Mount Tambora (or Tomboro) is an active stratovolcano on Sumbawa, one of the Lesser Sunda Islands of Indonesia. Sumbawa is flanked to the north and south by oceanic crust. It was formed due to the active subduction zones beneath it, and before its 1815 eruption, was more than 4,300 metres (14,100 feet) high, making it then one of the tallest peaks in the Indonesian archipelago.
The large magma chamber under Tambora had been drained by pre-1815 eruptions and underwent several centuries of dormancy as it refilled. Volcanic activity reached a peak that year, when Tambora erupted. With a Volcanic Explosivity Index of 7, the eruption was the largest since the Taupo eruption in 181 AD, and the largest in recorded history. The explosion was heard on Sumatra island, more than 2,000 kilometres (1,200 miles) away. Heavy volcanic ash rains were observed as far away as Borneo, Sulawesi, Java and Maluku islands, and Tambora was reduced to a height of 2,850 metres (9,350 feet). Although estimates vary, the death toll was at least 71,000 people, of which 11,000-12,000 were killed directly by the eruption. The eruption created global climate anomalies in the following years, while 1816 became known as the "year without a summer" due to the impact on North American and European weather. In the Northern Hemisphere, crops failed and livestock died, resulting in the worst famine of the century.
During a 2004 excavation, archaeologists discovered the remains of a civilization destroyed and buried by the 1815 eruption. Known as the "Pompeii of the East", the site has remained intact beneath three metres of pyroclastic deposits and provides insight into the culture that vanished. Today, Mount Tambora is closely monitored for volcanic activity; a powerful eruption would affect millions of Indonesians.
Video Mount Tambora
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 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 86 km (53.5 mi) long and 36 km (22 mi) 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 1,150 m (3,800 ft). The road terminates at the southern part of the caldera, which at 1,950 m (6,400 ft) 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.
Maps Mount Tambora
Geological history
Formation
Tambora is located 340 km (211 mi) north of the Java Trench system and 180-190 km (112-118 mi) 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 is 7.8 cm/year (3 in/year). The formation of Tambora is estimated to have begun around 57,000 years before present (BP). The formation of Tambora drained a large magma chamber under the mountain. The Mojo islet was formed as part of this geological process in which Saleh Bay first appeared as a sea basin (about 25,000 years BP).
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 60 km (37 mi). The volcano frequently erupted lava, which descended over steep slopes. Tambora has produced trachybasalt and trachyandesite rocks which are moderately rich in potassium. The volcanites contain phenocrysts of apatite, biotite, clinopyroxene, leucite, magnetite, olivine and plagioclase, although the exact composition of the phenocrysts varies between different rock types. 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.
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 1-4 m-thick (3.3-13.1 ft) 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 years BP; two pyroclastic eruptions occurred later and formed the Black Sands and Brown Tuff formations, the last of which was emplaced between about 3890 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 1.6 × 1011 cubic metres. Its eruptive characteristics included central vent and explosive eruptions, pyroclastic flows, tsunamis and caldera collapse. This eruption had a long-term 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, Tambora went into eruption again, but 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. 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 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 increasing activity was reported in the caldera, including earthquakes and steam emissions.
1815 eruption
Chronology of the eruption
Before 1815, Mount Tambora was dormant for several centuries as hydrous magma cooled gradually in a closed magma chamber. Inside the chamber, at depths of 1.5-4.5 kilometres (0.93-2.80 mi), cooling and partial crystallization of the magma exsolved high-pressure magmatic fluid. Overpressure of the chamber of about 4000-5000 bar was generated as temperature ranged from 700 °C-850 °C (1,300-1,500 °F). In 1812 the caldera 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 Makassar on Sulawesi (380 km or 236 mi), Batavia (now Jakarta) on Java (1,260 km or 783 mi) and Ternate on the Molucca Islands (1400 km or 870 mi). What was first thought to be the sound of firing guns was heard on 10-11 April on Sumatra island (more than 2,600 km or 1,615 mi away). On the morning of 6 April 1815 volcanic ash began to fall in East Java, with faint detonation sounds lasting until 10 April.
The eruptions intensified at about 7 p.m. on 10 April 1815. Three columns of "flame" rose and merged as the mountain became a flowing mass of "liquid fire". Pumice stones of up to 20 cm (8 in) wide rained down at approximately 8 p.m., followed by ash at around 9-10 p.m. Hot pyroclastic flows cascaded from the mountain to 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 finally recede until 17 April.
The eruption is estimated to have had a Volcanic Explosivity Index of 7. It had roughly four times the energy of the 1883 Krakatoa eruption. An estimated 100 km3 (38.6 mi3) of pyroclastic trachyandesite was ejected, weighing approximately 1.4×1014 kg. This has left a caldera measuring 6-7 km (4-5 mi) across and 600-700 m (2,000-2,300 ft) deep. The density of fallen ash in Makassar was 636 kg/m3. Before the explosion, Mount Tambora was approximately 4,300 m (14,000 ft) high, one of the tallest peaks in the Indonesian archipelago. After the explosion, it now measures only 2,851 m (9,300 ft).
The 1815 Tambora eruption is the largest observed eruption in recorded history (see Table I for comparisons). The explosion was heard 2,600 km (1,600 mi) away, and ash fell at least 1,300 km (800 mi) away. A pitch of darkness was observed as far away as 600 km (370 mi) from the mountain summit for up to two days. Pyroclastic flows spread to distances of about 20 km (12.5 mi) from the summit.
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 5 km (3 mi) 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.
A moderate tsunami struck the shores of various islands in the Indonesian archipelago on 10 April, with a height of up to 4 m (13 ft) in Sanggar at around 10 p.m. A tsunami of 1-2 m (3-6 ft) was reported in Besuki, East Java, before midnight and another exceeded 2 m (6 ft) in the Molucca Islands. The eruption column reached the stratosphere at an altitude of more than 43 km (140,000 ft). Coarser ash particles fell one to two weeks after the eruptions, while finer particles stayed in the atmosphere for months to years at an altitude of 10-30 km (33,000-100,000 ft). There are various estimates of the volume of ash emitted: a recent study estimates a dense-rock equivalent volume for the ash of 23 ± 3 cubic kilometres (5.52 ± 0.72 cu mi) and a dense-rock equivalent volume of 18 ± 6 cubic kilometres (4.3 ± 1.4 cu mi) for the pyroclastic flows. Longitudinal winds spread these fine particles around the globe, creating optical phenomena. Between 28 June and 2 July 1815 and 3 September and 7 October 1815, prolonged and brilliantly coloured sunsets and twilights were frequently seen in London, England. Most commonly, pink or purple colours appeared above the horizon at twilight and orange or red near the horizon.
The number of fatalities has been estimated by various sources since the nineteenth century. Zollinger (1855) numbered those directly killed at 10,000, mostly from pyroclastic flows. 38,000 died from starvation on Sumbawa island, and on Lombok 10,000 died from disease and hunger. Petroeschevsky (1949) estimated that about 48,000 and 44,000 people were killed on Sumbawa and Lombok, respectively. Several authors have used Petroeschevsky's figures, such as Stothers (1984), who estimated 88,000 deaths in total. However, Tanguy et al. (1998) considered Petroeschevsky's figures based on untraceable sources, so developed an estimate based solely on two primary sources: Zollinger, who spent several months on Sumbawa after the eruption, and the notes of Sir Stamford Raffles, Governor-General of the Dutch East Indies during the event. Tanguy pointed out that there may have been additional victims on Bali and East Java because of famine and disease, and estimated 11,000 deaths from direct volcanic action and 49,000 from post-eruption famine and epidemics. Oppenheimer (2003) estimated at least 71,000 deaths, and numbers as high as 117,000 have been offered.
Global effects
The 1815 eruption released 10 to 120 megatonnes of sulfur into the stratosphere, causing a global climate anomaly. Different methods have been used to estimate the ejected sulfur mass: the petrological method, an optical depth measurement based on anatomical observations, and the polar ice core sulfate concentration method, which calibrated against cores from Greenland and Antarctica.
In the spring and summer of 1816, a persistent stratospheric sulfate aerosol veil, described then as a "dry fog", was observed in the northeastern United States. It was not dispersed by wind or rainfall, and it reddened and dimmed sunlight to an extent that sunspots were visible to the naked eye. Areas of the northern hemisphere suffered extreme weather conditions and 1816 became known as the "year without a summer". Average global temperatures decreased about 0.4-0.7 °C (0.7-1.3 °F), enough to cause significant agricultural problems around the globe. After 4 June 1816, when there were frosts in Connecticut, cold weather expanded over most of New England. On 6 June 1816, it snowed in Albany, New York and Dennysville, Maine. Similar conditions persisted for at least three months, ruining most crops across North America while Canada experienced extreme cold. Snow fell until 10 June near Quebec City, accumulating to 30 cm (12 in).
That year became the second-coldest year in the northern hemisphere since 1400, while the 1810s were the coldest decade on record, a result of Tambora's eruption and other suspected volcanic events between 1809 and 1810. (See sulfate concentration chart.) Surface-temperature anomalies during the summers of 1816, 1817 and 1818 were -0.51, -0.44 and -0.29 °C, respectively. Along with a cooler summer, parts of Europe experienced a stormier winter.
This climate anomaly has been cited as a reason for the severity of the 1816-19 typhus epidemic in southeast Europe and the eastern Mediterranean. In addition, large amounts of livestock died in New England during the winter of 1816-1817, while cool temperatures and heavy rains led to failed harvests in the British Isles. Families in Wales travelled long distances as refugees, begging for food. Famine was prevalent in north and southwest Ireland, following the failure of wheat, oat and potato harvests. The crisis was severe in Germany, where food prices rose sharply. Demonstrations at grain markets and bakeries, followed by riots, arson and looting, took place in many European cities. It was the worst famine of the 19th century.
Culture
A human habitation obliterated by the Tambora eruption was discovered in 2004. That summer, a team led by Haraldur Sigurðsson 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 in Tambora. Over six weeks, they unearthed evidence of habitation about 25 km (15.5 mi) west of the caldera, deep in jungle, 5 km (3 mi) from shore. The team excavated 3 m (10 ft) of deposits of volcanic pumice and ash. The scientists used ground-penetrating radar to locate a small buried house which contained the remains of two adults, bronze bowls, ceramic pots, iron tools and other artefacts. Tests revealed that carbonized objects had been carbonized by the heat of the magma. Sigurdsson dubbed the find the "Pompeii of the East", and media reports referred to the "Lost Kingdom of Tambora". Sigurdsson intended to return to Tambora in 2007 to search for the rest of the villages, and hopefully to find a palace. Many villages in the area had converted to Islam in the 17th century, but the structures uncovered so far do not show Islamic influence.
Based on the artefacts found, such as bronzeware and finely decorated china possibly of Vietnamese or Cambodian origin, the team concluded that the people were well-off traders. The Sumbawa people were known in the East Indies for their horses, honey, sappan wood (for producing red dye), and sandalwood (for incense and medications). The area was thought to be highly productive agriculturally.
The language of the Tambora people was lost with the eruption. Linguists have examined remnant lexical material, such as records by Zollinger and Raffles, and established that Tambora was not an Austronesian language, as would be expected in the area, but possibly a language isolate, or perhaps a member of one of the families of Papuan languages found 500 kilometres (310 mi) or more to the east.
The eruption is captured in latter-day folklore, which explains the cataclysm in terms of divine retribution. A local ruler is said to have incurred the wrath of Allah by feeding dog meat to a hajji and killing him. This is expressed in a poem written around 1830:
Ecosystem
A team led by the Swiss botanist Heinrich Zollinger arrived on Sumbawa in 1847. Zollinger sought to study the area of eruption and its effects on the local ecosystem. He was the first person after the eruption to ascend the summit, which was still covered by smoke. As Zollinger climbed, his feet sank several times through a thin surface crust into a warm layer of powder-like sulfur. Some vegetation has regrown, including trees on the lower slope. A Casuarina forest was noted at 2,200-2,550 m (7,200-8,400 ft), while several Imperata cylindrica grasslands were also found.
Rehabitation of the area began in 1907, and a coffee plantation was established in the 1930s in the Pekat village on the northwestern slope. A dense rain forest of Duabanga moluccana trees had grown at an altitude of 1,000-2,800 m (3,300-9,000 ft). It covers an area up to 80,000 hectares (800 km²). The rain forest was discovered 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), the trees became thinner in shape. Above 1,800 m (6,000 ft), they found Dodonaea viscosa flowering plants dominated by Casuarina trees. On the summit was sparse Edelweiss and Wahlenbergia.
A 1896 survey records 56 species of birds including the Crested White-eye. Several other zoological surveys followed and found other bird species, with over 90 bird species discoveries in this period, including 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 population declines, and the Yellow-crested Cockatoo is nearing extinction on Sumbawa island.
A commercial logging company began to operate in the area in 1972, posing a threat to the rain forest. The company holds a timber-cutting concession for an area of 20,000 hectares (200 km²), 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 species of reptiles and birds can be found. In 2015, the conservation area protecting the mountain's ecosystem was upgraded to a national park.
Monitoring
Indonesia's population has been increasing rapidly since the 1815 eruption. As of 2010, the population has reached 238 million people, of which 57.5% are concentrated on the island of Java. An event as significant as the 1815 eruption would impact about eight million people.
Seismic activity in Indonesia is monitored by the Directorate of Volcanology and Geological Hazard Mitigation with the monitoring post for Mount Tambora located at Doro Peti village. They focus on seismic and tectonic activities by using a seismograph. There has been no significant increase in seismic activity since the 1880 eruption. Monitoring is continuously performed inside the caldera, with a focus on the parasitic cone Doro Api Toi.
The directorate created a disaster mitigation map for Mount Tambora, which designates two zones for an eruption: a dangerous zone and a cautious zone. The dangerous zone identifies areas that would be directly affected by pyroclastic flows, lava flows or pyroclastic falls. It includes areas such as the caldera and its surroundings, a span of up to 58.7 square kilometres (14,500 acres) where habitation is prohibited. The cautious zone consists of land that might be indirectly affected, either by lahar flows and other pumice stones. The size of the cautious area is 185 square kilometres (46,000 acres), and includes Pasanggrahan, Doro Peti, Rao, Labuan Kenanga, Gubu Ponda, Kawindana Toi and Hoddo villages. A river, called Guwu, at the southern and northwest part of the mountain is also included in the cautious zone.
Panorama
References
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. Archived from the original on 2 July 2007.
- "Tambora". Global Volcanism Program. Smithsonian Institute.
- WikiSatellite view at WikiMapia
- Google Earth view
Source of the article : Wikipedia
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