Report on Suoh (Indonesia) — May 1994
Bulletin of the Global Volcanism Network, vol. 19, no. 5 (May 1994)
Managing Editor: Richard Wunderman.
Suoh (Indonesia) Water chemistry of the boiling, post-eruption hot-springs
Please cite this report as:
Global Volcanism Program, 1994. Report on Suoh (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 19:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199405-261270
Suoh
Indonesia
5.25°S, 104.27°E; summit elev. 1000 m
All times are local (unless otherwise noted)
A . . . small eruption at Suoh hot-spring field that expelled gas-charged hot mud [followed] a major, destructive earthquake in the same region (19:02). The earthquake, Ms 7.2, took place at 1707 GMT on 15 February, or in terms of local time and date, at 0007 on 16 February.
"We sent our team to investigate the area where the phreatic explosion occurred. The team arrived at Suoh on 19 February, three days after the earthquake. Two new mud explosion pits, 5 m in diameter, were found W of the Suoh depression. Liquifaction was consistently found at fractures associated with the earthquake. The two explosion pits contained boiling water."
Tables 1 and 2 present data on water and gas samples taken from two sites in the Suoh area during the investigation.
Table 1. Water chemical analyses for two sites in the Suoh hot-spring field (sampled 19 February 1994). Courtesy of VSI.
| Measured Parameter | Hot Spring | Crater Lake |
| Temperature (°C) | 97.6 | 33.0 |
| pH | 8.12 | 3.09 |
| Conductivity (µS/cm) | 883 | 967 |
| Na+ ppm | 299 | 199 |
| K+ ppm | 20.8 | 28.4 |
| Li+ ppm | 2.21 | 2.67 |
| Ca+2 ppm | 12.1 | 8.33 |
| Mg+2 ppm | 4.7 | 6.07 |
| Fe+3 ppm | 0.00 | 1.27 |
| Mn+2 ppm | 0.00 | 0.00 |
| As+3 ppm | 192 | 0.005 |
| SiO2 ppm | 18.4 | 207 |
| Boron ppm | 604 | 7.2 |
| Cl- ppm | 175 | 308 |
| SO4 ppm | 713 | 86.5 |
| HCO2-3 ppm | 0.50 | -- |
| F- ppm | 0.40 | 0.25 |
| NH3 ppm | -- | 0.01 |
Table 2. Gas chemical analyses for two sites in the Suoh hot-spring field (sampled 19 February 1994). Courtesy of VSI.
| Element | Suoh (TB-1), Kawah Api Porwarnas | New explosion pit (Kawah Baru) | ||
| Total Gas (mole %) | Dry Gas (mole %) | Total Gas (mole %) | Dry Gas (mole %) | |
| H2 | 0.003 | 0.89 | 0.005 | 0.25 |
| O2+Ar | 0.040 | 11.9 | 0.070 | 3.44 |
| N2 | 0.180 | 53.4 | 0.120 | 59.4 |
| CO | 0.002 | 0.59 | 0 | 0 |
| CO2 | 0.100 | 29.7 | 0.480 | 23.6 |
| SO2 | 0.001 | 0.30 | 0.250 | 12.3 |
| H2S | 0.004 | 1.19 | 0.020 | 0.98 |
| HCl | 0.007 | 2.08 | 0.002 | 0.098 |
| H2O | 99.66 | -- | 97.96 | -- |
Geological Summary. The 8 x 16 km Suoh (or Suwoh) depression appears to have a dominantly tectonic origin, but contains a smaller complex of overlapping calderas oriented NNE-SSW. Historically active maars and silicic domes lie along the margins of the depression, which falls along the Great Sumatran Fault that extends the length of the island. Numerous hot springs occur along faults within the depression, which contains the Pematang Bata fumarole field. Large phreatic explosions (0.2 km2 tephra) occurred at the time of a major tectonic earthquake in 1933. Very minor hydrothermal explosions produced two 5-m-wide craters at the time of a February 1994 earthquake.
Information Contacts: R. Sukhyar, VSI.
