Mount Tambora, also called Tomboro, is an active stratovolcano in West Nusa Tenggara, Indonesia. It is located on the island of Sumbawa in the Lesser Sunda Islands. Volcanic activity occurs there because of subduction zones. The eruption in 1815 was the largest in recorded history, producing up to 150 cubic kilometers of volcanic material, which gave it a VEI-7 rating on the Volcanic Explosivity Index. This eruption led to the summer of 1816 being called the "Year Without a Summer" because the eruption caused global cooling.
Geographical setting
Mount Tambora is located in the northern part of Sumbawa Island, which is part of the Lesser Sunda Islands. It is a part of the Sunda Arc, a group of volcanic islands that form the southern part of the Indonesian archipelago. Tambora creates its own peninsula on Sumbawa called the Sanggar Peninsula. To the north of the peninsula is the Flores Sea, and to the south is Saleh Bay, which is 86 kilometers (53 miles) long and 36 kilometers (22 miles) wide. At the entrance of Saleh Bay is a small island named Mojo.
In addition to scientists who study earthquakes and volcanoes, Mount Tambora is of interest to archaeologists and biologists. The mountain also draws tourists for hiking and wildlife activities, though only a few visit. The two closest cities are Dompu and Bima. There are three groups of villages near the mountain. To the east is Sanggar village, to the northwest are Doro Peti and Pesanggrahan villages, and to the west is Calabai village.
There are two paths to reach the caldera. The first starts at Doro Mboha village on the southeast side of the mountain. A paved road leads through a cashew plantation to an elevation of 1,150 meters (3,770 feet). The road ends at the southern edge of the caldera, which reaches 1,950 meters (6,400 feet) and can only be reached by hiking. This spot is about one hour from the caldera and is often used as a base camp for monitoring volcanic activity. The second path begins at Pancasila village on the northwest side of the mountain and is only accessible by walking. The 16-kilometer (10-mile) hike from Pancasila, which starts at 740 meters (2,430 feet), takes about 14 hours with several stops along the way. The trail passes through thick jungle and is home to wildlife such as Elaeocarpus trees, Asian water monitors, reticulated pythons, hawks, orange-footed scrubfowl, pale-shouldered cicadabirds (Coracina dohertyi), brown and scaly-crowned honeyeaters, yellow-crested cockatoos, yellow-ringed white-eyes, helmeted friarbirds, wild boar, Javan rusa, and crab-eating macaques.
History
Tambora is located 340 kilometers (210 miles) north of the Java Trench system and 180 to 190 kilometers (110 to 120 miles) above the upper surface of the active north-dipping subduction zone. Sumbawa Island is surrounded on the north and south by oceanic crust. The Australian Plate moves beneath the Sunda Plate at a rate of 7.8 centimeters (3.1 inches) per year. Scientists estimate that volcanic activity at Mount Tambora began between 57,000 and 43,000 years ago. A 2012 study used argon dating of the first lava flows before the caldera formed to support the 43,000-year estimate. The formation of Tambora emptied a large magma chamber already present under the mountain. The Mojo islet was created during this process, and Saleh Bay became a sea basin around 25,000 years ago.
Before the 1815 eruption, Tambora had a tall volcanic cone with a single central vent, shaped like a stratovolcano. The base of the volcano was 60 kilometers (37 miles) wide. Lava frequently flowed down steep slopes. Rocks from Tambora include trachybasalt and trachyandesite, which contain high levels of potassium. These rocks have crystals such as apatite, biotite, clinopyroxene, leucite, magnetite, olivine, and plagioclase, though the exact composition varies. Orthopyroxene is not found in trachyandesites. Olivine is most common in rocks with less than 53% silicon dioxide, but it is absent in more silica-rich rocks, which contain biotite crystals. Mafic rocks also have titanium magnetite, and trachybasalts are rich in plagioclase. Lavas from Tambora have higher levels of rubidium, strontium, and phosphorus pentoxide compared to those from Mount Rinjani. Tambora lavas also have slightly more zircon than Rinjani lavas.
The magma from the 1815 eruption came from the Earth’s mantle and was altered by materials from subducted sediments, fluids from the subducted crust, and processes in magma chambers. Strontium ratios in Tambora rocks are similar to those in Rinjani rocks but lower than those in Sangeang Api. Potassium levels in Tambora volcanic rocks are over 3% by weight, placing them in the shoshonite range of the alkaline series.
After the 1815 eruption, layers of lava and pyroclastic material were deposited. About 40% of these layers are lava flows between 1 and 4 meters (3.3 to 13.1 feet) thick. Thick scoria beds formed when lava flows broke apart. In the upper layers, lava is mixed with scoria, tuffs, pyroclastic flows, and pyroclastic falls. Tambora has at least 20 parasitic cones and lava domes, such as Doro Afi Toi, Kadiendi Nae, Molo, and Tahe. These vents produced basaltic lava flows.
Radiocarbon dating shows that Tambora erupted three times during the Holocene before 1815, though the size of these eruptions is unknown. Their estimated dates are 3910 BC ± 200 years, 3050 BC, and 740 AD ± 150 years. A caldera formed around 43,000 BC and was later filled with lava flows. Two pyroclastic eruptions created the Black Sands and Brown Tuff formations, with the last occurring between 3895 BC and 800 AD.
In 1812, Mount Tambora became very active, with its strongest eruptions in April 1815. The eruption had a Volcanic Explosivity Index (VEI) of 7, with up to 180 cubic kilometers of tephra ejected. The eruption included central vent explosions, pyroclastic flows, tsunamis, and caldera collapse. It affected global climate, leading to 1816 being called the "year without a summer" due to crop failures and famine. Volcanic activity stopped on 15 July 1815, but small eruptions with "flames" and rumbling occurred in August 1819, considered part of the 1815 event.
Between about 1880 and 1910, eruptions at Tambora were limited to the caldera, producing small lava flows and domes. This activity was recorded at VEI 2. A parasitic cone called Doro Api Toi formed inside the caldera.
Tambora remained active, with minor lava domes and flows forming in the 19th and 20th centuries. The last recorded eruption was in 1967, a non-explosive event with a VEI of 0. A very small eruption was reported in 2011, prompting an alert level increase due to earthquakes and steam emissions.
Tambora experienced violent eruptions starting on 5 April 1815, with the largest eruption in recorded history. The magma chamber had been emptied by earlier eruptions and refilled over centuries. The eruption was heard on Sumatra, over 2,600 kilometers (1,600 miles) away, and possibly in Thailand and Laos. Volcanic ash fell across Borneo, Sulawesi, Java, and Maluku islands. The mountain’s height dropped from about 4,300 to 2,850 meters (14,110 to 9,350 feet). At least 71,000 people died. The eruption caused global climate changes, leading to crop failures and famine in 1816.
Before 1815, Tambora was dormant for centuries as magma slowly built up. The magma chamber was filled with molten rock, and the surrounding rock was heated. By 1815, pressure had built up enough to cause a massive eruption.
The 1815 eruption had a VEI of 7, with energy 4–
Culture
In 2004, a human settlement destroyed by the Tambora eruption was discovered. That summer, a team led by Haraldur Sigurðsson, along with scientists from the University of Rhode Island, the University of North Carolina at Wilmington, and the Indonesian Directorate of Volcanology, began an archaeological dig at Tambora. Over six weeks, they found signs of human habitation about 25 kilometers (16 miles) west of the caldera, deep in the jungle, 5 kilometers (3.1 miles) from the shore. The team uncovered 3 meters (9.8 feet) of layers of pumice and ash. Scientists used ground-penetrating radar to locate a buried house that contained the remains of two adults, bronze bowls, ceramic pots, iron tools, and other artifacts. Tests showed that these items had been burned by the heat of the magma. Sigurðsson called the discovery the "Pompeii of the East," and media reports referred to it as the "Lost Kingdom of Tambora." Sigurðsson planned to return to Tambora in 2007 to search for other villages and possibly find a palace. Although many villages in the area had converted to Islam in the 17th century, the structures found so far do not show Islamic influence.
Based on artifacts such as bronze items and finely decorated pottery possibly from Vietnam or Cambodia, the team concluded that the people were wealthy traders. The Sumbawa people were known in the East Indies for their horses, honey, sappan wood (used for red dye), and sandalwood (used for incense and medicine). The area was thought to have very productive farming land.
The language of the Tambora people was lost with the eruption. Linguists studied old records, such as those by Zollinger and Raffles, and determined that Tambora was not an Austronesian language, as expected in the region, but may have been a language isolate or part of a Papuan language family found 500 kilometers (310 miles) or more to the east.
The eruption is described in later folklore as divine punishment. A local ruler is said to have angered Allah by giving dog meat to a pilgrim and killing him. This story is expressed in a poem written around 1830:
The noise was extremely loud. Torrents of water mixed with ash fell. Children and mothers screamed and cried, thinking the world had turned to ash. The cause was said to be the wrath of God Almighty because of the actions of the King of Tambora, who murdered a pilgrim and spilled his blood. This was done rashly and thoughtlessly.
Ecosystem
In 1847, a group led by Swiss botanist Heinrich Zollinger traveled to Sumbawa to study the area where a volcano had erupted and how it affected the environment. Zollinger was the first person to climb to the top of the mountain after the eruption, even though it was still covered in smoke. As he climbed, his feet sometimes sank into a warm layer of sulfur powder beneath a thin layer of soil. Some plants had started to grow again, such as trees on the lower slopes. A forest of Casuarina trees was found between 2,200 and 2,550 meters, and areas of Imperata cylindrica grass were also observed. In August 2015, a team from Georesearch Volcanedo Germany followed Zollinger’s path for the first time since 1847. The journey was difficult because of the long distance, high temperatures, and lack of water.
People began to return to the area in 1907, and a coffee plantation was built in Pekat village on the northwestern slope in the 1930s. A dense rainforest of Duabanga moluccana trees grew between 1,000 and 2,800 meters, covering up to 80,000 hectares. This rainforest was discovered in 1933 by a Dutch team led by Koster and de Voogd. They described the area as starting with dry, hot land and then entering a thick jungle with tall trees. At 1,100 meters, the trees became smaller. Above 1,800 meters, the area was dominated by Casuarina trees and Dodonaea viscosa flowering plants. Near the top, only a few Edelweiss and Wahlenbergia plants were found.
A survey in 1896 recorded 56 bird species, including the crested white-eye. Later studies found over 90 bird species, such as yellow-crested cockatoos, Zoothera thrushes, Hill mynas, green junglefowl, and rainbow lorikeets. These birds are hunted for the cagebird trade, and orange-footed scrubfowl are hunted for food. This hunting has caused some bird populations to decline, and the yellow-crested cockatoo is nearly extinct on Sumbawa.
A commercial logging company started operating in 1972, threatening the rainforest. The company was allowed to cut trees on 20,000 hectares, or 25% of the total area. Another part of the forest is used for hunting. Between the hunting area and the logging zone is a wildlife reserve where deer, water buffalo, wild pigs, bats, flying foxes, and other animals live. In 2015, the area protecting the mountain’s ecosystem was upgraded to a national park.
Zollinger (1847), van Rheden (1913), and W. A. Petroeschevsky (1947) could only see the caldera floor from the edge of the crater. In 2013, a German research team from Georesearch Volcanedo Germany completed the first long expedition into the caldera, which is about 1,300 meters deep. With the help of local guides, the team climbed down the southern wall of the caldera and reached the floor, facing extreme conditions. They stayed for nine days. Reaching the caldera floor is rare because the descent is dangerous and difficult, with risks like earthquakes, landslides, and rockfalls. Previous visits were short due to logistical challenges, making full studies impossible. The team’s research included studying effects of eruptions since 1815, measuring gases, observing plants and animals, and collecting weather data. They noted high activity from Doro Api Toi, a small volcano in the southern caldera, and gas escaping from the northern wall. The team discovered a new lavadome near Doro Api Toi, which they named “Adik Api Toi” (meaning “younger brother of Api Toi”). Later, Indonesians called it “Doro Api Bou” (meaning “new volcano”). This lavadome likely formed in 2011 or 2012 during increased seismic activity. In 2014, the same team returned for another expedition, spending over 12 days continuing their research.
Monitoring
Indonesia's population has grown quickly since the 1815 eruption. In 2020, the country had 270 million people, and 56% of them lived on the island of Java. The 1815 eruption would have affected about eight million people.
Seismic activity in Indonesia is watched by the Directorate of Volcanology and Geological Hazard Mitigation. Their monitoring post for Mount Tambora is in Doro Peti village. They use a seismograph to study seismic and tectonic activity. Since the 1880 eruption, there has been no major increase in seismic activity. Monitoring continues inside the caldera, with a focus on the parasitic cone Doro Api Toi.
The directorate made a disaster map for Mount Tambora. It divides areas near the volcano into two zones: a dangerous zone and a cautious zone. The dangerous zone includes areas directly affected by pyroclastic flows, lava flows, or pyroclastic falls. These areas include the caldera and its surroundings, covering up to 58.7 square kilometers (14,500 acres), where living is not allowed. The cautious zone includes areas that might be indirectly affected by lahar flows or pumice stones. This zone covers 185 square kilometers (46,000 acres) and includes Pasanggrahan, Doro Peti, Rao, Labuan Kenanga, Gubu Ponda, Kawindana Toi, and Hoddo villages. A river called Guwu, located on the southern and northwest sides of the mountain, is also part of the cautious zone.
Since mid-2025, volcanic activity, such as deep earthquakes, has increased. On March 10, 2026, the Center for Volcanology and Geological Hazard Mitigation (CVGHM/PVMBG) raised the alert level for Mount Tambora from level 1 to level 2 because of more deep volcanic earthquakes. People were told to stay at least 3 km away from Tambora. Activity included tectonic seismicity, deep volcanic seismicity (Type A/vulkanik dalam), and volcano-tectonic (VT) seismicity. In January 2026, 267 deep volcanic earthquakes were recorded. By February, the number increased to 453. This suggests magma is moving closer to the surface. Earthquake activity remained high in March. Between March 1-9, 88 earthquakes were recorded, along with rockfalls. No emissions were visible, but weather sometimes made viewing difficult.