VOLCANOES IN INDONESIA

VOLCANOES IN INDONESIA

Many of Indonesia’s islands are rugged remnants of extinct volcanoes. There are around 400 volcanoes in Indonesia, A string of volcanoes runs all the way from Sumatra to Flores with more in Sulawesi and The Moluccas. Of these 127 are active, about a third of all the world's active volcanoes. Indonesia is one of the most geologically active regions in the world. On average there are three earthquakes a day, measuring 5 or more on the Richter scale. There are about 10 times as many deaths from volcanic eruptions in Indonesia as in there are in any other country.

On the positive side, volcanic lava and ash produces rich soil that can produce multiple harvest year after year without fertilizer. High volcanic peaks can generate rain. Andrew Marshall of Associated Press wrote: In Indonesia, volcanoes are not just a fact of life, they are life itself. Volcanic ash enriches the soil; farmers on Java can harvest three crops of rice in a season. Farmers on neighboring Borneo, with only one volcano, can't. [Source: Andrew Marshall, Associated Press, January 2008 <>]

There are76 historically active volcanoes, more than any other country. As of 2006, according to The Guardian, Indonesia had a total of 1,171 eruptions, narrowly beaten by Japan's 1,274 Well-known active volcanoes include are 2,968-meter-high Mount Merapi (Gunung Merapi), in Jawa Tengah Province, which last erupted in 2007, and Soputan, in Sulawesi Utara Province, which last erupted in 2008. Between 1972 and 1991, twenty-nine volcanic eruptions were recorded, mostly on Java. Between 2000 and 2009, 110 new or continuous volcanic eruptions were recorded in Indonesia, mostly in Java. [Source: The Guardian, Library of Congress *]

Significant volcanic activity occurs on Java, Sumatra, the Sunda Islands, Halmahera Island, Sulawesi Island, Sangihe Island, and in the Banda Sea; Merapi has been deemed a Decade Volcano by the International Association of Volcanology and Chemistry of the Earth's Interior, worthy of study due to its explosive history and close proximity to human populations; other notable historically active volcanoes include Agung, Awu, Karangetang, Krakatau (Krakatoa), Makian, Raung, and Tambora. *

The most violent geologic events in modern times have occurred in Indonesia: In 1815 the explosion of Mount Tambora (Gunung Tambora), a massive volcano in Nusa Tenggara Barat Province on the island of Sumbawa, reportedly killed an estimated 60,000 people and created "the year without a summer" in various parts of the world. It last erupted in 1967. Krakatau, a volcano situated on an island between Java and Sumatra, erupted in 1883, and more than 36,000 died in the resulting tsunamis, which were felt as far away as the Arabian Peninsula, and changes in the water level were reported as far away as Wales. The sound of the explosion was reported as far away as Turkey and Japan. For almost a century following that eruption, Krakatau was quiet, until the late 1970s, when it erupted twice. Krakatau is still active, having erupted as recently as March 2009. The Lumpur Sidoarjo (Lusi) mud volcano in Jawa Timur Province, which began in late May 2006 coincident with natural gas exploration drilling and, as some believe, an offshore earthquake, is an eruption of hydrogen sulphide gas and hot mud rather than a traditional volcano with its explosive ejections and flows of lava. [Library of Congress]

Volcanoes in Indonesia are known as gugung (“fire mountains”). They range in height from 3800-meter-high Gugung Kerinic in Sumatra to Hugung Nieuwerker, 2285 meters below the sea. The Volcanological Survey of Indonesia (Direktorat Vulkanologi) is the main organization keeping an eye on volcanoes in Indonesia. It was founded in 1920s by the Dutch and expanded by the Indonesian government. It has observation posts on some of Indonesia’s most dangerous volcanoes. Scientists monitor Merapi, Sinabung and other Indonesian volcanoes nonstop, but predicting their activity with any accuracy is all but impossible.

Indonesia continues to experience a high level of volcanic activity. In late August 2010, Mount Sinabung, near Karo, Sumatera Utara Province, erupted for the first time in 410 years, and in 2011 noteworthy eruptions occurred in Java and Sulawesi. The extended series of eruptions at Mount Merapi in late 2010 caused evacuations of more than 135,000 people and more than 300 deaths near Yogyakarta. In addition, there were earthquakes, the largest of which occurred in October 2010, when an underwater quake off the Mentawai Islands, Sumatera Barat Province, registered a magnitude of 7.7 and produced a tsunami estimated to have killed more than 300 people.

Major Volcanic Eruptions

Worst Recorded Volcanic Eruptions (number of dead): 1) Mt, Tambora, Sumbawa, Indonesia, Apr. 10-12, 1815 (92,000); 2) Krakatoa, Indonesia, Aug. 26-28, 1883 (36,000); 3) Mt. Pelée, Martinique, May 8, 1902 (28,000); 4) Nevado del Ruíz, Columbia, Nov. 13, 1985 (23,000); 5) Mt. Vesuvius, Italy, Aug 24, 79 AD (16,000); 6) Mt. Unzen, Japan, May 21, 1792 (14,500); 7) Kelud, Java, Indonesia, 1586 (10,000); 8) Laki, Iceland, June 8, 1783 (9,350); 9) Mt. Kelud, Java, Indonesia, May 19, 1919 (5,000); 10) Mt. Vesuvius, Italy, Dec. 15, 1631 (4,000); 11) Mt. Papandayan, Java, Indonesia, Aug. 12, 1772 (3,000); 12) Mt. Lamington, New Guinea, Jan 17-21, 1951, New Guinea (3,000); 13) El Chichon, Mexico, May 28, 1982 (1,800); 14) Lake Nyos, Cameroon, Aug. 21. 1986 (1,700); 15) Mt. Taal, Philippines, Jan 30. 1911; 16) Santa Maria, Guatemala, Apr. 24, 1902 (1,000); 17) Mt. Pinatubo, Luzon, Philippines, June 15, 1991 (800); 18) Mt. St. Helens, May 18, 1980 (57).

Volcanologists rank large eruptions as: Level 5) like the ones at Mount St. Helens in 1980 and Mt. Vesuvius in the A.D. 1st century that occur every 10 years and release less than a hundred cubic kilometers of material; Level 6) like the ones at Mount Pinatubo in 1991 and Krakatau in 1883 that occur every 100 years and release more than a hundred cubic kilometers of material; Level 7) like the one at Tambora in Indonesia in 1815 that occur every 1,000 years and release more than a 1,000 cubic kilometers of material; and Level 8) like the ones at Toba 750,000 years ago and Yellowstone 2.1 million years ago that occur every 50,000 to 100,000 and release 2,500 to 3,000 cubic kilometers of material. The largest volcanic event known is an eruption in Colorado 28 million years ago that released more than 5,000 cubic kilometers of material. A Level 8 is regarded as a supervolcano. The threat posed by a supervolcano is regarded as worse and ten times more likely to happen than an asteroid impact. If one were to occur today it could kill millions with the initial eruption and kill perhaps billions if a natural “nuclear winter” were triggered.

The world's dangerous volcanoes (as judged by their potential for a dangerous eruption and nearness to major population areas): 1) Merapi (Indonesia); 2) Taal (Philippines)l 3) Unzen (Japan); 4) Sakurajima (Japan); 5) Ulawun (Papua New Guinea); 6) Mauna Loa (the United States); 7) Rainier (the United States); 8) Colima (Mexico); 9) Santa Maria/ Santiaguito (Guatemala); 10) Galeras (Columbia); 11) Teide (Canary Islands); 12) Vesuvius (Italy); 13) Etna (Italy); 14) Santorini (Greece); 15) Niragongo (Zaire). [Source: International Association of Volcanology and Chemistry of the Earth's Interior]

Geology of Indonesia

Indonesia lies in the Ring of Fire and is one the most volcanically active and earthquake prone areas on earth. The islands in Indonesia were created mostly by volcanic activity and ocean mountain-building activity created by the movement of tectonic plates in Asia, the Indian Ocean and the Pacific Ocean. In the area of Indonesia, two large plates—the Indian Ocean and western Pacific plates—slide under an even more massive plate—the Eurasian plate—and the Eurasian and Australian continental plates collide.

Tectonically, this region--especially Java--is highly unstable, and although the volcanic ash has resulted in fertile soils, it makes agricultural conditions unpredictable in some areas. The country has numerous mountains and some 400 volcanoes, of which approximately 100 are active. Indonesia was forced up from geological plates from Australia, Asia and the Pacific. A deep trench runs along the southern coast of the Indonesian chain.

The collision of the Eurasian and Australian continental plates form a subduction zone that produces numerous earthquakes and a chain of volcanoes that runs from Sumatra through Java to New Guinea with a a few side branches to Sulawesi and the Molluccas. At subduction zones two plates collide head on, with one plate going over the top, forcing the other one down. In some cases the motion produces a descending convection current that sucks down the ocean floor. In these places deep seas trenches form; mountain building activity and earthquakes occur; and millions of tons of rock sink into the crust everyday. Subduction faults are usually angled at about 10 to 15 percent and often located where major oceans and continents meet. Where ocean crust, pushed down by the weigh of ocean water, is shoved under the thick crust of continents, the rock is heated, causing water and gases to bubble out. As they rise they melt the rock above it, creating magma that can fuel volcanoes.

Geographers believe that the island of New Guinea, of which Papua is a part, may once have been part of the Australian continent. The breakup and tectonic action created both towering, snowcapped mountain peaks lining its central east-west spine and hot, humid alluvial plains along the coast of New Guinea. Papua's mountains range some 650 kilometers east to west, dividing the province between north and south. [Source: Library of Congress]

Volcanos and Tectonics of Indonesia

The Indonesian region is one of the most seismically active zones of the earth; at the same time it has a leading position from the point of view of active and potentially active volcanoes. It is a typical island-arc structure with its characteristic physiographic features, such as a deep oceanic trench, a geanticline belt, a volcanic inner arc and a marginal basin. In most subduction zones, motion of the subducted plate is nearly perpendicular to the trench axis. In some cases, for example Sumatra, where the motion is oblique to the axis, a strike-slip fault zone is seen, and is lying parallel to the volcanic chain. [Source: USGS]

Most of Indonesia's volcanoes are part of the Sunda arc, a 3,000-km-long line of volcanoes extending from northern Sumatra to the Banda Sea. Most of these volcanoes are the result of subduction of the Australia Plate beneath the Eurasia Plate. Volcanoes in the Banda Sea result from subduction of the Pacific Plate under the Eurasia Plate. About one-fourth of Indonesia's volcanoes are north of the Sunda arc in an area with complex tectonics. Several small plates have produced mostly north-south trending subduction zones. The volcanoes of Sulawesi, Halmahera, and Sangihe are the result of these subduction zones. [Source: USGS]

The distribution of earthquakes in the subducted plates can be used to make a cross-section of the Molucca Sea area. Most of the Molucca Sea Plate has been "consumed" (subducted) by the Halmahera subduction zone in the east and by the Sangihe subduction zone in the west. The volcanoes of Sulawesi, Sangihe, and Halmahera are fed by magma generated in the asthenospheric mantle that has been modified by fluids derived from the subducted Molucca Sea Plate. In a few million years, all of the Molucca Sea Plate will be subducted and the Sangihe and Halmahera plates will collide, shutting off volcanism. Simplified from Hamilton (1979).

In the subduction zone southwest of Sumatra, the Sunda trench axis strikes approximately north 37̊W. The Indian Ocean crust is moving in an azimuth of approximately north 23̊E relative to Southeast Asia, giving an angle of obliquity of 60̊. Eastern Indonesia, forming the southeastern extremity of the Southeast Asian lithospheric plate, crushed between the northward-moving Indo-Australian and the westward-moving Pacific plates, is certainly the most complex active tectonic zone on earth. The rate of subduction is some centimeters per year; for example, it is 6.0 cm per year in the West Java Trench at 0̊S 97̊E (azimuth 23̊); 4.9 cm per year in the East Java Trench at 12̊S 120̊E (azimuth 19̊); and 10.7 cm per year in New Guinea at 3̊S 142̊E (azimuth 75̊).

Frequent volcanic eruptions and frequent earthquake shocks testify to the active tectonic processes which are currently in progress in response to the continued movement of these major plates. The distribution of small ocean basins, continental fragments, remnants of ancient magmatic arcs and numerous subduction complexes which make up the Indonesian region indicate that the past history of the region was equally tectonically active.

Dangerous Volcanoes in Indonesia

Indonesia has 76 volcanoes that have erupted in historic time - the largest number for any volcanic region. These volcanoes have had at least 1,171 eruptions, placing Indonesia second (after Japan) for the region with the most dated eruptions. Indonesia has had the highest number of eruptions that: 1) produced fatalities; 2) caused damage to land used for agriculture; 3) generated mudflows; 4) generated tsunamis; 5) grew lava domes; 6) produced pyroclastic flows Some of Indonesia's more notorious volcanoes include: 1) Agung, Bali; 2) Colo, Suluwesi; 3) Dieng, Java; 4) Galunggung, Java; 5) Gamalama, Halmahera; 6) Kelut, Java; 7) Krakatau, Sunda Strait; 8) Merapi, Java; 9) Papandayan, Java; 10 ) Semeru, Java; and 11) Tambora, Sumbawa. [Source: USGS]

Indonesian volcanologist Surono told the Wall Street Journal: “There are 127 active volcanoes in Indonesia, so the difference that we are seeing now depends on each mountain. Eruption at Mount Merapi is rare, but massive once it erupts [like in 2010]. While for Mount Lokon, it erupts continuously on a smaller scale, so the duration for a warning status is also longer. Many mountains have been on watch alert for a long time, such as Sinabung and Merapi.” As of April 2014, four volcanoes in Indonesia were on a high-level III alert, including Mount Sinabung on Sumatra Island, which erupted for months in 2013, killing 15 people and forcing more than 20,000 to evacuate their homes. At that time Sinabung was listed as alert level IV, the highest. No volcanoes are currently on the highest alert. [Source: Resty Woro Yuniar, Wall Street Journal, September 13, 2013 ==, Ben Otto, Wall Street Journal, February 3, 2014]

Which of Indonesia’s volcanoes worry you the most and why? Surano said: “Mount Ijen in East Java. It has a lake that contains 36 million cubic meters of acid water with pH 0-0,2. It’s 20 times more acidic than a car battery! Even if it only erupts 10 percent [of its potential], it would trigger an acid tsunami. Imagine being near there...Indonesia has many volcanic islands, but I’d say Mount Colo in Una-Una Island [Central Sulawesi], Mt. Kie Besi in Makian Island [North Malacca], and Ternate Island. East Nusa Tenggara is also vulnerable. When Colo erupted in 1983, 90 percent of the island was clouded by hot volcanic ash. What worries me is now the residents want to go back to the island. ==

On the impact of the 2004 tsunami on Indonesia’s volcanoes, Surono said: “I believe it affected some of the mountains, not all. I know for sure that activity in some of volcanoes overseas increased due to the earthquake. When Nias [an island off the western coast of Sumatra, Indonesia] was shaken by the earthquake in 2004, Mount Talang erupted because the pressure was so high inside it that even a little disturbance could trigger the eruption. But not one volcano in Aceh Province erupted in the big earthquake of 2004. Tectonic earthquakes could affect a volcano if the pressure inside the mountain has matured enough. Just like a Coke. If you shake it hard enough, it will burst into the air. ==

On why eruptions can be dangerous in Indonesia, Surono sa: “Lack of infrastructure, lack of education for local residents, and lack of willingness from local government to be involved in mitigation plans. I want people to know that you can live near a volcano mountain as long as you know the risk and you know what to do [if it erupts]. ==

Some of the greatest volcano tragedies in Indonesia have been caused by lahars. "Lahar" is an Indonesian word that describes volcanic mudflows or debris flows. Lahars have the consistency, viscosity and approximate density of concrete: fluid when moving, solid at rest. Lahars can vary in size and speed. Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second. Large lahars hundreds of meters wide and tens of meters deep can flow several tens of meters per second: much too fast for people to outrun.

Avoiding Danger from Indonesia’s Volcanoes

The Volcanological Survey of Indonesia was established in 1920. In recent decades, the survey has evacuated people living near volcanoes prior to several large eruptions, avoiding fatalities except for a few eruptions. A few examples illustrate the value of carefully monitoring volcanoes: 1) n 1991, during the eruption of Lokon-Empung, 10,000 people were evacuated and there was only one fatality; 2) in 1990, during the eruption of Kelud, 60,000 people were evacuated and there were 32 fatalities; 3) in 1988, during the eruption of Makian, 15,000 people were evacuated and there were no fatalities; and 4) in 1982, during the eruption of Galunggung, 75,000 people were evacuated and there were 68 fatalities

About 165 local people died when Mt. Merapi erupted in 2010 primarily because many people refused to evacuate. Explaining why people wouldn’t leave their homes, Indonesian volcanologist Surono told the Wall Street Journal: “I believe that they thought it’s better to live in rickety huts under certainty than to live in shelters under uncertainty. This does not apply only to Merapi. Many people opt to live near volcanoes because the ground is very fertile and the view is enchanting. There’s a saying that if you leave a stick in a volcano, when you come back a month later, that stick will be a plant.” [Source: Resty Woro Yuniar, Wall Street Journal, September 13, 2013 ==]

Would fewer lives would be lost in a similar eruption there today? Surano said: “Yes, people there no longer believe in superstition. They believe in science now. When I recently visited the area, the women in the nearby villages already had a plastic bag with jewelry, money, and [their] marriage book inside…just in case. That makes me glad. Mitigation plans for any disaster must be prepared before it happens.” ==

Are rescue teams specially trained to deal with volcanic eruptions? Surano said: “Of course! There are many courses on how to be a good volunteer in Merapi. They have to know the do’s and don’t's around a volcano, though I must say, I want the local residents to learn how to save themselves. In a disaster, I want them to be the subject instead of object.” ==

On predicting eruptions, Surono said: “To define status, I use my intuition. It’s tough to determine whether a volcano would erupt or not. We can’t only depend on science or history. We are lacking on equipment that is precise. It depends on the watcher himself. Our equipment is also old. There is equipment that dates back to 1982. I want, by 2014, for all volcanoes watching equipment in Indonesia to be replaced with the new ones. So far, I’ve managed to replace the ones in volcanoes I considered priority, like the ones located near city, most active, and with eruption history. We can’t predict it because volcanoes’ characteristics differ from each other. You can’t even feel volcanic earthquake. You can only measure it by a tool.” ==

Volcanoes and Indonesians

Andrew Marshall of Associated Press wrote: “Nowhere else do so many live so close to so many active volcanoes. On Java alone, 120 million people live in the shadow of more than 30 volcanoes, a proximity that has proved fatal to more than 140,000 in the past 500 years. Death by volcano takes many forms: searing lava, suffocating mud, or the tsunamis that often follow an eruption. [Source: Andrew Marshall, Associated Press, January 2008 <>]

“Sumatra, the vast island northwest of Java, is home to the Batak people, converted to Christianity by European missionaries in the 19th century. Yet many still believe the first human descended from heaven on a bamboo pole to Mount Pusuk Buhit, an active volcano on the shores of Lake Toba. The Tengger, Hindus who live around Mount Bromo in East Java, periodically climb through choking sulfurous clouds to throw money, vegetables, chickens, and an occasional goat into the crater. On Flores, the Nage, Catholics like most on that island, are buried with their heads toward Mount Ebulobo, whose cone fills their southern horizon. <>

“On largely Hindu Bali, volcanoes are sacred, none more so than 10,000-foot (3,000 meters) Mount Agung, its highest peak. It is said a true Balinese knows its location, even when blindfolded, and many sleep with their heads pointing toward it. In 1963 a catastrophic eruption of Mount Agung killed a thousand people. Others starved to death after ash smothered their crops. "The very ground beneath us trembled with the perpetual shocks of the explosions," wrote an eyewitness. Yet what once was spoken of as divine wrath is now seen as a gift. The rock and sand thrown up by the eruption built hotels, restaurants, and villas for hordes of foreign tourists.

Bali Volcano

Mount Agung (northeast Bal) is a 3,142-meter-high active volcano that dominates Bali and is the highest mountain on the island. Known to Balinese as the "naval of the world," it erupted violently in 1963, killing about 500 people. Offerings of rice, a hard boiled eggs and some flowers blossoms are periodically left on the volcano to keep it quiet. The oval crater is about 500 meters across. The 3,142-meter-high figure dates back to before the eruption, when the volcano had its top blown off. It is now thought to be 3,014 meters high.

There are hiking routes to the summit, with the shortest ones taking only about three hours. The two most popular climbing routes are from the temple Pura Besakih and from Pura Pasat Agung. The are treks that begin at 2:00am and reach the summit for sunrise. Before you make the climb you should make an offering and on the way up the mountain should be treated with respect. That means no swearing or eating any food with beef in it. It advisable to take a guide and make the hike during the dry season. See the Lonely Planet books for details.

Bali Volcano Eruption

On March 16th, 1963 Bali’s Gunung Agung erupted for the first time in 120 years, with a follow up eruption in May, destroying much of northeastern Bali and killing 1,100 people and leaving 100,000 other homeless. Entire villages were destroyed by layers of ash and flows of hot mud that made it all the way to the sea. Hard rains after the eruption exacerbated the problems, creating landslides and lahars. Roads were closed off, villages were swept away and more people suffered, this time from lack of food. [Source: Windsor Booth, National Geographic, September 1963]

The Balinese call Mount Agung the "navel of the world." They regard it as the center of their universe. During the eruption a gate built to honor president Sukarno was destroyed. This was seen as a symbol of corruption in the government, which was soon ousted. Many Balinese believed that Sukarno caused the eruption by forcing religious leaders in Bali to “stage” an important ritual at a tourism conference.

Some 200 people died when a pyroclastic flow (an incandescent cloud of volcanic debris) raced down the mountain through the in the town of Subagan. Nearly all the inhabitants of the village of Lebih were burnt to death or suffocated by clouds of hot gas. Boiling mud and ash obliterated other towns, where children made strange wailing sounds as they choked to death. Some areas strewn with dog eaten bodies were still too hot to enter weeks after the eruption. Days became night as far away as Java when clouds of cinder and ash blew over and drinking water was in short in supply as rivers and streams became a silty grey mess.

Besakih, Bali's most sacred shrine is located right beneath the volcano. Even though there were dangers of new eruptions and the Governor of Bali forbade people from visiting the temple, thousands went anyway to celebrate an April full moon ceremony. Offerings to the gods included plaited palm fonds, bowls of rice, fried cakes, barbecued fowl, squat bananas and spiny durians. Some ceremonies are climaxed with women picking up burning coals in their bare hands.

Volcanoes and a Near Plane Crash

In 1982 British Airways pilot was flying over Indonesia with 263 passengers and crew when the Boeing 747 he was fling experienced a sudden loss. "We were at 37,000 feet when dust came billowing into the cabin and I smelled sulfur. Engine four began to run down, and I shut it off. Then we lost the others, one by one. For the next 13 minutes we were in the proud possession of the world's largest glider."♥

The plane had flown into an cloud from Galunggung on Java; the occasional eruptions were well known to local pilots but no to the others. Moody and the crew prepared to ditch at sea, all the while trying to restart the engines. Finally they emerged from the ash cloud. "Around 13,000 number four restarted, then the others," he said. In the cooled engines, the glass coating apparently shattered and thrust returned. The plane landed at Jakarta with instruments impaired and the front windows opaque with ash.♥

Image Sources:

Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Lonely Planet Guides, Library of Congress, Compton’s Encyclopedia, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Global Viewpoint (Christian Science Monitor), Foreign Policy, Wikipedia, BBC, CNN, and various books, websites and other publications.

Page Top

© 2008 Jeffrey Hays

Last updated June 2015

This site contains copyrighted material the use of which has not always been authorized by the copyright owner. Such material is made available in an effort to advance understanding of country or topic discussed in the article. This constitutes 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. If you are the copyright owner and would like this content removed from factsanddetails.com, please contact me.