO2/St ratios remain constant. Thesevariations are probably caused by a selective absorption of more soluble water species, H2S, SO2 andHCl, by the hydrothermal water and re-equilibrationof magmatic gases at a low temperature (<400°C).
To conﬁrm the origin of the volcanic gases, the hydrogen (D/H) and oxygen (18O/16O) isotopic ratios
for the Papandayan gases and hot springs (Tables 3
and 4) are compared (Figure 6) with the compositions of local meteoric water and high temperaturegases from volcanic arc magmas (Taran et al., 1989;
Giggenbach, 1992). The local meteoric water line

DISCUSSIONS
Chemical Composition of Gases
Relative concentrations of HCl, St and CO2 are

Table 2. Chemical Composition (μ.mol.mol-1) and Isotopic (0/00) of Volcanic Gases and Temperature (C). (From (a) Giggenbach(1996), (b) Giggenbach et al. (2001), and (c) Fisher (pers.com))
Sample

date

Temp.

H20

CO2

H 2S

SO2

St

HCl

H2

HF

N2

O2

CH4

CO

δ18O

δD

réf.

gaz1

-

400

960000

29400

2900

6750

9650

1250

140

33

550

<20

0.6

0.3

-

-

(a)

gaz2

23/07/1994

282

965000

24900

7010

1490

9030

-

-

-

-

-

-

-

-

-

(b)

gs1

12/07/1995

360

949530

36042

7935

2563

10498

1846

268

99

1687

28

0.9

<0.04

4.6

-31

(c)

gs2

14/07/1995

148971570

20560

5354

1029

6383

1073

72

13

324

<7

0.4

<0.02

2.8

-35

(c)

gs3

14/07/1995

170969730

25398

4052

319

4371

15

17

14

440

<9

2.3

<0.003

-3.5

-54

(c)

gs4

14/07/1995

99989770

14406

2266

<100

2070

317

22

0.7

415

<5

0.7

<0.001

0.1

-41

(c)

gs5

14/07/1995

150

971150

20734

4419

805

5224

<2400

70

7.6

389

<7

0.7

<0.002

3.5

-32

(c)

gs6

16/07/1995

280

977170

16142

3931

1169

5100

1109

53

26

377

<7

0.4

<0.002

4.5

-32

(c)

gs7

16/07/1995

100

962400

29785

5570

1387

6957

<280

17

2.8

543

12

0.4

<0.004

1.3

-41

(c)

gs8

18/07/1996

300

967880

23469

5819

1198

7017

918

310

25

368

<12

1.2

0.004

4

-36

(c)

gs9

18/07/1996

128973900

18418

4647

1133

5780

1639

8.7

22

229

<6

0.6

0.002

3.1

-34

(c)

gs10

18/07/1996

103971620

23550

4034

401

4435

17

14

0.4

353

<9

0.2

<0.003

-3.3

-53

(c)

gs11

22/07/1996

138963230

28315

6058

1578

7636

<370

76

5.1

357

<10

3.0

<0.004

2.5

-35

(c)

gs12

22/07/1996

160

964050

25666

6146

2032

8178

1466

270

4.9

361

<13

1.1

0.004

3.2

-39

(c)

gs13

22/07/1996

96969160

25041

4931

399

5330

<16

9.2

0.9

432

<10

1.0

0.003

-0.7

-49

(c)

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)21

Table 3. Chemical (mg.kg-1) and Isotopic Compositions of Waters from the Papandayan Volcano
Sample

Date

K

Ca

Mg

Si

B

Mn

Al

FeTot

Fe2+

F

Cl

SO4

H2S

TDS SO4/Cl Mg/Cl

Δ18O of δD of
δ34SSO4
Water Water
(‰)
(‰)
(‰)

24
21
20
21
28
28
16
48
28
37
29
26
14
26
22
14
22
24
74
42
30
56
84
86
56
120
80
47
17
113
55
140

11
10
17
10
21
22
9
20
15
24
18
22
11
18
19
8
21
25
17
16
7
20
26
19
22
20
22
10
6
15
20
23

33
35
28
28
32
26
23
73
45
52
38
37
25
31
33
25
26
33
550
498
99
97
209
338
101
234
437
336
84
134
111
284

13
12
11
11
11
12
9
27
14
18
14
13
10
12
14
9
11
10
134
44
20
38
92
112
41
122
123
122
22
48
46
170

73
108
111
80
145
93
76
245
166
220
151
169
70
136
112
115
105
154
99
180
51
77
162
104
86
147
97
75
41
178
97
155

2.2
1.2
4.1
1.7
4.0
1.6
1.5
7.3
4.1
4.2
3.1
4.7
1.7
2.1
7.2
1.9
2.4
5.3
3.8
1.2
1.1
7.4
17.1
-

0.6
0.5
0.4
0.4
0.4
0.3
0.3
1.4
0.8
1.0
0.7
0.6
0.3
0.4
0.5
0.3
0.3
0.4
21.8
11.0
2.3
1.6
6.3
1.5
2
9
2.2
6.1
3
-

31
49
91
17
141
33
16
146
80
107
57
114
21
45
86
25
53
160
396
7.2
6.5
10
172
211
4
79
131
153
0.22
16
4
106

0.4
2.8
4.5
0.4
8.7
4.1
0.8
21
8.0
13
7.0
6.5
0.2
3.3
10
0.3
2.8
7.3
854
22
1.0
28
561
473
44
798
427
668
0.32
62
60
1010

18
8
13
8
9
0.3
8
6
-

4
4
11
3
13
4
4
17
11
11
8
11
3.4
5
8
3.9
6
<10
8
<8
<4
<10
4.5
<20
<5
<10
6.9
<10
<5
9
4
20

216
183
747
163
1186
198
159
981
566
606
380
919
190
364
1420
213
384
1422
679
198
46
185
1192
298
149
639
308
539
25
93
142
631

222
404
481
215
509
364
191
867
518
605
427
417
200
291
531
174
295
790
5544
1449
359
393
2769
2962
433
3090
3042
3123
286
1187
513
4386

0
3
0
0.2
-

631
830
1526
551
2099
787
506
2453
1457
1698
1122
1741
547
935
2263
590
928
2630
8380
2469
623
835
5134
4513
852
5111
4599
5058
443
1676
954
6750

1.0
2.2
0.6
1.3
0.4
1.8
1.2
0.9
0.9
1.0
1.1
0.5
1.1
0.8
0.4
0.8
0.8
0.6
8
7
8
2
2
10
3
5
10
6
11
13
4
7

0.06
0.07
0.01
0.07
0.01
0.06
0.06
0.03
0.03
0.03
0.04
0.01
0.05
0.03
0.01
0.04
0.03
0.01
0.2
0.2
0.4
0.2
0.1
0.4
0.3
0.2
0.4
0.2
0.9
0.5
0.3
0.3

9.5
10.3
8.7
9
14.5
9.5
17
1.4
7.3
0.4
2.0
3.5
6.4
-0.3

-7.3
-7.1
-7.2
-6.7
-7.6
-

-56
-53
-54
-56.5
-55.5
-

98
26
13

35
8
4

645
481
367

125
60
38

116
40
30

7.4
-

19.4
9
-

44
67
85

44
176
219

49
-

<10
<10
<10

580
108
60

2241
2142
2086

16
-

3839
3078
2873

4
20
35

0.2
0.6
0.6

6.0
4.8
2.9

-

-

1.2
2.5
2.4
1.7
1.8
2.1
1.9
2.6

34
41
47
28
18
19
14
43

23
8
22
7
8
6
5
9

70
177
550
79
85
76
62
96

31
77
84
52
29
42
16
28

75
161
193
154
138
152
150
153

0.3
1.6
0.6
-

1.7
4.0
2.9
2
0.89
-

313
81
249
241
160
234
93
23

248
556
220
204
69
250
19
130

-

5.3
<10
<16
<10
0
3
2
<5

27
14
15
24
<5
10
4
8

4905
2886
4012
3839
2201
2656
1579
1011

45
18
-

5658
3845
5202
4575
2570
3296
1794
1347

182
206
269
161
263
367
135

1.2
5.5
5.6
2.2
4.2
3.7
3.7

-0.99
1.8
4.5
1.8
3.4
-

-

-

0.4
1.1
0.3
0.8
0.9
0.6

35
22
77
3
3
7
26
16
54
4
8
7
6
6
12
362 141 1432

32
4
24
5
6
643

177
169
140
165
150
214

500
3.6
100
8.4
11.4
-

2.3
0.2
1.1
0.2
0.3
26

250
63
99
80
89
5020

110
33
36
37
36
1871

-

212
6.5
45
9.4
1.2
21

26797
1520
26771
2858
4443
26963

1107
1215
1256
1644
2272
5134

12

29145
2857
28428
4661
6883
41613

0.04
0.08
0.05
0.58
0.51
0.19

0.001
0.003
0.001
0.002
0.001
0.024

-

-

-

Temp pH
Na(0C) meas

Acid sulphate-chloride waters
Pap1
Jul.9463
2.5
Pap2
Jul.9455
2.5
Pap3
Jul.9480
1.9
Pap5 23/08/1998 75
2.3
Pap6 23/08/1998 93
1.6
Pap7 23/08/1998 70
2.2
Pap8 23/08/1998 71
2.5
Pap9 05/02/2000 88
1.7
Pap10 05/02/2000 92
1.9
Pap11 05/02/2000 86
1.9
Pap12 05/02/2000 63
2.0
Pap9 31/07/2001 94
1.7
Pap13 31/07/2001 66
2.4
Pap12 31/07/2001 69
2.1
Pap14 14/09/2002 91
1.5
Pap13 14/09/2002 64
2.4
Pap12 14/09/2002 66
2.2
Pap13 14/09/2002 90
1.7
Pap15 29/01/2003 45
2.6
Pap16 29/01/2003 17
3.1
Pap17 31/01/2003 40
3.8
Pap18 29/06/2003 75
3.3
Pap19 30/06/2003 88
1.9
Pap20 23/07/2004 48
2.6
Pap18 23/07/2004 82
3.2
Pap19 23/07/2004 85
1.9
Pap21 24/07/2004 49
2.4
Pap22 24/07/2004 92
2.6
Pap17 16/08/2004 36
4.6
Pap23 30/07/2005 86
2.3
Pap18 30/07/2005 86
3.2
Pap19 30/07/2005 84
1.9
Crater lake
Pap24 27/06/2003 50
3.2
Pap24 23/07/2004 42
2.7
Pap24 30/07/2005 37
2.7
Acid sulphate waters
Pap25 05/02/2000 23
Pap26 27/06/2003 92
Pap27 27/06/2003 45
Pap26 2307/2004 91
Pap27 23/07/2004 52
Pap26 30/07/2005 82
Pap27 30/07/2005 79
Pap28 3007/2005 94
Sulfur-mud pools
Pap29 05/02/2000 88
Pap30 05/02/2000 87
Pap31 31/07/2001 95
Pap30 31/07/2001 89
Pap30 14/09/2002 Pap32 24/07/2004 90(LMWL) was constructed from the GNIP data covering the period 1962-1997 for Indonesia (Jakarta station). The isotopic compositions of the Papandayan
fumaroles lie on a mixing line between “magmatic
end member” and local meteoric water. The water
discharges are dominated by meteoric waters witha minor magmatic contribution. The δ18O valuesof gases close to the local meteoric waterline areshifted by ~4 ‰ from the hot springs δ18O values.
A similar shift has been observed in fumaroles from
Kudryavy volcano (Taran et al., 1995) and Galeras(Fischer et al., 1997). These autors attributed thisshift to an interaction between meteoric water andmagmatic gases leading to enrichment in δ18O of
the vapor phase. The same process may be present
at the Papandayan Volcano.

Changes in the Chemistry of Thermal Water
after the Eruption
Different processes which can occur between thecooling magma at depth and the hot springs at thesurface are as follows: injection of magmatic gases
into the hydrothermal system, dissolution of rock by
the acid ﬂuids and dilution of acid ﬂuids by meteoric
water. On Figure 7, a positive correlation between
Cl and hydrogen ion activity (10-pH) is shown. The
increase in Cl- is concomitant with the more H+
value. The correlation indicates that the Cl in thesprings was supplied in the form of HCl solution orvapor. Furthermore, the concentrations in F, Cl andSO4 in the acid chloride-sulphate water reﬂect aninjection of magmatic gases (SO2, H2S, HCl, HF)
in to the hydrothermal system.

22

Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

Table 4. Average Chemical Composition of Andesite
SiO2
(wt%)

Al2O3
(wt%)

Fe2O3
(wt%)

MnO
(wt%)

MgO
(wt%)

CaO
(wt%)

Na2O
(wt%)

K 2O
(wt%)

57.27

18.52

7.49

0.13

3.03

7.10

2.80

1.38

The chemistry of samples collected two months
before the November 2002 eruption show no detectable changes, suggesting that no signiﬁcantmodiﬁcation occurred in the pre-eruptive degassing.
The chemistry of samples collected after the eruption reveals however notable changes. The mostsigniﬁcant changes are an increase in SO4/Cl and
Mg/Cl ratios (Figure 8, Table 3). This could be dueto the intrusion of a fresh magma at shallow depth(Giggenbach, 1974; Pasternack and Varekamp,
1994). The acid sulphate water that are likely to havebeen generated at subsurface show the same increasein Mg/Cl ratio than the acid chloride-sulphate water.
A more likely explanation for the changes observedin the 2003 data is the opening of new fractures
where unaltered or less altered volcanic rocks werebrought in contact with the ascending acid water. To
conﬁrm this hypothesis, we evaluated the degree ofwater-rock interaction was evaluated by calculating
the percentage of residual acidity (PRA) recently
introduced by Varekamp and Kreulen (2000) for
crater lake studies. The PRA is deﬁned as the residual acidity left after the neutralization of a ﬂuid

Figure 6. Oxygen and hydrogen isotopic compositions of the
Papandayan gases, hot springs and meteoric water. LMWL
is local meteoric line.

Figure 7. Cl versus H+ activity of the Papandayan hot
springs.

Figure 5. HCl-CO2-St concentrations in fumarolic gases of
the Papandayan Volcano.

by water-rock (WR) interaction. Since acidity isconsumed by hydrolysis reaction during WR interaction, PRA is independent of dilution or boiling. The
pure acid or initial acidity was computed for eachsample from their Cl and SO4 concentrations with
PHREEQC. The graph 100 × Mg / (∑ RFE) versus
residual acidity is shown on Figure 9, corresponds
to the easily leached element Mg on a molar basis
relative to the sum of major rock forming elements(RFE = Na + K + Mg + Ca + Al). The data show a
net decrease in the residual acidity for the sampledcollected in 2003-2005 accompanied by an increasein the relative Mg concentration. This trend reﬂects
an increase in the neutralization of the acid springsand show that the WR interactions were more signiﬁcant after the eruption.

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)23

Figure 9. Plot of the percentage of residual acidity versus
100 x Mg/ERFE (Sum of major rock-forming elements)=
Na+Ca+Mg+K+Al+Fe.

Figure 8. Cl concentration versus SO4 and Mg concentrationsof water sampled before (1994-2002) and after the eruption(2003-2005).

Sulphur Isotopic Composition
Figure 10 shows δ34S of sulphates versus the
SO4 weight fraction 100 × cSO4 / (cSO4 + cCl). The
high δ34S values (9-17 ‰) observed in acid sulphatechloride water before the November 2002 eruption
strongly indicates that dissolve sulphates are mainly
formed from the disproportionation of magmatic
SO2 (Ohmoto and Goldhaber, 1997; Kusakabe etal., 2000) according to thereaction of: 4SO2 + 4H2O+
→ 3HSO+ H2S + 3H or 3SO2 + 3H2O → 2HSO4
4
0+ S + 2H. Kusakabe et al. (1992) show that thedisproportionation of SO2 leads to a large isotopic
fractionation between dissolved sulphates and H2Sor elemental sulphur. The low δ34S of sulphates in
the chloride-depleted water collected before theeruption indicates that the origin of sulphates for thiswater is the surﬁcial oxydation of hydrogen sulphide(Kiyosu and Kurahashi, 1983). This Cl-depleted
water has been formed from the condensation of
steam rising from the boiling hydrothermal system

Figure 10. Plot of δ34S SO4 versus 100xcSO4/ (cSO4+cCl) of
hotsprings from the Papandayan Volcano. Ci= Concentrationof element I in mg/kg.

to the subsurface above the water table (Reed andSpycher, 1985). The water samples collected after
the eruption show low values of δ34S of dissolved
sulphates (7 to -0.3‰). This indicates that there was
no increase in the contribution of magmatic ﬂuids inthe upper part of the hydrothermal system.
Crater Lake
Water from the new crater lake have been collected since 2003. An evolution in the SO4/Cl ratio
is observed during 2003-2005 showing a decrease in
Cl content, whereas SO4 value remains stable (Table

24

Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

4). The low values of δ34S (3-6 ‰) for sulphates ofthe lake water indicates that the origin of these sulphates may be the result of H2S surﬁcial oxidationand not the disproportionation of SO2. The lake waterreﬂects the hydrothermal ﬂuids present at depth witha magmatic contribution less important with time.
Cation concentrations have decreased since 2003,
but the residual acidity increased slightly (Figure 9).
This indicates a decrease in water-rock interaction
or a contact between acid waters and wall rock has
already completely leached.
Water-rock Interaction
A relationship between rock forming elements(RFE) concentrations and their abundance in volcanic rocks from sample data collected before theNovember 2002 eruption is presented in Figure 11.
An average composition of 4 samples of andesite
reported is used for the comparison (Table 4). A
congruent dissolution is observed with thermal
water and corresponds to 1g of andesite per kg ofacid waters. This water is depleted in Si, Al, andFe compared to their rock abundance. The solubility of Si decreases with a decrease in temperature(Nicholson, 1993). Aluminium is strongly negatively
correlated with the pH, where solubility of Al decrease with an increase in pH and can co-precipitateswith Si. The iron is highly depleted compared to its
rock abundance. Fe solubility is pH dependent but
this can not explain the very low concentrations inwater. However, abundant pyrites have been foundin the ashes and altered rocks. Therefore, Fe could
be consumed in the reaction that formed pyrite. In
experimental studies (Schoonen and Barnes, 1991)
two steps of formation of pyrite and marcasite has
been described. The ﬁrst step is the precipitation ofiron monosulphide (FeS) by the reaction:
Fe2+ + H2S (aq) → FeS (s) + 2 H+
In the second step, iron monosulphide is converted to an iron disulphide either(1) Fe loss:
2FeS(s) + 2H+ → FeS2(s) + Fe2++ H2(g)or(2) sulphidation:
FeS(s) +H2S(aq) → FeS2(s) + H2(g)orFeS(s) + HS (aq) + H- 2O(l) → FeS2(s) +H2(g) + OH
Iron disulphides are formed most readily if thesolutions contain an excess of thiosulphates, poly-

Figure 11. Concentration of rock forming elements (RFE) in lake water compared to the Papandayan andesite.

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)thionates and/or polysulphides.
Congruent dissolution of rock has been reported
by Bernard et al. (2004) for Santa-Ana Crater Lakeand by Ohba (1994) for Yugama Crater Lake as themain source of RFE in water. However, other processes can affect the concentration of RFE in crater
lakes. The dissolution of lava rock by magmatic
volatiles leads to leaching different rates for theRFE (Christenson and Wood, 1993; Varekamp andKreulen, 2000). The incongruent dissolution can be
explained also by the precipitation or dissolutionof minerals in lake water or in the hydrothermal
system depending on the temperature and chemical
ﬂuctuations of acid ﬂuids injected in to the system(Delmelle and Bernard, 1994; Christenson andWood, 1993). The congruent dissolution of RFE
at the Papandayan Volcano may be explained by alarge circulation of thermal water in the subsurface

25

system. However, the assemblages of alteration
minerals found in the ejectas show that an interaction
between acid ﬂuids and non-altered lava rocks (orless altered) occurs. So, a precipitation of minerals
and neutralization of ﬂuids took place in the hydrothermal system (Giggenbach, 1992; Hedenquist etal., 1994; Reyes, 1990).
To improve our knowledge about the water-rockinteraction in the system, a model is used on thebasis of the stability of pyrophyllite, kaolinite andalunite as a function of log SiO2, aq and pH (ﬁgure12). The code SUPCRT92 (Johnson et al., 1992)
was used to compute the thermodynamic constantneeded to build the stability ﬁeld diagram. Quartz is
assumed to be oversaturated in the model, because
this phase is largely present in the altered rocks. The
limits of stability reported on Figures 12a, b, c, andd correspond to the ﬂuids Pap-2 (higher pH = 2.5)

Figure 12. Stability diagram of pH versus log aSiO2, aq of the acid sulphate-chloride alteration phases from 150oC to 300oC.
The dotted line corresponds to the saturation of silica.

26

Jurnal Geologi Indonesia, Vol. 2 No. 1 Maret 2007: 15-29

and Pap-14 (lower pH=1.5) at different temperatureand computed with PHREEQC (Parkhurst and Appelo, 1999) by using the thermodynamic database
Wateq4f (Ball and Nordstrom, 1991). In Figure 12,
the range in pH measured in the ﬂuids and calculated
at different temperatures is also indicated by arrows
on the diagram. In the stability diagrams (Figures
12c and d), pyrophyllite and kaolinite coexist at
250°C. Experimental studies by Hemley et al.(1980)
show that kaolinite and pyrophyllite can coexist at
temperature about 270°C at quartz saturation. The
presence of kaolinite is pH dependent and for waterwith pH below 2 and temperature of 250°C, kaolinite
is no more stable. Pyrophyllite is a mineral that may
form at high temperature in geothermal systems(Reyes, 1990; Nogami et al., 2000; Hedenquist etal., 1998), in many ore deposits districts (Marumo,

1989; Hedenquist et al., 1994; Yilmaz, 2003) andon active volcanic sites (Christenson and Wood,
1993; Nogami et al., 2000). Alunite can also coexist
with kaolinite and pyrophyllite between 250-300°C(Hedenquist et al., 1998). For the ﬂuids studied,alunite is a stable phase between 200 and 150°C.
To specify the temperature of formation of alunite, another stability diagram was used (Stoffregenet al., 2000; Figure 13). In this diagram, stabilitiesof alunite, kaolinite/pyrophyllite and muscovite
were plotted versus H+-SO42- activities and K+SO42activities. Silica is ﬁxed by the quartz saturation.
On Figure 13, equilibrium compositions of ﬂuids
calculated at different temperatures are also plotted.
Alunite appears at temperatures below 300°C andthis is the Al-bearing phase stable at temperatures
below 150 °C (Figure 13).

Figure 13. Stability diagram of log (a2H+ x aSO42-) versus -log (a2K+ x aSO42-) of the muscovite, pyrophyllite, and alunite
phases from 150oC to 300oC. Data from the Papandayan water is also reported on the diagram.

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistryevolution of thermal water after the November 2002 eruption (A. Mazot, et al.)CONCLUSIONSThe chemical and isotopic compositions of acidhot springs from the crater of THE Papandayan
Volcano sampled since 1994 indicate that a contribution of magmatic volatiles (HCl, SO2, H2S, HF)
to the hydrothermal system is likely present andthat interaction between acid ﬂuids and rocks took
place. The altered mineral assemblages identiﬁed in
the rocks ejected during the November 2002 eruption and coming from the hydrothermal system is atypical of an advanced argillic alteration.
The eruption produced notable changes in thechemistry of the hot springs. Most of these chemical changes can be related to a modiﬁcation in the
dynamic circulation of these ﬂuids to the surface
by the opening of new fractures. Furthermore, noevidence of intrusion of fresh magma in the upper
part of the hydrothermal system has been found. The
hydrothermal zones are likely restrained to faults
or permeability structure (Reyes, 1990; Stoffregen,1987). The acid ﬂuids could ascend to the surface
and lead to the formation of hot springs or descendalong the structures to deep level and react withthe host rock. This interpretation may explain why
closely different ﬂuids can cause different type ofadvanced argillic alterations.
The chemical monitoring at the Papandayan Volcano is a useful tool for understanding the processes
in the hydrothermal system and to survey the levelof activity, especially after the phreatic eruption likethat in November 2002 which was able to be follow
by a magmatic eruption.
Acknowledgments---This work was ﬁnancially supportedby the “Centre de Recherches Volcanologiques” (CRVOPGC, University Blaise Pascal), in France and the
Comunauté Française in Belgium. We are very grateful tothe directors of the Volcanology and Geological Hazard
Mitigation (DVGHM), in Indonesia, Wirakusumah andSiagian to their cooperation. We thank also our colleaguesof DVGHM for their participation in ﬁeld campaigns.

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