The 1257 Samalas eruption was a major eruption of the Samalas volcano, next to Mount Rinjani on Lombok Island in Indonesia. The eruption left behind a large caldera next to Rinjani, with Lake Segara Anak inside it. This eruption probably had a Volcanic Explosivity Index of 7, making it one of the largest eruptions of the current Holocene epoch.
An examination of ice cores showed a large spike in sulfate deposition around 1257. This was strong evidence of a large eruption having occurred somewhere in the world. In 2013, scientists proved that the eruption occurred at Mount Samalas.
This eruption had four distinct phases, alternately creating eruption columns reaching tens of kilometres into the atmosphere and pyroclastic flows burying large parts of Lombok Island. The flows destroyed human habitations, including the city of Pamatan. Ash from the eruption fell as far away as Java Island. The volcano deposited more than 10 cubic kilometres (2.4 cu mi) of material. The eruption was witnessed by people who recorded it on palm leaves, the Babad Lombok. Later volcanic activity created additional volcanic centres in the caldera, including the Barujari cone that remains active.
The aerosols injected into the atmosphere reduced the solar radiation reaching the Earth's surface, which cooled the atmosphere for several years and resulting in famines and crop failures in Europe and elsewhere, although the exact scale of the temperature anomalies and their consequences is still debated. It is possible that the eruption helped trigger the Little Ice Age.
Video 1257 Samalas eruption
Geology
General geology
Samalas and Mount Rinjani are in the Sunda Arc, a subduction zone where the Australian plate subducts beneath the Eurasian plate. The magmas feeding Samalas and Rinjani probably form from peridotites in the mantle wedge beneath Lombok Island. Other volcanoes in the region include Agung and Batur plus Bratan on the island of Bali to the west. Before the eruption, Samalas may have been as high as 4,200 ± 100 metres (13,780 ± 330 ft). This estimate is based on reconstructions such as continuing upwards from its surviving lower slopes.
The oldest geological units on Lombok Island are from the Oligocene-Miocene, with old volcanic units cropping out in southern Lombok. Before 12,000 BP, volcanic activity built up the Samalas volcano. During a phase between 11,940±40 and 2,550±50 BP the Rinjani volcano formed; this last eruption generated the Rinjani pumice with a volume of 0.3 cubic kilometres (0.072 cu mi) dense rock equivalent and thicknesses of 6 centimetres (2.4 in) at 28 kilometres (17 mi) distance, although later research suggests that this eruption may have occurred on Samalas instead. Another eruption took place between 5,990 ± 50 and 2,550 ± 50 BP forming the Propok Pumice with a dense rock equivalent volume of 0.1 cubic kilometres (0.024 cu mi). More eruptions are dated 11,980±40, 11,940±40, 6250±40 BP, and continued until about 500 years before 1257. Then, a large caldera-forming eruption destroyed Samalas volcano. Later volcanic activity occurred in the Segara Anak caldera, forming the Segara Munac, Rombogan, and Barujari volcanoes. Of these, most volcanic activity occurs in the Barujari volcano with eruptions in 1884, 1904, 1906, 1909, 1915, 1966, 1994, 2004, and 2009. Rombogan was active in 1944. Volcanic activity mostly consists of explosive eruptions and ash flows.
The rocks of the volcano are mostly dacitic, SiO
2 contents range between 62-63 percent by weight. Volcanic rocks in the Banda arc are mostly calc-alkaline ranging from basalt over andesite to dacite. The volcano rests on crust of about 20 kilometres (12 mi) thickness, and the lower extremity of the Wadati-Benioff zone is about 164 kilometres (102 mi) deep.
Eruption
The eruption of 1257 occurred probably during September. Based on the deposits of the eruption, it commenced with a first phreatic (steam explosion powered) stage that deposited 3 centimetres (1.2 in) of ash over 400 square kilometres (150 sq mi) of northwest Lombok Island. In the subsequent first magmatic stage, lithic-rich pumice rained down, the pumice fallout reaching a thickness of 8 centimetres (3.1 in) both upwind on East Lombok and on Bali. Subsequently, various phases of lapilli rock and ash fallout occurred, as well as pyroclastic flows that were partially confined within the valleys on Samalas's western flank. Some ash deposits were eroded by the pyroclastic flows, generating furrow structures in the ash deposits. Pyroclastic flows even crossed the Bali Sea, reaching the Gili Islands. This eruption phase was probably phreatomagmatic, as the deposits show evidence of interaction of the lava with water. Three pumice fallout episodes subsequently occurred, which covered the widest extent of all deposits formed by the eruption. These pumices fell as far as Sumbawa in the east, where they were up to 7 centimetres (2.8 in) thick.
The emplacement of these pumices was followed by another stage of pyroclastic flow activity, probably caused by the collapse of the eruption column which generated the flows and the beginning of the formation of the caldera, where the conditions of the eruption changed from column-generating to fountain-generating. These pyroclastic flows were deflected by the topography as they flowed across the island incinerated the island's vegetation. Interaction between these flows and the air triggered the formation of additional eruption clouds and secondary pyroclastic flows. Where the flows entered the sea north and east of Lombok Island, steam explosions generated pumice cones on the beach and additional secondary pyroclastic flows. These pyroclastic flows had an on-land volume of 29 cubic kilometres (7.0 cu mi), and reached thicknesses of 35 metres (115 ft) as far away as 25 kilometres (16 mi) from Samalas. These phases are also known as P1 (phreatic and first magmatic phase), P2 (phreatomagmatic with pyroclastic flows), P3 (plinian) and P4 (pyroclastic flows). The whole eruption lasted between 12 and 15 hours, not accounting for the first emission of pyroclastic flows (P2).
Tephra from the eruption fell as far as Java, forming part of the so-called Muntilan Tephras which were found on the slopes of other volcanoes of Java, but could not be linked to eruptions to these volcanic systems. These tephras reach thicknesses of 2-3 centimetres (0.79-1.18 in) on Mount Merapi, 15 centimetres (5.9 in) on Mount Bromo, 22 centimetres (8.7 in) at Ijen and 12-17 centimetres (4.7-6.7 in) on Agung volcano on Bali. In Lake Logung on Java it was 3 centimetres (1.2 in) thick. Most of the tephra was deposited west-southwest of Samalas. Considering the thickness of Samalas tephras found at Mount Merapi, the total volume may have reached 32-39 cubic kilometres (7.7-9.4 cu mi). The dispersal index (the surface area covered by an ash or tephra fall) of the eruption reached 7,500 square kilometres (2,900 sq mi) during the first stage and 110,500 square kilometres (42,700 sq mi) during the third stage, implying that it was a Plinian eruption and an ultraplinian eruption respectively.
The eruption column from this eruption reached a height of 39-40 kilometres (24-25 mi) at windspeeds of 10 metres per second (33 ft/s) during the first stage (P1), and 43-38 kilometres (27-24 mi) between (P3) the two stages with emission of pyroclastic flows. This eruption column was high enough that SO
2 in it and its S isotope ratio was influenced by photolysis at high altitudes.
Various volumes have been estimated for the various stages of the Samalas eruption. The first stage reached a volume of 12.6-13.4 cubic kilometres (3.0-3.2 cu mi). The second phreatomagmatic phase has been estimated to have had a volume of 0.9-3.5 cubic kilometres (0.22-0.84 cu mi). The total dense rock equivalent volume of the whole eruption was at least 40 cubic kilometres (9.6 cu mi). The material erupted by the volcano had a temperature of about 1,000 °C (1,830 °F). Compositionally, the material was of trachydacitic composition, containing amphibole, apatite, clinopyroxene, iron sulfide, orthopyroxene, plagioclase, and titanomagnetite. It formed out of basaltic magma by fractional crystallization. Either the entry of new magma into the magma chamber or the effects of gas bubble buoyancy have been proposed as mechanisms that triggered the eruption.
The eruption had a volcanic explosivity index of 7, making it one of the largest eruptions of the current Holocene epoch. It was stronger than the eruptions of Mount Tambora in 1815 and Krakatoa in 1883. Eruptions of comparable intensity include the Kurile lake eruption in the 7th millennium BC, the Mount Mazama eruption in the 6th millennium BC, the Minoan eruption, and the Tierra Blanca Joven eruption of Lake Ilopango in the 6th century. Pumice falls with a fine graining and colour of cream from the Samalas eruption form a useful tephrochronological wikt:marker on Bali. Tephra from the volcano was found in ice cores as far as 13,500 kilometres (8,400 mi) away from Samalas, and a tephra layer sampled at Dongdao island in the South China Sea has been tentatively linked to Samalas.
The eruption left the Segara Anak caldera, which has a diameter of 6-7 kilometres (3.7-4.3 mi), where the Samalas mountain was before; before the eruption the mountain was probably about 4,193 ± 93 metres (13,757 ± 305 ft) high. Within its 700-2,800 metres (2,300-9,200 ft) high walls, a 200 metres (660 ft) deep crater lake formed. The Barujari cone rises 320 metres (1,050 ft) above the water of the lake and has had 15 eruptions since 1847. A crater lake may have already existed on Samalas before the eruption and supplied its phreatomagmatic phase with 0.1-0.3 cubic kilometres (0.024-0.072 cu mi) of water. Alternatively, the water could have come from aquifers. A collapse structure cuts into Rinjani's slopes facing the Samalas caldera.
The eruption that formed the caldera was first recognized in 2003, and in 2004 a volume of 10 cubic kilometres (2.4 cu mi) was attributed to this eruption. Early research considered that the caldera-forming eruption occurred between 1210 and 1300. In 2013, Lavigne suggested that the eruption occurred in May-October 1257, resulting in the climate changes of 1258. Presently, a number of villages on Lombok are constructed on the pyroclastic flow deposits from the 1257 event.
Maps 1257 Samalas eruption
Research history
A major volcanic event in 1257-1258 was identified from data in ice cores and from medieval records in the northern hemisphere. The sulfur deposits in the polar ice caps had already showed that climate disturbances reported in that time were due to a volcanic event, with the global spread indicating a tropical volcano as the cause, although at first a source in a volcano near Greenland had been considered. The spike in sulfate concentrations was first observed in the Crête ice core, associated with a deposition of rhyolitic ash. These ice cores indicated a large sulfate spike around 1257, the largest in 7,000 years and twice the size of the 1815 eruption of Tambora sulfate spike, but later-discovered sulfate spikes around 44 BC and 426 BC rival its size. This discovery was made in the 1980s. In 2003, a dense rock equivalent volume of 200-800 cubic kilometres (48-192 cu mi) was estimated for this eruption, but it was also proposed that the eruption might have been somewhat smaller and enriched in sulfur. The volcano responsible could not be identified at first; Tofua volcano in Tonga was proposed at first but dismissed, as the Tofua eruption was too small to generate the 1257 sulfate spikes. Likewise, a volcanic eruption in 1256 at Harrat al-Rahat near Medina was too small to trigger these events. Other proposals included several simultaneous eruptions. Estimated caldera diameters ranged 10-30 kilometres (6.2-18.6 mi).
The suggestion that Samalas/Rinjani might be the source volcano was first made in 2012, since the other candidate volcanoes - El Chichon and Quilotoa - did not match the chemistry of the sulfur spikes. El Chichon and Quilotoa and Okataina were also inconsistent with the timespan and size of the eruption. The conclusive link between these events and an eruption of Samalas was made in 2013 on the basis of historical records in Indonesia: the Babad Lombok, writings in Old Javanese on palm leaves, written in the 13th century, induced Franck Lavigne, who had already suspected that a volcano on Lombok may be responsible, to conclude that the Samalas volcano was responsible.
All houses were destroyed and swept away, floating on the sea, and many people died
This event occurred before the end of the 13th century. The role of the Samalas eruption in the global climate events was confirmed by comparing the geochemistry of glass shards found in ice cores to that of the eruption deposits on Lombok.
Search for geological evidence of these events was helped by many exposures and cross-sections of volcanic ash deposits which were caused by men bulk-quarrying them for construction material.
Climate effects
Ice cores in the northern and southern hemisphere display sulfate spikes associated with Samalas, the signal being the strongest in the southern hemisphere for the last 1000 years and being only exceeded by Laki's signal in the northern; one reconstruction even considers it the strongest of the last 2500 years. In addition, ice cores from Illimani in Bolivia contain sulfate spikes from the eruption. For comparison, the 1991 eruption of Pinatubo ejected only about a tenth of Samalas's sulfur. Sulfate deposition from the Samalas eruption has been noted at Svalbard, and the fallout of sulfuric acid from the volcano may have directly affected peatlands in northern Sweden. The amount of SO
2 released by the eruption has been estimated to be 158,000,000 ± 12,000,000 tonnes (156,000,000 ± 12,000,000 long tons; 174,000,000 ± 13,000,000 short tons); the mass release was increased in comparison with the Tambora eruption due to a more effective injection of tephra into the stratosphere and/or higher sulfur contents of the Samalas magma.
When large scale volcanic eruptions inject aerosols into the atmosphere, they can form stratospheric veils, which reduce the amount of light reaching the surface. That reduces the temperatures on much of the Earth and can cause problems in agriculture including famine. The social effects of such events, however, are often reduced by the resilience of humans. Not all years with cold summers are linked to volcanic activity. Volcanic eruptions can also deliver bromine and chlorine into the stratosphere, where they contribute to the breakdown of ozone. While most of them would have been removed by scavenging by the eruption column, the quantities that have been modelled for the Samalas halogen release (227,000,000 ± 18,000,000 tonnes (223,000,000 ± 18,000,000 long tons; 250,000,000 ± 20,000,000 short tons) of chlorine and up to 1,300,000 ± 300,000 tonnes (1,280,000 ± 300,000 long tons; 1,430,000 ± 330,000 short tons) of bromine would have reduced the stratospheric ozone.
Samalas, along with the Kuwae eruption in the 1450s and Tambora in 1815, was one of the strongest cooling events in the last millennium, even more so than at the peak of the Little Ice Age. The effects of the Samalas eruption form the strongest volcanic signal in boreholes of the Urals. After an early warm winter 1257-1258 (winter warming is frequently observed after tropical volcanic eruption), resulting in the early flowering of violets according to reports from France, European summers were colder after the eruption, and winters were long and cold.
According to earlier reconstructions, summer cooling reached 0.69 K (1.24 °F) in the Southern Hemisphere and 0.46 K (0.83 °F) in the Northern Hemisphere. More recent proxy data have indicated that a temperature drop of 0.7 °C (1.3 °F) occurred in 1258 and of 1.2 °C (2.2 °F) in 1259, but with differences between various geographical areas. For comparison, the radiation forcing of Pinatubo's 1991 eruption was about a seventh of that of the Samalas eruption. Sea surface temperatures likewise decreased by 0.3-2.2 °C (0.54-3.96 °F), triggering changes in the ocean circulations and in the formation of deep water. Temperature changes may have lasted for a decade. Precipitation and evaporation both decreased as well, but the decrease of evaporation was stronger.
The Samalas signal, however, is only inconsistently reported from tree ring climate information, and the temperature effects were likewise limited, probably because the large sulfate output altered the average size of particles and thus their radiation forcing. Climate modelling indicated that the Samalas eruption may have reduced global temperatures by approximately 2 °C (3.6 °F), a value largely not replicated by proxy data. Better modelling indicated that the principal temperature anomaly occurred in 1258 and continued until 1261. Climate models tend to overestimate the climate impact of a volcanic eruption; one explanation is that climate models tend to assume that aerosol optical depth increases linearly with the quantity of erupted sulfur. The possible occurrence of an El Nino before the eruption may have further reduced the cooling.
The Samalas eruption together with another eruption in the 14th century set off a growth of ice caps and sea ice, and glaciers in Norway advanced. It might also have modified the North Atlantic oscillation, causing it to acquire more negative values in the subsequent decades in co-operation with a beginning decrease in solar activity as part of the Wolf minimum in the solar cycle. The advances of ice after the Samalas eruption may have strengthened and prolonged the climate effects. Later volcanic activity in 1269, 1278, and 1286 and the effects of sea ice on the North Atlantic would have further contributed to ice expansion. The glacier advances triggered by the Samalas eruption are documented on Baffin Island, where vegetation killed by the advancing ice was conserved in it. Likewise, a change from a warm climate phase to a colder one, in Arctic Canada, coincides with the Samalas eruption.
The Samalas eruption came after the Medieval Climate Anomaly and at a time where a period of climate stability was ending, with prior eruptions in 1108, 1171, and 1230 already having upset global climate. Subsequent time periods displayed increased volcanic activity until the early 20th century. The time period 1250-1300 was heavily disturbed by volcanic activity, and is recorded by a moraine from a glacial advance on Disko Island, although the moraine may indicate a pre-Samalas cold spell. These volcanic disturbances along with positive feedback effects from increased ice may have started the Little Ice Age even without the need for changes in solar radiation, but this theory is controversial.
The eruption left traces, including decreased tree growth in Mongolia between 1258-1262 based on tree ring data, and a very wet monsoon in Vietnam. Another effect of the eruption-induced climate change may have been a brief decrease of atmospheric CO
2. Cooling may have lasted for 4-5 years based on simulations and tree ring data.
Other regions such as Alaska were mostly unaffected. There is little evidence that tree growth was affected in Fennoscandia, Quebec, and the Western United States. In the case of Alaska, possibly the climate effect was moderated by the nearby ocean. In 1259 on the other hand western Europe and the west coastal North America displayed mild weather.
Among the effects estimated from analysis are the most negative Southern Annular Mode excursion of the last millennium, as well as a weakening of the atlantic meridional overturning circulation which lasted long after the eruption, possibly aiding in the onset of the Little Ice Age as well.
Social and historical consequences
This eruption led to global disaster in 1257-1258.
Lombok Kingdom (Indonesia)
Western and central Indonesia were dominated by many kingdoms in competition with each other, and they often built temple complexes with inscriptions documenting certain kinds of historical events; however very little direct historical evidence of the consequences of the Samalas eruption exists. The Babad Lombok describe how villages on Lombok were destroyed during the middle 13th century by ash and high-speed sweeps of gas and rocks, and is also the source of the name "Samalas". The city of Pamatan, capital of a kingdom on Lombok, was destroyed along with the kingdom by the eruption and disappeared from history, although the royal family survived according to the Javanese text, and there is no clear cut evidence that the kingdom itself was destroyed by the eruption. Thousands of people died during the eruption. Bali and Lombok Island may have been depopulated by the eruption, possibly for generations, allowing Kertanegara to conquer Bali in 1284 with little resistance.
Europe
The consequences of the Samalas eruption have been analyzed thanks to contemporary chronicles in Europe, which documented anomalous weather conditions in 1258. Reports in 1258 in France and England indicate a dry fog, giving the impression of a persistent cloud cover to contemporary observers. Medieval chronicles say that in 1258, the summer was cold and rainy, causing floods and bad harvests, with cold from February to June. In Europe and the Middle East, changes in atmospheric colours, storms, cold, and severe weather were reported in 1258-1259. In Europe, excess rain and cold and high cloudiness damaged crops and caused famines followed by epidemics, although 1258-1259 did not lead to famines as bad as some later ones like the Great Famine of 1315-17. In northwest Europe, the effects included crop failure, famine, and weather changes. Crop failures and a famine in London have been linked to this event. Witnesses reported a death toll of 15,000 to 20,000 in London. A mass burial of famine victims was found in the 1990s in the centre of London. Matthew Paris of St Albans described how until mid-August in 1258, the weather alternated between cold and strong rain, causing high mortality.
Swollen and rotting in groups of five or six, the dead lay abandoned in pigsties, on dunghills, and in the muddy streets.
The resulting famine was severe enough that grain was imported from Germany and Holland. The price for cereal increased in Britain, France, and Italy. Outbreaks of disease occurred during this time in the Middle East and England. With and after the winter of 1258-9, exceptional weathers were reported less commonly, but the winter of 1260-1 was very severe in Iceland, Italy, and elsewhere.
Byzantine Empire
Potential long term consequences of the eruption were the Byzantine Empire losing control over western Anatolia, resulting from a shift in the political power from Byzantine farmers to mostly Turkoman pastoralists in the area. The origins of the Flagellante movement may also be the social distress triggered by the eruption, but warfare and other plights may have contributed.
Northeast Asia
Problems were also recorded in China, Japan, and Korea; in Japan, the Mirror of the East chronicle from Azuma Kagami mentions that rice paddies and gardens were destroyed by the cold and wet weather, and the Shoga famine may have been aggravated by bad weather in 1258 and 1259. Other effects of the eruption include a total darkening of the Moon in May 1258 during a lunar eclipse.
See also
- Massive explosive eruptions
References
Sources
External links
- Mass grave in London reveals how volcano caused global catastrophe
- Google Earth view of the north of Lombok including Rinjani and the caldera
Source of the article : Wikipedia
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