Mount Tambora, or Tomboro, is an active stratovolcano in West Nusa Tenggara, Indonesia. Located on Sumbawa in the Lesser Sunda Islands, volcanism is the result of subduction zones. The 1815 eruption was the largest in recorded history, erupting up to 150 cubic kilometers of volcanic material, making it a VEI-7 on the Volcanic Explosivity Index. This caused the summer of 1816 to become known as the "Year Without a Summer" due to global cooling from the eruption.
Geographical setting
Mount Tambora is situated in the northern part of Sumbawa island, part of the Lesser Sunda Islands. It is a segment of the Sunda Arc, a chain of volcanic islands that make up the southern chain of the Indonesian archipelago. Tambora forms its own peninsula on Sumbawa, known as the Sanggar peninsula. To the north of the peninsula is the Flores Sea and to the south is the long and 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 interest to archaeologists and biologists. The mountain also attracts tourists for hiking and wildlife activities, though in small numbers. 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 routes of ascent to the caldera. The first begins at Doro Mboha village on the southeast of the mountain and follows a paved road through a cashew plantation to an elevation of . The road terminates at the southern part of the caldera, which at is reachable only by hiking. This location is only one hour from the caldera, and usually serves as a base camp from which volcanic activity can be monitored. The second route starts from Pancasila village at the northwest of the mountain and is only accessible on foot. The hike from Pancasila at elevation to the caldera of the volcano takes approximately 14 hours with several stops (pos) en route to the top. The trail leads through dense jungle with wildlife such as Elaeocarpus, Asian water monitor, reticulated python, hawks, orange-footed scrubfowl, pale-shouldered cicadabird (Coracina dohertyi), brown and scaly-crowned honeyeater, yellow-crested cockatoo, yellow-ringed white-eye, helmeted friarbird, wild boar, Javan rusa and crab-eating macaques.
History
Geological history Formation
Tambora lies north of the Java Trench system and above the upper surface of the active north-dipping subduction zone. Sumbawa Island is flanked to the north and south by oceanic crust. The convergence rate of the Australian Plate beneath the Sunda Plate is per year. Estimates for the onset of the volcanism at Mount Tambora range from 57 to 43 ka. The latter estimate published in 2012 is based on argon dating of the first pre-caldera lava flows. The formation of Tambora drained a large magma chamber pre-existing under the mountain. The Mojo islet was formed as part of this process in which Saleh Bay first appeared as a sea basin about 25,000 years ago.
A high volcanic cone with a single central vent formed before the 1815 eruption, which follows a stratovolcano shape. The diameter at the base is . The volcano frequently erupted lava, which descended over steep slopes. Tambora has produced trachybasalt and trachyandesite rocks which are rich in potassium. The volcanics contain phenocrysts of apatite, biotite, clinopyroxene, leucite, magnetite, olivine and plagioclase, with the exact composition of the phenocrysts varying between different rock types. Orthopyroxene is absent in the trachyandesites of Tambora.Foden, 1979, p. 49 Olivine is most present in the rocks with less than 53 percent SiO2, while it is absent in the more silica-rich volcanics, characterised by the presence of biotite phenocrysts.Foden, 1979, p. 50 The mafic series also contain titanium magnetite and the trachybasalts are dominated by anorthosite-rich plagioclase.Foden, 1979, p. 51 Rubidium, strontium and phosphorus pentoxide are especially rich in the lavas from Tambora, more than the comparable ones from Mount Rinjani.Foden, 1979, p. 56 The lavas of Tambora are slightly enriched in zircon compared with those of Rinjani.Foden, 1979, p.60
The magma involved in the 1815 eruption originated in the mantle and was further modified by melts derived from subducted sediments, fluids derived from the subducted crust and crystallization processes in magma chambers. 87Sr86Sr ratios of Mount Tambora are similar to those of Mount Rinjani, but lower than those measured at Sangeang Api. Potassium levels of Tambora volcanics exceed 3 weight percent, placing them in the shoshonite range for alkaline series.
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 lava flows. Thick scoria beds were produced by the fragmentation of lava flows. Within the upper section, the lava is interbedded with scoria, tuffs, pyroclastic flows and pyroclastic falls. Tambora has at least 20 parasitic cones and lava domes, including Doro Afi Toi, Kadiendi Nae, Molo and Tahe. The main product of these parasitic vents is basaltic lava flows.
Eruptive history
Radiocarbon dating has established that Mount Tambora had erupted three times during the current Holocene epoch before the 1815 eruption, but the magnitudes of these eruptions are unknown. Their estimated dates are 3910 BC ± 200 years, 3050 BC and 740 AD ± 150 years. An earlier caldera was filled with lava flows starting from 43,000 BC; two pyroclastic eruptions occurred later and formed the Black Sands and Brown Tuff formations, the last of which was emplaced between about 3895 BC and 800 AD.
In 1812, Mount Tambora became highly active, with its maximum eruptive intensity occurring in April 1815. The magnitude was 7 on the Volcanic Explosivity Index (VEI) scale, with a total tephra ejecta volume of up to 1.8 × 1011 cubic metres, or 180 cubic kilometres. Its eruptive characteristics included central vent and explosive eruptions, pyroclastic flows, tsunamis and caldera collapse. This eruption had an effect on global climate. Volcanic activity ceased on 15 July 1815. Activity resumed in August 1819—a small eruption with "flames" and rumbling aftershocks, and was considered to be part of the 1815 eruption. This eruption was recorded at 2 on the VEI scale.
Around 1880 ± 30 years, eruptions at Mount Tambora have been registered 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 and minor lava domes and flows were extruded on the caldera floor during the 19th and 20th centuries. The last eruption was recorded in 1967. It was a gentle eruption with a VEI of 0, which means it was non-explosive. Another very small eruption was reported in 2011. In August 2011, the alert level for the volcano was raised from level I to level II after increased activity was reported in the caldera, including earthquakes and steam emissions.
1815 eruption
Tambora underwent a series of violent eruptions, beginning on 5 April 1815, and culminating in the largest eruption in recorded human history. The magma chamber under Tambora had been drained by previous eruptions and lay dormant for several centuries as it refilled. Volcanic activity reached a peak that year, culminating in an explosive eruption that was heard on Sumatra island, more than away and possibly over away in Thailand and Laos. Heavy volcanic ash rains were observed as far away as Borneo, Sulawesi, Java, and Maluku Islands, and the maximum elevation of Tambora was reduced from about . Estimates vary, but the death toll was at least 71,000 people. The eruption contributed to global climate anomalies in the following years, while 1816 became known as the "year without a summer" because of the effect on North American and European weather. In the Northern Hemisphere, crops failed and livestock died, resulting in the worst famine of the century.
Chronology of the eruption Before 1815, Mount Tambora had been dormant for several centuries, as hydrous magma cooled gradually in a closed magma chamber. Inside the chamber, at depths of , cooling and partial crystallization of the magma exsolved high-pressure magmatic fluid. Overpressure of the chamber of about was generated as temperatures ranged from . In 1812, the crater began to rumble and generated a dark cloud.
A moderate-sized eruption on 5 April 1815 was followed by thunderous detonation sounds that could be heard in Ternate on the Molucca Islands, from Mount Tambora. On the morning of 6 April 1815, volcanic ash began to fall in East Java, with faint detonation sounds lasting until 10 April. What was first thought to be the sound of firing guns was heard on 10 and 11 April on Sumatra island (more than away), Cited by Oppenheimer (2003) and possibly over away in Thailand and Laos.
The eruptions intensified at about 7:00 p.m. on the 10th. Three plumes rose and merged. Pieces of pumice of up to in diameter rained down at approximately 8 p.m., followed by ash at around 9–10 p.m. The eruption column collapsed, producing hot pyroclastic flows that cascaded down the mountain and towards 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 veil of ash spread as far as West Java and South Sulawesi, while a "nitrous odor" was noticeable in Batavia. The heavy tephra-tinged rain did not recede until 17 April. Analysis of various sites on Mount Tambora using ground-penetrating radar has revealed alternations of pumice and ash deposits covered by the pyroclastic surge and flow sediments that vary in thickness regionally.
The eruption is estimated to have had a Volcanic Explosivity Index of 7. It had 4–10 times the energy of the 1883 Krakatoa eruption.Blast from the Past ; article; [July, 2002]; By Robert Evans; Smithsonian Magazine, online; accessed September 10, 2020 An estimated of pyroclastic trachyandesite was ejected, weighing approximately 1.4×1014 kg. This has left a caldera measuring across and deep. The density of fallen ash in Makassar was 636 kg/m3. Before the explosion, Mount Tambora was approximately high, one of the tallest peaks in the Indonesian archipelago. After the eruption of 1815, the maximum elevation was reduced to .
The 1815 Tambora eruption is the largest and most devastating observed eruption in recorded history; a comparison with other major eruptions is listed below. The explosion was heard or away, and ash deposits were registered at a distance of at least . A pitch of darkness was observed as far away as from the mountain summit for up to two days. Pyroclastic flows spread to distances of about from the summit and an estimated 9.3–11.8 × 1013 g of stratospheric sulfate aerosols were generated by the eruption.
Aftermath The island's entire vegetation was destroyed as uprooted trees, mixed with pumice ash, washed into the sea and formed rafts of up to 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.