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  • Indonesia
  • Indonesia
  • Caldera
  • Unknown - Uncertain Evidence
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 4.83°S
  • 103.92°E

  • 1881 m
    6170 ft

  • 261251
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Ranau.

The Global Volcanism Program has no Weekly Reports available for Ranau.

Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

04/2011 (BGVN 36:04) Fish kill in April 2011 strikes hot-spring areas of intra-caldera lake

Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

04/2011 (BGVN 36:04) Fish kill in April 2011 strikes hot-spring areas of intra-caldera lake

This, our first report on Ranau, a Pleistocene caldera that lies along the Great Sumatran fault, is based on accounts of fish kills, including one on 4 April 2011. The fish died near hot springs in Lake Ranau, a large caldera lake, and their deaths were attributed to seismically induced H2S releases by the Center of Volcanology and Geological Hazard Mitigation (CVGHM). CVGHM reported the surface area of Lake Ranau to be ~127 km2, and noted that the Lake Ranau complex is geothermally active, with hot springs that emerge at the foot of Mount Seminung on the banks of Lake Ranau.

In addition to the 2011 event, fish kills have been recorded in Lake Ranau (figure 1) for the past five decades (table 1).

Table 1. Previous fish kills in Lake Ranau reported during the past five decades. (Note that there is no mention of any correlation between seismicity and geochemical anomalies.) Courtesy of CVGHM.

Year Description
1962 According to informants in Sende Simpang Village, both the lake water became milky white in color and all of the fish died.
1993 During a sequence lasting 3 months, one or more fish kills occurred.
1995 A small-scale fish kill occurred, accompanied by a rotten smell (presumably H2S).
1998 According to reports, a large-scale fish kill occurred, in which all of the fish died. According to the head of the village, Sugih Sane, the event began with turbulent water in Lake Ranau that lasted for approximately 30 minutes.
Figure 1. Photo of Lake Ranau with Mount Seminung in the background. Posted by blogger "masternewstoday" in May 2011.

Reports stated that the 4 April 2011 fish kill was large in scale. According to the head of a nearby village, Sugih Sane, the event began with turbulent water in Lake Ranau that lasted for approximately 30 minutes.

Local residents reported that the recent fish kill occurred during a relatively short time on 4 April 2011, in portions of the lake surrounding hot springs. At the time of the incident, the water in the affected areas appeared milky white, and wind spread the smell of sulfur to surrounding areas.

Geochemistry. Scientists conducted field work near the three hot springs Kota Batu, Ujung, and Way Wahid during 16-19 April 2011. At that time they reported the following:

* No dead algae were found on the lake's surface.

* There was no smell of sulfur, the water was clear, and the water around the hot springs was bubbling and warm. * Dead fish were no longer present.

* The pH of the lake water was 7.74, and the temperature was 26.1°C. The water near the hot springs had a pH of 6.32-7.06, with a temperature of 47.8-62°C. The water of the river that empties into Lake Ranau (input) had a pH of 8.07-8.10, and the lake water discharge (output) had a pH of 7.86.

* The result of ambient gas examination showed no gases associated with magmatic gases, such as CH4, CO2, CO, and H2S, in the vicinity of the hot springs discharge.

The degree to which the above measurements were anomalous was unstated.

Seismicity. CVGHM reported that seismic data recorded during 16-20 April 2011 showed microearthquake activity around Lake Ranau. The earthquakes were located along a fault line oriented in the SE-NW direction along Lake Ranau, at depths of 0.6 and 10 km below the surface of the lake. The Berkelulusan location coincides with the location of the Kota Batu hot springs.

Prior to the fish kill at Lake Ranau on 4 April, an M 5.1 earthquake was recorded on 29 March 2011 in Bengkulu, ~160 km W of Lake Ranau.

Cause. CVGHM concluded that, based on the results of the field work (location of dead fish near hot springs, sulfur smell carried by wind up to 3 km away, absence of dead algae, and changing color of the lake water to milky white during the event), the fish kill in Lake Ranau was caused by the release of H2S gas into the lake water, which caused imbalances in lake water chemistry.

CVGHM said that hydrothermal gas was trapped over time and escaped to the surface after the pressure due to tectonic disturbances. CVGHM concluded that the M 5.1 earthquake in Bengkulu on 29 March 2011 led to increased pressure on the fault in the vicinity of Lake Ranau; then, H2S gas was released to the surface in the vicinity of the hot springs.

CVGHM reported that the occurrence of microearthquakes is a result of the fault in the vicinity of Lake Ranau, and are neither dangerous nor destructive. However, CVGHM asked residents to report future fish kills to the local government.

An essay by Kibria (2011) discusses a wide variety of fish kills in the global context and notes cases with H2S as the probable cause.

Reference. Kibria, G., 2011, Global fish kills: Causes and consequences, Science and Technology Article 21, URL: http://www.sydneybashi-bangla.com (February 2011, 2 pp.).

Information Contact: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/); Masternewstoday (URL: http://hot-breaking-news-masternewstoday.blogspot.com).

Ranau is an 8 x 13 km Pleistocene caldera partially filled by the crescent-shaped Lake Ranau. The caldera lies along the Great Sumatran Fault that extends the length of Sumatra. Incremental formation of the caldera culminated in the eruption of the voluminous Ranau Tuff about 0.55 million years ago. A morphologically young post-caldera stratovolcano, Gunung Semuning, was constructed within the SE side of the caldera to a height of more than 1600 m above the caldera lake surface. The volcano has not been mapped in sufficient detail to determine the age of its latest eruptions, although fish kills and sulfur smells in the late 19th and early 20th centuries may be related to sublacustral eruptions.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1903 Dec 9 ] [ 1903 Dec 9 ] Uncertain    
[ 1887 Oct 7 ] [ 1888 Jan 20 ] Uncertain    

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Feature Name Feature Type Elevation Latitude Longitude
Seminung, Gunung
Stratovolcano 1881 m 4° 55' 0" S 103° 58' 0" E
Crescent-shaped Lake Ranau partially fills the 8 x 13 km Ranau caldera. A morphologically young post-caldera stratovolcano, Gunung Semuning, its summit capped by clouds below the bottom center lake shore in this NASA Landsat image (with north to the top), was constructed within the SE side of the caldera to a height of more than 1600 m above the caldera lake surface. The age of the most recent eruptions at Ranau are not known, but fish kills and sulfur smells in the late 19th and early 20th centuries may be related to sublacustral eruptions.

NASA Landsat7 image (worldwind.arc.nasa.gov)

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Bellier O, Bellon H, Sebrier M, Sutanto, Maury R C, 1999. K-Ar age of the Ranau Tuffs: implications for the Ranau caldera emplacement and slip-partitioning in Sumatra (Indonesia). Tectonophysics, 312: 347-359.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Latter J H, 1975b. The history and geography of active and dormant volcanoes. A worldwide catalogue and index of active and potentially active volcanoes, with an outline of their eruptions.. Unpublished manuscript, unpaginated.

Newhall C G, Dzurisin D, 1988. Historical unrest at large calderas of the world. U S Geol Surv Bull, 1855: 1108 p, 2 vol.

Volcano Types


Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Andesite / Basaltic Andesite


Within 5 km
Within 10 km
Within 30 km
Within 100 km

Affiliated Databases

Large Eruptions of Ranau Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.