Mount Tambora

Mount Tambora (or Tamboro) is an active stratovolcano which is a peninsula of the island of Sumbawa, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zone beneath it. This raised Mount Tambora as high as 4,300 m (14,100 ft), making it, in the 18th century, one of the tallest peaks in the Indonesian archipelago. After a large magma chamber inside the mountain filled over the course of several decades, volcanic activity reached a historic climax in the eruption of 10 April 1815. This eruption was about a volcanic explosivity index (VEI) of 7, the only eruption unambiguously confirmed of that size since the Lake Taupo eruption in about 180 CE. (The Heaven Lake eruption of Baekdu Mountain around 969 CE may have also been VEI-7.)

With an estimated ejecta volume of 160 km³ (38 cu mi), Tambora's 1815 outburst is the largest volcanic eruption in recorded history. The explosion was heard on Sumatra island more than 2,000 km (1,200 mi) away. Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, Java, and Maluku Islands. Most deaths from the eruption were from starvation and disease, as the eruptive fallout ruined agricultural productivity in the local region. The death toll was at least 71,000 people, of whom 11,000â€"12,000 were killed directly by the eruption; the often-cited figure of 92,000 people killed is believed to be overestimated.

The eruption caused global climate anomalies that included the phenomenon known as "volcanic winter": 1816 became known as the "Year Without a Summer" because of the effect on North American and European weather. 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-deep pyroclastic deposits. At the site, dubbed the 'Pompeii of the East', the artifacts were preserved in the positions they had occupied in 1815.

§Geographical setting

Mount Tambora is on Sumbawa Island, part of the Lesser Sunda Islands. It is a segment of the Sunda Arc, a string of volcanic islands that forms the southern chain of the Indonesian archipelago. Tambora forms the Sanggar peninsula on Sumbawa. At the north of the peninsula is the Flores Sea, and at the south is Saleh Bay, 86 km (53 mi) long and 36 km (22 mi) wide. At the mouth of Saleh Bay is a 30,000-hectare islet called Moyo (Indonesian: Pulau Moyo) which has a guest shelter or luxurious resort where celebrities such as Princess Diana once stayed.

Besides its interest for seismologists and volcanologists, who monitor the mountain's activity, Mount Tambora is an area of scientific studies for archaeologists and biologists. It also attracts tourists for hiking and wildlife activities. The two nearest cities are Dompu and Bima. Three concentrations of villages are 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.

Three ascent routes are used to reach the caldera. The first route starts from Doro Mboha village south of the mountain, and follows a paved road through a cashew plantation until it reaches 1,150 m (3,770 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 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 is southwest of the mountain, starting from Doro Peti village; the Tambora volcanic monitoring station is in Doro Peti. The third route starts from Pancasila village northwest of the mountain, and passes through a coffee plantation. Using the third route, the caldera is accessible only by foot. The highest point of Tambora is on a hill near the westen rim of the caldera.

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. In September 2011, the alert level was raised to level III after further increases in activity.

§Geological history

§Formation

Tambora is 340 km (210 mi) north of the Java Trench system and 180â€"190 km (110â€"120 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 (3.1 in) per year. Tambora is estimated to have formed around 57,000 years ago. Depositing its strata 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, collapsing into the caldera of the drained magma chamber, first appeared as a sea basin, about 25,000 years ago.

According to a geological survey before the 1815 eruption, Tambora had the shape of a typical stratovolcano, with a high symmetrical volcanic cone soaring up to 4,300 m (14,100 ft) above the sea level, and a single central vent. 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. The 1- to 4-m-thick lava flows constitute about 40% of the layers' thickness. 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. At least 20 subsidiary or parasitic cones are known. Some of them have names: Tahe, 844 m (2,769 ft); Molo, 602 m (1,975 ft); Kadiendinae; Kubah, 1,648 m (5,407 ft); and Doro Api Toi. Most of these parasitic cones have produced basaltic lavas.

§Eruptive history

Radiocarbon dating has established the dates of three of Mount Tambora's eruptions before the 1815 eruption. The magnitudes of these eruptions are unknown. The estimated dates are 3910 BC ± 200 years, 3050 BC and 740 AD ± 150 years. They were all explosive central vent eruptions with similar characteristics, but the 740 AD eruption had no pyroclastic flows.

In 1812, Mount Tambora entered a period of high activity, with its climactic eruption being the catastrophic explosive event of April 1815. The VEI-7 eruption had a total tephra ejecta volume of 160 km³ (38 cu mi). It was an explosive central vent eruption with pyroclastic flows and a caldera collapse, causing tsunamis and extensive land and property damage. It had a long-term effect on global climate. This activity ceased on 15 July 1815. Follow-up activity was recorded in August 1819 consisting of a small eruption (VEI = 2) with flames and rumbling aftershocks, and was considered to be part of the 1815 eruption sequence. Around 1880 ± 30 years, Tambora went into eruption again, but only inside the caldera. Small lava flows and lava dome extrusions were formed. This eruption (VEI = 2) 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, non-explosive eruption (VEI = 0).

There have been reports of a similarly small eruption in 2011.

§1815 eruption

§Archaeological work

See Tambora culture for details about 2004 work on exploring for villages and people lost at the time of the major eruption.

§Ecosystem

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 sulphur. Some vegetation had re-established itself and a few trees were observed on the lower slope. A Casuarina forest was noted at 2,200â€"2,550 m (7,220â€"8,370 ft). Several Imperata cylindrica grasslands were also found.

Rehabitation of the mountain began in 1907. A coffee plantation was started in the 1930s on the northwestern slope of the mountain, in the village of Pekat. A dense rain forest, dominated by the pioneering tree, Duabanga moluccana, had grown at an altitude of 1,000â€"2,800 m (3,300â€"9,200 ft). It covers an area up to 80,000 ha (200,000 acres). The rain forest was explored 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 (5,900 ft), they found Dodonaea viscosa dominated by Casuarina trees. On the summit, they found sparse Anaphalis viscida and Wahlenbergia.

In 1896, 56 species of birds were found, 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 discovered on Mount Tambora. 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 large threat to the rain forest. The logging company holds a timber-cutting concession for an area of 20,000 ha (49,000 acres), 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.

§Exploration of the caldera floor

In the Tambora caldera formed by the massive eruption in 1815 an ecosystem has developed largely uninfluenced by human beings because of its isolation. Zollinger (1847) and later P. van Rheden (1913) and W.A. Petroeschevsky (1947) could only observe the caldera floor from the crater rim.

In October 2013, a German research team (Georesearch Volcanedo Germany) for the first time carried out a longer expedition into this caldera, about 1300 m deep, and with the help of a native team climbed down the southern caldera wall from 2430 m to 1340 m altitude, reaching the caldera floor while experiencing extreme conditions. A German geoscientist in the team was the first European woman and worldwide the first woman to conquer the almost impassable inner southern wall of this volcano. The team stayed within the Tambora caldera for nine days, researching the caldera floor. People had reached the caldera floor only in a few cases as the descent down the steep walls is difficult and dangerous, subject to earthquakes, landslides and rockfalls. Moreover, only relatively short stays on the caldera floor had been possible due to logistical problems, so that extensive studies had been impossible. The investigation program of Georesearch Volcanedo on the caldera floor included researching the visible effects of the smaller eruptions which had taken place on the caldera floor since 1815, temperature measurements (air, soil, gases), gas measurements, studies of flora and fauna and measurement of weather data. Especially striking were the relatively high activity of Doro Api Toi in the southern part of the caldera and the gases escaping under high pressure and loud noises on the lower north-east wall.

In July 2014 the same research team from Georesearch Volcanedo Germany carried out a further expedition into the Tambora caldera and set a new record, beating their own: Over 12 days the investigations of the previous year were continued and expanded. The results of these two expeditions will be published in due course.

§Monitoring

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. A contemporary volcanic eruption as large as Tambora's 1815 eruption would cause catastrophic devastation with likely many 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 parasitic 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 (22.7 sq mi). 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 (71 sq mi), and includes Pasanggrahan, Doro Peti, Rao, Labuan Kenanga, Gubu Ponda, Kawindana Toi and Hoddo villages. The river Guwu at the southern and northwest part of the mountain is also included in the cautious zone.

§See also

• List of volcanoes in Indonesia
• List of volcanic eruptions by death toll
• List of natural disasters
• Timetable of major worldwide volcanic eruptions

§References

§Further reading

§External links

• "Indonesia Volcanoes and Volcanics". Cascades Volcano Observatory. USGS. Retrieved 19 March 2006. 
• "Tambora, Sumbawa, Indonesia". Volcano World. Department of Geosciences at Oregon State University. 
• "Informative website about Tambora volcano".