Mount Tambora (or Tamboro) is an active stratovolcano which is a peninsula of and the highest peak on the island of Sumbawa in 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 one of the tallest peaks in the Indonesian archipelago in the 18th century. 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 had a volcanic explosivity index (VEI) of 7, the only unambiguously confirmed VEI-7 eruption since the Lake Taupo eruption in about AD 180. (The 946 eruption of Paektu Mountain might also have 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, more than 2,000 km (1,200 mi) away. Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, Java, and the Maluku Islands. Most of the 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 11,000–12,000 were killed directly by the eruption; the oft-cited figure of 92,000 people killed is believed to be an overestimate.
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-metre-deep pyroclastic deposits. At the site, dubbed the “Pompeii of the East”, the artifacts were preserved in the positions they had occupied in 1815.
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 takes only 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 western 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.
Tambora is 340 km (210 mi) north of the Java Trench system and 180–190 km (110–120 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 4m 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.