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Volcanoes in Indonesia

The geography of Indonesia is dominated by volcanoes that are formed due to subduction zones between the Eurasian plate and the Indo-Australian plate. Some of the volcanoes are notable for their eruptions, for instance, Krakatau for its global effects in 1883, Lake Toba for its supervolcanic eruption estimated to have occurred 74,000 Before Present which was responsible for six years of volcanic winter, and Mount Tambora for the most violent eruption in recorded history in 1815.

Mount Tambora
Mount Tambora on Sumbawa

Mount Tambora (or Tomboro) is an active stratovolcano on Sumbawa island, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zones beneath it. This raised Mount Tambora as high as 4,300 m (14,000 ft), making it one of the tallest peaks in the Indonesian archipelago, and drained off a large magma chamber inside the mountain. It took centuries to refill the magma chamber, its volcanic activity reaching its peak in April 1815.

Tambora erupted in 1815 with a rating of seven on the Volcanic Explosivity Index; the largest eruption since the Lake Taupo eruption in AD 181. The explosion was heard on Sumatra island (more than 2,000 km or 1,200 mi away). Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, Java and Maluku islands.

The death toll was at least 71,000 people, of which 11,000 - 12,000 were killed directly by the eruption; most authors estimated 92,000 people were killed but this figure is based on an overestimated calculation. The eruption created global climate anomalies; 1816 became known as the Year Without a Summer because of the effect on North American and European weather. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in the worst famine of the 19th century.

During an excavation in 2004, a team of archaeologists discovered cultural remains buried by the 1815 eruption. They were kept intact beneath the 3 m (10 ft) deep pyroclastic deposits. Dubbed the Pompeii of the East, the artifacts were preserved in the positions they had occupied in 1815.

Geographical setting

Mount Tambora is located on Sumbawa island, part of the Lesser Sunda Islands. It is a segment of the Sunda Arc, a string of volcanic islands that form the southern chain of the Indonesian archipelago. Tambora forms its own peninsula on Sumbawa, known as the Sanggar peninsula. At the north of the peninsula is the Flores Sea, and at the south is the 86 km (53.5 mi) long and 36 km (22 mi) wide Saleh Bay. At the mouth of Saleh Bay there is an islet called Mojo.
Besides the seismologists and vulcanologists who monitor the mountain's activity, Mount Tambora is an area of scientific studies for archaeologists and biologists. The mountain also attracts tourists for hiking and wildlife activities. The two nearest cities are Dompu and Bima. There are three concentrations of villages around the mountain slope. At the east is Sanggar village, to the northwest are Doro Peti and Pesanggrahan villages, and to the west is Calabai village.

There are two ascent routes to reach the caldera. The first route starts from Doro Mboha village at the southeast of the mountain. This route follows a paved road through a cashew plantation until it reaches 1,150 m (3,800 ft) above sea level. The end of this route is the southern part of the caldera at 1,950 m (6,400 ft), reachable by means of a hiking track. This location is usually used as a base camp to monitor the volcanic activity, because it only takes one hour to reach the caldera. The second route starts from Pancasila village at the northwest of the mountain. Using the second route, the caldera is only accessible by foot.

In August 2011, the alert level for the volcano was raised from Level I to Level II after increasing activity was reported in the caldera, including earthquakes and smoke emissions.

Geological history


Tambora lies 340 km (211 mi) north of the Java Trench system and 180–190 km (112–118 mi) above the upper surface of the active north-dipping subduction zone. Sumbawa island is flanked to both the north and south by the oceanic crust. The convergence rate is 7.8 cm/year (3 in/year). The existence of Tambora is estimated to have begun around 57 ka BP. Its ascent has drained off a large magma chamber inside the mountain. The Mojo islet was formed as part of this geological process in which Saleh Bay first appeared as a sea basin (about 25 ka ago).

According to a geological survey, a high volcanic cone with a single central vent was formed before the 1815 eruption, which follows a stratovolcano shape. The diameter at the base is 60 km (37 mi). The central vent emitted lava frequently, which cascaded down a steep slope.

Since the 1815 eruption, the lowermost portion contains deposits of interlayered sequences of lava and pyroclastic materials. Approximately 40% of the layers are represented in the 1–4 m (3.3–13.1 ft) thick lava flows. Thick scoria beds were produced by the fragmentation of lava flows. Within the upper section, the lava is interbedded with scoria, tuffs and pyroclastic flows and falls. There are at least 20 parasitic cones. Some of them have names: Tahe (877 m), Molo (602 m), Kadiendinae, Kubah (1648 m) and Doro Api Toi. Most of these parasitic cones have produced basaltic lava flows.

Eruptive history

Using radiocarbon dating technique, it has been established that Mount Tambora had erupted three times before the 1815 eruption, but the magnitudes of these eruptions are unknown. Their estimated dates are 3910 BC ± 200 years, 3050 BC and AD 740 ± 150 years. They all shared similar eruptive characteristics: central vent eruption and explosive eruption, except the lattermost eruption had no pyroclastic flows.

In 1812, Mount Tambora became highly active, with its eruptive peak in April 1815. The magnitude was seven on the Volcanic Explosivity Index (VEI) scale, with a total tephra ejecta volume of 1.6 × 1011 cubic metres. Its eruptive characteristics included central vent and explosive eruptions, pyroclastic flows, fatalities, land and property damage, tsunamis and caldera collapse. It created a long-term effect on global climate.

This activity ceased on 15 July 1815. A follow-up activity was recorded in August 1819 consisting of a small eruption with flames and rumbling aftershocks, and was considered to be part of the 1815 eruption. This eruption was recorded at two on the VEI scale. Around 1880 ± 30 years, Tambora went into eruption again, but only inside the caldera. It created small lava flows and lava dome extrusions; this was recorded at two on the VEI scale. This eruption created the Doro Api Toi parasitic cone inside the caldera.

Mount Tambora is still active. Minor lava domes and flows have been extruded on the caldera floor during the 19th and 20th centuries. The last eruption was recorded in 1967. However, it was a very small eruption with scale zero on the VEI, which means it was a non-explosive type of eruption.

1815 eruption

Chronology of the eruption

Mount Tambora experienced several centuries of inactivity before 1815, known as dormancy, as the result of the gradual cooling of hydrous magma in a closed magma chamber. Inside the chamber at depths between 1.5–4.5 km (5,000–15,000 ft), the exsolution of a high pressure magma fluid formed during cooling and crystallisation of the magma. Overpressure of the chamber of about 4–5 kbar was generated and the temperature ranged from 700 °C–850 °C (1,300–1,500 °F).
In 1812, the caldera began to rumble and generated a dark cloud. On 5 April 1815, a moderate-sized eruption occurred, followed by thunderous detonation sounds, heard in Makassar on Sulawesi (380 km or 236 mi), Batavia (now Jakarta) on Java (1,260 km or 783 mi), and Ternate on the Molucca Islands (1400 km or 870 mi). What was first thought to be sound of firing guns was heard on 10–11 April on Sumatra island (more than 2,600 km or 1,615 mi away). On the morning of 6 April, volcanic ash began to fall in East Java with faint detonation sounds lasting until 10 April.

At about 7 p.m. on 10 April, the eruptions intensified. Three columns of flame rose up and merged. The whole mountain was turned into a flowing mass of "liquid fire". Pumice stones of up to 20 cm (8 inches) in diameter started to rain down at approximately 8 p.m., followed by ash at around 9–10 p.m. Hot pyroclastic flows cascaded down the mountain to the sea on all sides of the peninsula, wiping out the village of Tambora. Loud explosions were heard until the next evening, 11 April. The ash veil had spread as far as West Java and South Sulawesi. A "nitrous" odor was noticeable in Batavia and heavy tephra-tinged rain fell, finally receding between 11 and 17 April.

The explosion is estimated to have been at scale seven on the Volcanic Explosivity Index. It had roughly four times the energy of the 1883 Krakatoa eruption. An estimated 100 km³ (38.6 mi³) of pyroclastic trachyandesite was ejected, weighing approximately 1.4×1014 kg. This has left a caldera measuring 6–7 km (4–5 mi) across and 600–700 m (2,000–2,300 ft) deep. The density of fallen ash in Makassar was 636 kg/m². Before the explosion, Mount Tambora was approximately 4,300 m (14,000 ft) high, one of the tallest peaks in the Indonesian archipelago. After the explosion, it now measures only 2,851 m (9,300 ft).

The 1815 Tambora eruption is the largest observed eruption in recorded history (see Table I, for comparison). The explosion was heard 2,600 km (1,600 mi) away, and ash fell at least 1,300 km (800 mi) away. A pitch of darkness was observed as far away as 600 km (370 mi) from the mountain summit for up to two days. Pyroclastic flows spread at least 20 km (12.5 mi) from the summit.


All vegetation on the island was destroyed. Uprooted trees, mixed with pumice ash, washed into the sea and formed rafts of up to 5 km (3 mi) across. One pumice raft was found in the Indian Ocean, near Calcutta on 1 and 3 October 1815. Clouds of thick ash still covered the summit on 23 April. Explosions ceased on 15 July, although smoke emissions were still observed as late as 23 August. Flames and rumbling aftershocks were reported in August 1819, four years after the event.

A moderate-sized tsunami struck the shores of various islands in the Indonesian archipelago on 10 April, with a height of up to 4 m (13 ft) in Sanggar at around 10 p.m. A tsunami of 1–2 m (3–6 ft) in height was reported in Besuki, East Java, before midnight, and one of 2 m (6 ft) in height in the Molucca Islands.

The eruption column reached the stratosphere, an altitude of more than 43 km (140,000 ft). The coarser ash particles fell 1 to 2 weeks after the eruptions, but the finer ash particles stayed in the atmosphere from a few months up to a few years at an altitude of 10–30 km (33,000–100,000 ft). Longitudinal winds spread these fine particles around the globe, creating optical phenomena. Prolonged and brilliantly colored sunsets and twilights were frequently seen in London, England between 28 June and 2 July 1815 and 3 September and 7 October 1815. The glow of the twilight sky typically appeared orange or red near the horizon and purple or pink above.

The estimated number of deaths varies depending on the source. Zollinger (1855) puts the number of direct deaths at 10,000, probably caused by pyroclastic flows. On Sumbawa island, there were 38,000 deaths due to starvation, and another 10,000 deaths occurred due to disease and hunger on Lombok island. Petroeschevsky (1949) estimated about 48,000 and 44,000 people were killed on Sumbawa and Lombok, respectively. Several authors use Petroeschevsky's figures, such as Stothers (1984), who cites 88,000 deaths in total. However, Tanguy et al. (1998) claimed Petroeschevsky's figures to be unfounded and based on untraceable references. Tanguy revised the number solely based on two credible sources, i.e., Zollinger, who himself spent several months on Sumbawa after the eruption, and Raffles's notes. Tanguy pointed out that there may have been additional victims on Bali and East Java because of famine and disease. Their estimate was 11,000 deaths from direct volcanic effects and 49,000 by post-eruption famine and epidemic diseases. Oppenheimer (2003) stated a modified number of at least 71,000 deaths in total, as seen in the table below.

Comparison of selected volcanic eruptions
 Eruptions Year Column
height (km)
VEI N. hemisphere
summer anomaly (°C)
 Taupo 181 51 7 ? unlikely
 Baekdu 969 25 6–7 ? ?
 Kuwae 1452 ? 6 −0.5 ?
 Huaynaputina 1600 46 6 −0.8 ≈ 1400
 Tambora 1815 43 7 −0.5 > 71,000
 Krakatau 1883 25 6 −0.3 36,600
 Santamaría 190 34 6 no anomaly 7,000–13,000
 Katmai 1912 32 6 −0.4 2
 Mt. St. Helens 1980 19 5 no anomaly 57
 El Chichón 1982 32 4–5 ? > 2,000
 Nevado del Ruiz 1985 27 3 no anomaly 23,000
 Pinatubo 1991 34 6 −0.5 1202
 Source: Oppenheimer (2003) and Smithsonian Global Volcanism Program for VEI.

Global effects

The 1815 eruption released sulfur into the stratosphere, causing a global climate anomaly. Different methods have estimated the ejected sulfur mass during the eruption: the petrological method; an optical depth measurement based on anatomical observations; and the polar ice core sulfate concentration method, using cores from Greenland and Antarctica. The figures vary depending on the method, ranging from 10 Tg S to 120 Tg S.

In the spring and summer of 1816, a persistent dry fog was observed in the northeastern U.S. The fog reddened and dimmed the sunlight, such that sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the "fog". It was identified as a stratospheric sulfate aerosol veil. In summer 1816, countries in the Northern Hemisphere suffered extreme weather conditions, dubbed the Year Without a Summer.

Average global temperatures decreased about 0.4–0.7 °C (0.7–1.3 °F), enough to cause significant agricultural problems around the globe. On 4 June 1816, frosts were reported in Connecticut, and by the following day, most of New England was gripped by the cold front. On 6 June 1816, snow fell in Albany, New York, and Dennysville, Maine. Such conditions occurred for at least three months and ruined most agricultural crops in North America. Canada experienced extreme cold during that summer. Snow 30 cm (12 in) thick accumulated near Quebec City from 6 to 10 June 1816.

1816 was the second coldest year in the northern hemisphere since AD 1400, after 1601 following the 1600 Huaynaputina eruption in Peru. The 1810s are the coldest decade on record, a result of Tambora's 1815 eruption and other suspected eruptions somewhere between 1809 and 1810 (see sulfate concentration figure from ice core data). The surface temperature anomalies during the summer of 1816, 1817 and 1818 were −0.51, −0.44 and −0.29 °C, respectively. As well as a cooler summer, parts of Europe experienced a stormier winter.

This pattern of climate anomaly has been blamed for the severity of typhus epidemic in southeast Europe and the eastern Mediterranean between 1816 and 1819. Much livestock died in New England during the winter of 1816–1817. Cool temperatures and heavy rains resulted in failed harvests in the British Isles. Families in Wales traveled long distances as refugees, begging for food. Famine was prevalent in north and southwest Ireland, following the failure of wheat, oat and potato harvests. The crisis was severe in Germany, where food prices rose sharply. Due to the unknown cause of the problems, demonstrations in front of grain markets and bakeries, followed by riots, arson and looting, took place in many European cities. It was the worst famine of the 19th century.

Archaeological evidence

In summer 2004, a team from the University of Rhode Island, the University of North Carolina at Wilmington, and the Indonesian Directorate of Volcanology, led by Haraldur Sigurdsson, began an archaeological dig in Tambora. Over six weeks, the team unearthed the first evidence of a lost culture that had been obliterated by the Tambora eruption. The site is located about 25 km (15.5 mi) west of the caldera, deep in the jungle, 5 km (3 mi) from the shore. The team had to cut through a deposit of volcanic pumice and ash 3 m (10 ft) thick.

The team used a ground-penetrating radar to locate a small buried house. They excavated the house, where they found the remains of two adults, as well as bronze bowls, ceramic pots, iron tools and other artifacts. The design and decoration of the artifacts have similarities with artifacts from Vietnam and Cambodia. Tests conducted using a carbonization technique revealed they were composed of charcoal formed by the heat of the magma.

All the people, the house and their culture are preserved as they were in 1815. Sigurdsson dubbed it the Pompeii of the East. Based on the artifacts found, which were mainly bronze objects, the team concluded that the people were not poor. Historical evidence indicates that people on Sumbawa island were known in the East Indies for their honey, horses, sappan wood for producing red dye, and sandalwood used for incense and medications. The area was thought to be highly productive agriculturally.

The archaeological findings suggest that there was a culture on Sumbawa that was wiped out by the 1815 eruption. The title Lost Kingdom of Tambora was coined by media. With this discovery, Sigurdsson intends to return to Tambora in 2007 to search for the rest of the villages, and hopefully to find a palace.


A scientific team led by a Swiss botanist, Heinrich Zollinger, arrived on Sumbawa in 1847. Zollinger's mission was to study the eruption scene and its effects on the local ecosystem. He was the first person to climb to the summit after the eruption. It was still covered by smoke. As Zollinger climbed up, his feet sank several times through a thin surface crust into a warm layer of powder-like sulfur. Some vegetation had re-established itself and a few trees were observed on the lower slope. A Casuarina forest was noted at 2,200–2,550 m (7,200–8,400 ft). Several Imperata cylindrica grasslands were also found.

Habitation of the mountain began in 1907. A coffee plantation was started in the 1930s on the northwestern slope of the mountain, in the Pekat village. A dense rain forest, called Duabangga moluccana, had grown at an altitude of 1,000–2,800 m (3,300–9,000 ft). It covers an area up to 80,000 hectares (800 km²). The rain forest was discovered by a Dutch team, led by Koster and de Voogd in 1933. From their accounts, they started their journey in a "fairly barren, dry and hot country", and then they entered "a mighty jungle" with "huge, majestic forest giants". At 1,100 m (3,600 ft), they entered a montane forest. Above 1,800 m (6,000 ft), they found Dodonaea viscosa dominated by Casuarina trees. On the summit, they found sparse Anaphalis viscida and Wahlenbergia.

56 species of birds were found in 1896, including the Crested White-eye. Twelve further species were found in 1981. Several other zoological surveys followed, and found other bird species on the mountain, resulting in over 90 bird species discoveries. Yellow-crested Cockatoos, Zoothera thrushes, Hill Mynas, Green Junglefowl and Rainbow Lorikeets are hunted for the cagebird trade by the local people. Orange-footed Scrubfowl are hunted for food. This bird exploitation has resulted in a decline in the bird population. The Yellow-crested Cockatoo is nearing extinction on Sumbawa island.

Since 1972, a commercial logging company has been operating in the area, which poses a threat to the rain forest. The logging company holds a timber-cutting concession for an area of 20,000 hectares (200 km²), or 25% of the total area. Another part of the rain forest is used as a hunting ground. In between the hunting ground and the logging area, there is a designated wildlife reserve where deer, water buffalos, wild pigs, bats, flying foxes, and various species of reptiles and birds can be found.


Indonesia's population has been increasing rapidly since the 1815 eruption. As of 2006, the population of Indonesia has reached 222 million people, of which 130 million are concentrated on Java and Bali islands. A volcanic eruption as large as the Tambora 1815 eruption would cause catastrophic devastation with more fatalities. Therefore, volcanic activity in Indonesia is continuously monitored, including that of Mount Tambora.

Seismic activity in Indonesia is monitored by the Directorate of Vulcanology and Geological Hazard Mitigation, Indonesia. The monitoring post for Mount Tambora is located at Doro Peti village. They focus on seismic and tectonic activities by using a seismograph. Since the 1880 eruption, there has been no significant increase in seismic activity. However, monitoring is continuously performed inside the caldera, especially around the parasite cone Doro Api Toi.

The directorate has defined a hazard mitigation map for Mount Tambora. Two zones are declared: the dangerous zone and the cautious zone. The dangerous zone is an area that will be directly affected by an eruption: pyroclastic flow, lava flow and other pyroclastic falls. This area, including the caldera and its surroundings, covers up to 58.7 km² (14,500 acres). Habitation of the dangerous zone is prohibited.

The cautious zone includes areas that might be indirectly affected by an eruption: lahar flows and other pumice stones. The size of the cautious area is 185 km² (45,700 acres), and includes Pasanggrahan, Doro Peti, Rao, Labuan Kenanga, Gubu Ponda, Kawindana Toi and Hoddo villages. A river, called Guwu, at the southern and northwest part of the mountain is also included in the cautious zone.

Location map of Mount Tambora

All text in this article is available under the terms of the GNU Free Documentation License
Last revised on September 03, 2011
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