Mount Tambora: Indonesian stratovolcano and the great 1815 eruption

Tambora is located on Sumbawa, one of the Lesser Sunda Islands. It forms a segment of the Sunda Arc, a chain of volcanic islands that make up the southern part of the Indonesian archipelago. Tambora is located on a peninsula of Sumbawa called the Sanggar Peninsula. To the north of this peninsula is the Floressee, and to the south is Saleh Bay, 86 km long and 36 km wide. In the mouth of the bay is the small island of Mojo.

Archaeology

In addition to seismologists and volcanologists who monitor the mountain's activity, biologists and archaeologists also conduct scientific studies in the Tambora area. In 2004, a team of volcanologists led by Haraldur Sigurdsson discovered a village buried under pyroclastic deposits near the crater (caldera) by the 1815 eruption. Bones and artifacts were recovered at the excavation site. At this site - also referred to as the "Pompeii of the East" in the press at the time because of the similar demise of the village - archaeologists hoped to have found the palace of the Rajah of the Tambora "kingdom" destroyed by the eruption. So far, there have been no other finds under the thick layers of material ejected from the crater.

Tourism

Today, the area also serves as a tourist destination. The two nearest towns are Dompu and Bima. Around the mountain slope are three villages, Sanggar in the east, Doro Peti and Pesanggrahan in the northwest, and the small town of Calabai on the west coast.

The caldera is accessible via two different routes. The first starts in the village of Doro Mboha to the south-east of the mountain and leads along a paved road to an altitude of 1150 m above sea level through kashu plantations. The end of this route is the southern part of the caldera at 1950 m above sea level, which can be reached by a hiking trail. This place is usually used as a base camp for volcano watching, as the caldera can be reached from there in about an hour. The second route starts from the village of Pancasila on the northwest side of the mountain. A driveway continues for about 7 km through coffee plantations to Lerang Tambora, a settlement of coffee planters, from where a sometimes arduous trail continues initially through dense tropical rainforest.

Formation

Tambora lies 340 kilometres north of the Sunda Trench and 180 to 190 kilometres above the upper margin of the north-dipping Benioff Zone. Sumbawa is fringed by oceanic crust to the north and south. The rate of convergence of the Indo-Australian, Eurasian and Pacific plates meeting here is about 7.8 centimetres per year. The age of Tambora is estimated to be at least 57,000 years.

Tambora measures about 60 kilometers at sea level. The current altitude is 2850 m compared to an estimated 4300 m before the eruption in 1815.

According to a geological survey, before the eruption Tambora had a high volcanic cone with a central shaft from which lava frequently escaped and flowed down the flanks of the mountain. Today, the stratovolcano consists of the volcanic deposits within the caldera, which reach up to its rim with heights of up to 2700 m in the northwest and up to 2750 m in the west and southwest.

The older stratovolcano consists of interlocking layers of lava and pyroclastics, the successor is formed to about 40% of one to four meters thick, often interrupted lava flows.

There are at least 20 subsidiary cones, some of which have been named: "Tahe" (877 meters), "Molo" (602 meters), "Kadiendinae", "Kuba" (1648 m) and "Doro Api Toi". Most of these secondary cones produced basalt lava flows.

Eruption history

Radiocarbon dating has shown that there were three eruptions of Tambora before 1815, but their magnitude is unknown. The dates are estimated to be 3710 BC (± 200 years), 3050 BC and 740 AD (± 150 years). All eruptions had comparable characteristics: an explosive eruption of the volcano from the central eruption channel, with the last one having no pyroclastic flows.

In 1812, Tambora became highly active, reaching its eruptive maximum in April 1815. The eruption was equivalent to a magnitude seven on the VEI scale, with a total of 60 to 160 cubic kilometers of ejected pyroclastic precipitation. Features of the eruption included explosive eruptions from the central channel, pyroclastic flows, tsunamis, and a caldera collapse. The eruption had long-term effects on global climate. Follow-up activity from the volcano was recorded in August 1819 in the form of a small eruption of magnitude two on the VEI scale. Between 1850 and 1910, eruptions occurred again, but were confined to the caldera. Small lava flows and domes were created. The strength was two on the VEI scale. During these eruptions, the "Doro Api Toi" - a secondary cone within the caldera - was created.

The last eruption of Tambora was recorded in 1967, and it was a very small, non-explosive eruption.