Eruption of the Samala in 1257

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The outbreak of Samalas 1257 was a huge volcanic eruption of the next to the Rinjani located stratovolcano Samalas on the Indonesian island of Lombok . The effects on the world climate were catastrophic.

introduction

The Segara Anak crater lake created by the eruption

The eruption reached magnitude 7 on the Volcanic Explosion Index (VEI) and left behind a huge crater lake , the Segara Anak . It was one of the strongest eruptions in the entire Holocene, with the largest volcanic sulfur deposition in the last 2000 years. Its existence could be determined by means of ice cores , which show a maximum in the sulphate concentration in 1259 . In 2013, historical records indicating the disaster were discovered.

The eruption took place in four stages, the ash columns of which always reached into the stratosphere and, by means of pyroclastic currents , buried large parts of Lombok under them and, among other things, wiped out the city of Pamatan. The ash rain even reached Java . The total volume of tephra expelled was 33 to 40 cubic kilometers of dense rock equivalent ( DRE ). Later volcanic episodes created further volcanic centers within the caldera , including the Barujari cone, which is still active today.

The outbreak was observed by people on the neighboring islands who recorded their knowledge on palm leaf manuscripts . The aerosols thrown into the atmosphere by the volcano reduced solar radiation worldwide and conjured up a volcanic winter that would last for several years.

geology

The volcanoes of Indonesia. The Sunda Arc stretches from Sumatra via Java to Timor.

The Samalas and Rinjani volcanoes are located in the eastern Sunda Arc . They sit on a subduction zone where the Australian plate dips beneath the Eurasian plate at a rate of 7 centimeters / year in a north direction. Their magmas probably emerged from peridotites of the mantle wedge below Lombok . Neighboring volcanoes are the Gunung Agung , Gunung Batur and Bratan on Bali further west. Based on reconstructions, it is assumed that the Samalas reached a height of 4200 ± 100 meters and thus represented a giant volcano.

General geology

The general geological conditions on Lombok were mapped in 1994 by Mangga and colleagues. The oldest geological deposits date from the late Oligocene and early Miocene and form the Pengulung Formation . This is overlaid by the Kawangan Formation of the Middle Miocene. Both formations were interspersed with Dazites and basalts in the Middle Miocene and partly changed with contact metamorphosis. Above it then follows the Ekas formation from the late Miocene. The three formations are in the south of Lombok and form a hilly landscape there. The Lombok Volcanic Group then lies over these older formations with the Kali-Palung Formation , which in turn is covered discordantly by volcanic rocks of the Quaternary , which were most likely mined by the Pusuk , Nangi and Samalas / Rinjani volcanoes . The most recent are alluvial sediments of the coastal area.

The volcanic activities at the Samalas / Rinjani volcanic complex can be divided into five stages:

  • Pre- stratovolcano stage
  • Stratovolcano stage
  • Low activity stage
  • Syn caldera stage
  • Post-caldera stage

During the pre-stratovolcanic stage 12,000 years ago BP , the Samalas volcano grew before the beginning of the Holocene ; he is also known as the Old Rinjani.

The Rinjani is younger and formed between 11,980 ± 40 and 5990 ± 50 years BP during the stratovolcano stage in the eastern flank of the Samala. The low activity stage is 2,550 ± 50 years BP. The last eruption on the Rinjani produced the Rinjani pumice with a volume of 0.3 cubic kilometers DRE . Rinjani eruptions are known for 11,980 ± 40, 11,940 ± 40, and 6250 ± 40 years BP. A major eruption on the Rinjani between 5990 ± 50 and 2550 ± 50 years BP deposited 0.1 cubic kilometers of DRE of "Propok pumice".

During the syn caldera stage, the eruption of 1257 took place, which completely destroyed the Samalas volcano and left behind an east-west oriented, 8.5 × 6 kilometer collapse caldera, the 800 meter deep Segara Anak. Subordinate eruptions took place in it during the later post-Caldera stage, the small volcanic cones such. B. built the Segara Munac (on the western flank of the Rinjani), Rombogan, Anak Barujari and Barujari. Most of the volcanic activity was concentrated on the Barujari, which erupted in 1884, 1904, 1906, 1909, 1915, 1966, 1994, 2004 and 2009. The Rombogan was active in 1944. These were mainly explosive eruptions and streams of ash. The last eruption on Barujari occurred in December 2015.

geochemistry

In terms of their chemical composition, the rock masses extracted from the Samalas eruption are predominantly of a Dacite nature. Their SiO 2 content varies between 62 and 63 percent by weight. The younger deposits on the Barujari are far less differentiated, porphyry , basaltic andesites with a significantly lower SiO 2 content of 53 to 55 percent by weight.

The volcanic rocks in the Sunda Banda arc are generally typical island arc volcanics with predominantly calcareous to high-K- calcareous chemistry and contain basalts , andesites and dazites. In addition to these rocks of the calcareous main series, J. D. Foden could also recognize a separately developing side line consisting of ankaramites and basalts with a high aluminum content.

The earth's crust below the Samalas volcano is around 20 kilometers thick and the Wadati-Benioff zone is around 164 kilometers deep.

Geochemically , the volcanic rocks of the Samalas complex can be divided into two groups:

  • Stratovolcanic and post-caldera volcanic rocks
  • Vulcanites of the low activity and caldera stages.

The volcanic rocks of the stratovolcanic stage are basaltic andesites with an SiO 2 content between 44.8 and 63.7 percent by weight. The post- caldera volcanic rocks are olivine - pyroxene- andesites with an SiO 2 content of around 55 percent by weight. According to Nakagawa and colleagues (2015), the Dazitic magma of the stage of low activity and the actual caldera explosion could not have emerged from a basaltic starting magma through fractional crystallization alone , but also had to have crustal melting and / or AFC processes (assimilation / fractional crystallization). have experienced.

outbreak

Topography of Lombok; the caldera Segara Anak des Samalas is located in the central northern part of the island.

The eruption probably took place in September of 1257. As the deposits show, he began with an initial phreatic phase that distributed three centimeters of ash over 400 square kilometers in northwestern Lombok. The first igneous phase that followed produced eight centimeters of rock- rich pumice ash in eastern Lombok and Bali.

Afterwards, lapilli and ashes were rained off in several phases and the first pyroclastic flows arose. They were mainly limited to the valleys on the western flank and eroded furrows here in previously delivered ashes. Some pyroclastic currents even crossed the Bali Sea and reached the Gili Islands . This phase was probably phreatomagmatic , as the deposits show traces of water exposure.

Three pumice rains followed, some of which experienced maximum spread. Even on Sumbawa in the east they are seven centimeters thick.

The pumice was followed by other pyroclastic currents, probably triggered by the collapse of the eruption column and the rupture of the caldera. The streams reached a total volume of 29 cubic kilometers with thicknesses of up to 35 meters even at a distance of 25 kilometers from the outbreak focus. When they entered the sea in the north and east of Lombok, steam explosions occurred with the formation of pumice cones on the beach, while secondary pyroclastic currents formed.

The outbreak can thus be broken down into four phases:

  • Phreatic and first igneous phase P 1 - stable Plinian eruption column up to 40 kilometers in height
  • Phreatomagmatic phase with turbulent pyroclastic flows P 2 - significant water supply
  • Plinian phase P 3 - unstable eruption column, up to 43 kilometers altitude
  • Pyroclastic currents P 4 - low lava fountains, caldera collapse and collapse of the eruption column

Phases P 3 and P 4 should not have lasted more than twelve to 15 hours in total.

The tephra produced during the eruption fell on Java itself; it is classified here under the Muntilan Tephra . Their thickness in the Logung Lake was three centimeters. On the Agung in Bali twelve to 17 centimeters of tephra were deposited. The largest part had spread from the Samalas in a west to south-west direction. Samalas tephra was found even on the Merapi , 660 kilometers away, which allows a conclusion to be drawn about its total volume of 32 to 39 cubic kilometers. For the first phase, an area of ​​spread of 7500 square kilometers is assumed, for the third phase, however, 110,500 square kilometers, which implies a huge Plinian to Ultraplinian eruption.

The eruption column should have reached a height of 39 to 40 kilometers during phase P 1 with estimated wind speeds of ten meters / second and a record height of 38 to 43 kilometers during phase P 3. The height was in any case sufficient to prevent SO 2 from photolysis to undergo and affect the sulfur isotope ratio.

Different volume estimates are available for the eruption of the samala, depending on the author and the method used. Vidal and colleagues (2015) determined a minimum value of 8.3 cubic kilometers of DRE for the first three phases combined and 25 cubic kilometers of DRE alone for phase P 4. A total of at least 33 cubic kilometers of rock should therefore have been ejected. The outbreak temperature was around 1000 ° C. The chemical composition of the ejecta is trachydacite and contains the minerals amphibole , apatite , clinopyroxene , iron sulfide , orthopyroxene , plagioclase and titanomagnetite . The magma was created by fractionation from a previous basaltic melt.

The eruption with a volcanic explosion index of seven was one of the strongest in the Holocene after the eruption of Tambora in 1815 and was more powerful than the eruption of Krakatau in 1883. The Kuril Sea in the 7th millennium BC is roughly comparable . BC , Mount Mazama in the 6th millennium BC BC, the Tierra Bianca Joven on Lake Ilopango in the 6th millennium BC And the Minoan eruption in the 2nd millennium BC The fine-grained, cream-colored pumice horizons of the Samala form valuable tephrochronological correlation horizons on Bali . Samalas tephra was detected in ice cores even at a distance of 13,500 kilometers.

What was left behind was the “Segara Anak” caldera with an average diameter of six to seven kilometers. The height of the side walls varies between 700 and 2800 meters, the resulting crater lake is 200 meters deep. The volcanic cone of the Barujari rises 320 meters above sea level and has erupted fifteen times since 1847. A crater lake may already have existed before the eruption, which supplied the phreatomagmatic phase with 0.1 to 0.3 cubic kilometers of water. The water required could also come from aquifers. Rinjani, a little further to the east, was affected by the explosion, as it has a horseshoe-shaped collapse structure on the western edge .

The discovery of the eruption and the associated caldera was not made until 2003. A year later, the ejected volume was estimated at around 10 cubic kilometers. Early research dated the eruption between 1210 and 1300. In 2013, Lavigne and colleagues suggested moving the eruption to May to October 1257, as it triggered the climatic changes in the following year.

Research history

Infrared image of Lombok with the Samalas / Rinjani volcanic complex in the central northern part of the island

The existence of a significant volcanic eruption between 1257 and 1258 has been demonstrated by ice core data and medieval historical records in the Northern Hemisphere. Sulphate precipitation in polar ice caps suggested that the climatic fluctuations of this period were caused by a volcanic eruption. The global spread of precipitation indicated a tropical volcano , even if a volcano located near Greenland was initially considered. The strong rash in the sulphate concentrations was observed for the first time on the Greenland ice core Crête and was accompanied by a fine layer of rhyolite ash . Together with the rashes from 44 BC BC ( Etna ) and 426 BC It was the most significant change in the last 7000 years and was twice as strong as the Tambora signal from 1815.

In 2003, the ejected rock volume was estimated at 200 to 800 cubic kilometers, but at the same time it was admitted that the volume could have been significantly lower with increased sulphate content. Initially, the culprit could not be identified. At first the tofua was suggested, but it was then dropped because of its too weak breakout strength. The 1256 eruption of Harrat Rahat near Medina was also classified as too insignificant. The possibility of multiple simultaneous outbreaks was also considered. The estimates for the dimensions of the caldera were then between 10 and 30 kilometers.

In 2012, the Samalas or Rinjani volcano was seriously considered as an eruption focus for the first time. Other candidate candidates such as El Chichon and Quilotoa showed a different chemical composition in their “spikes” that did not match the sulfate content. These two volcanoes plus Okataina did not coincide with the event of 1257 either in time or in their explosiveness. In 2013 the so-called Babad Lombok were discovered in Indonesia . These are historical records written on palm leaves in Old Javanese in the 13th century . It was they who finally convinced Franck Lavigne that the samalas he had been watching for some time was indeed the source of the outbreak.

"All houses were destroyed, washed away or even floated on the sea and many people perished."

- Javanese text

The catastrophe occurred before the end of the 13th century. A geochemical analysis of glass fragments in ice cores was able to confirm their identity with the deposits on Lombok and thus blame the Samala eruption for the climatic effects.

Effects on the climate

The eruption of the Samala left sulfate maxima in ice cores in the northern and southern hemisphere, with the eruption in the southern hemisphere being the most pronounced in the last 1000 years and only surpassed in intensity by the eruption of the Laki crater in the northern hemisphere. Ice cores from Illimani in Bolivia also contain the sulfate spikes. The Pinatubo eruption in 1991, which released only a tenth of the sulfur of the Samalas eruption, should serve as a comparison for the intensity achieved . The sulfur deposits of the Samala could also be detected on Svalbard and the rain-down sulfuric acid may also have had a direct impact on peatlands in northern Sweden. The amount of SO 2 released is estimated at 158 ​​± 12 million tons. Compared to the Tambora eruption, this is significantly higher because the tephra was injected far better into the stratosphere and / or the sulfur content of the samalas magma was enriched.

Large volcanic eruptions transport aerosols into the atmosphere, which then form a haze in the stratosphere and thereby reduce solar radiation and then also global temperatures. Further consequences are problems in agriculture and possible famine. The social effects are usually less clear, as human societies are highly resilient . Not all cold summers are causally related to volcanic eruptions.

Observations at Pinatubo showed that the aerosol veil stayed for three years, so the sulphate precipitation at the poles from 1259 with the beginning of the eruption around 1257 corresponds to these three years.

Together with the eruption of the Kuwae around 1450 and Tambora in 1815, the eruption of the Samala represents one of the most significant cooling of the last millennium. In drill cores from the Urals , its deposits form the clearest volcanic signal. The winter of 1257/1258 set in early but was relatively warm, suggesting reports from France of the early blooming of violets . The phenomenon of a warm winter after major volcanic explosions is supported by many observations. However, the following summer was very cold and the following winter was long and cold. The cooling in the summer of 1258 was 0.69 ° K in the southern hemisphere and 0.46 ° K in the northern hemisphere. In comparison, the reduction in radiation from the Pinatubo eruption in 1991 was only one seventh of these values. The surface temperatures of the world's oceans also fell by 0.3 to 2.2 ° C and triggered changes in the circulation pattern and the formation of deep water . The temperature drops may have lasted for a decade. At the same time, precipitation and evaporation were reduced, with evaporation being more severely affected.

Dendrochronological records of the Samalas eruption are incomplete. Climate model calculations show a global cooling of up to 2 ° C, a very high amount that the proxy data does not follow. Improved models show an anomaly for the year 1258, which dragged on to 1261. However, some climate models overestimate the climatic effects because they assume a linear relationship between the optical aerosol effectiveness and the amount of sulfur emitted. An El Nino event shortly before the eruption may have further weakened the cooling effect.

The eruption of the Samala in conjunction with another eruption in the 14th century led to an increase in the ice caps and sea ​​ice , and in Norway the glaciers even advanced. Possibly it also influenced the North Atlantic Oscillation , which assumed significantly more negative values ​​in the following decades. In addition, solar activity was also declining ( wolf minimum ). The ice advances presumably contributed to an intensification and prolongation of the climatic effects. Further volcanic events in 1269, 1278 and 1286 intensified the expansion of the ice cover. The glacier advances are documented on Baffin Island , as here the glaciers trapped vegetation in the ice when they advanced. In Arctic Canada , the transition from a warm to a colder climatic phase also coincides with the Samala eruption.

The eruption of the Samala occurred at a time when the Medieval Warm Period - a period of climatic stability - was coming to an end. Previous eruptions in 1108, 1171 and 1230 had already contributed to the destabilization of this epoch. The period from 1250 to 1300 is then characterized by generally increased volcanism - documented by a moraine advance on Disko Island ( Greenland ), which can also be explained by a cold snap that set in before the Samalas eruption. Overall, it is quite possible that all these volcanic climatic inputs, coupled with increased ice cover, initiated the Little Ice Age , without having to resort to changed solar radiation parameters. But this theory is controversial.

Traces of the outbreak can be found in Mongolia between 1258 and 1262, among other things on the basis of reduced annual rings on trees. In Vietnam fell monsoon very wet out. However, other regions such as Alaska were largely spared climatic changes, presumably because of the climatic moderation by the Pacific. Also Scandinavia , Quebec and the western United States have only a slight deterioration in their annual rings.

Social impact

The social effects of the Samalas eruption are likely to have been catastrophic in parts at the end of 1257 and 1258. In Babad Lombok it is described that entire villages were destroyed in the middle of the 13th century by ash rains and rock-laden gas turbulence that spread at high speed. According to a Javanese inscription, the kingdom on Lombok, including its capital Pamatan, was completely destroyed by the eruption, only the royal family survived. Thousands and thousands of people perished in the inferno and it is possible that Lombok and Bali were completely depopulated, which allowed Kertanegra to conquer Bali in 1284 without major resistance.

Reports from France and England in 1258 indicate that the land was covered by a dry fog, which local observers saw as permanent cloud cover. Medieval records from 1258 tell of a cold and rainy summer with floods and poor harvests. In particular, the months February to June were extremely cold. In the years 1258 and 1259, changes in color tones were observed in the atmosphere not only in Europe, but also in the Middle East. Added to this were stormy, cold and severe weather conditions. The rainy weather damaged crops, which in turn led to famine and epidemics. North-western Europe seems to have been badly affected and so crop failures and a famine in London can be correlated with the outbreak of Samala. In London, 15,000 to 20,000 people died of famine at the time. Matthäus Paris reports from Saint Albans that the weather alternated between cold and heavy rain until the middle of August, thus driving up the mortality rate:

"Bloated and rotting, the dead lay in groups of five or six in pigsties, on dung heaps or in muddy streets."

- Matthew Paris, chronicler of Saint Albans

The resulting famine was so severe that grain had to be imported from Germany and Holland . Grain prices soared in Great Britain, but also in France and Italy. Epidemics are reported from England and the Middle East at this time . But serious problems also arose in China, Japan and Korea . Less extreme weather conditions are recorded after the winter of 1258/1259, but the winter of 1260/1261 was again very severe in Iceland , Italy and elsewhere.

A possible long-term consequence of the outbreak was the gradual loss of control of Byzantium over Western Anatolia, which was based on the replacement of Byzantine peasants by Turkish shepherds. The origins of the flagellants can possibly also be traced back to the social effects of the outbreak, whereby armed conflicts and other misery are by no means to be neglected.

Movies

  • Mysterious volcanic eruption . Documentation, Arte France 2017. Director: Pascal Guérin.

Individual evidence

  1. ^ Reid, Anthony: Revisiting Southeast Asian History with Geology: Some Demographic Consequences of a Dangerous Environment . Ed .: Bankoff, Greg and Christensen, Joseph. Natural Hazards and Peoples in the Indian Ocean World. Palgrave Macmillan US, 2016, ISBN 978-1-349-94857-4 , pp. 33 , doi : 10.1057 / 978-1-349-94857-4_2 .
  2. ^ Sigl, M. et al.: Insights from Antarctica on volcanic forcing during the Common Era . In: Nat. Clim. Change . tape 4 , 2014, p. 693-697 .
  3. ^ Simons, WJF et al.: A decade of GPS in Southeast Asia: resolving Sundaland motion and boundaries . In: Journal of Geophysical Research . B06420, 2007, doi : 10.1029 / 2005JB003868 .
  4. ↑ Mangga, SA, Atmawinata, S., Hermanto, B. and Setyogroho, B .: Geological Map of The Lombok Sheet, West Nusa Tenggara, scale 1: 250,000 . Geological Research and Development Center, Bandung 1994.
  5. ↑ a b Nasution, A., Takada, A. and Rosgandika, M .: The volcanic activity of Rinjani, Lombok Island, Indonesia, during the last thousand years, viewed from 14C datings; Abstract . In: The 33rd Annual Convention & Exhibition, IAGI, 29 Nov-1 Oct 2004 . Bandung, Indonesia 2004.
  6. ↑ F. Lavigne, J.-P. Degeai, J.-C. Komorowski, S. Guillet, V. Robert, P. Lahitte, C. Oppenheimer, M. Stoffel, CM Vidal, Surono, I. Pratomo, P. Wassmer, I. Hajdas, DS Hadmoko, E. de Belizal: Source of the great AD 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia . In: Proceedings of the National Academy of Sciences . tape 110 , no. 42 , October 15, 2013, p. 16742-16747 , doi : 10.1073 / pnas.1307520110 .
  7. ↑ a b Rachmat, Heryadi, Rosana, Mega Fatimah, Wirakusumah, Ade Djumarma and Jabbar, Gamma Abdul: Petrogenesis of Rinjani Post-1257-Caldera-Forming-Eruption Lava Flows . In: Indonesian Journal on Geoscience . tape 3 (2) , 2016, doi : 10.17014 / ijog.3.2.107-126 .
  8. ↑ Komorowski, J., Metrich, N. and Vidal, C .: Final Research Report for Ristek - 2013 . Institute de Physique Du Globe de Paris 2014.
  9. ↑ Abbott, MJ and Chamalaun, FH: Geochronology of some Banda Arc volcanics . In: The geology and tectonics of Eastern Indonesia . tape 2 , 1981, p. 253-268 .
  10. ^ Foden, JD and Varne, R .: The Geochemistry and Petrology of Basalt-Andesite-Dacite Suite from Rinjani Volcano, Lombok: Implications for The Petrogenesis of Island Arc, Calcalkaline Magmas . In: The Geology and Tectonics of Eastem Indonesia, Geological Research and Development Center . Special Publication, 2, 1981, pp. 115-134 .
  11. ↑ Curray, JR, Shor, Jr., GG, Raiit, RW and Henry, M .: Seismic refraction and reflection studies of crustal structure of the eastern Sunda and western Banda arcs . In: Journal of Geophysical Research . tape 82 , 1977, pp. 24792489 , doi : 10.1029 / JB082i017p02479 .
  12. ^ Nasution, A., Takada, A., Udibowo, Widarto, D. and Hutasoit, L .: Rinjani and Propok Volcanics as a Heat Sources of Geothermal Prospect from Eastern Lombok, Indonesia . In: Jurnal Geoaplika . tape 5 (1) , 2010, p. 001-009 .
  13. ↑ Nakagawa, M., Takahashi, R., Amma-Miyasaka, M., Kuritani, T., Wibowo, H., Furukawa, R. and Takada, A .: Petrology of Rinjani volcano, Indonesia: The magmatic processes before and during AD 1257 calderaforming eruption . In: Japan Geoscience Union Meeting; 2015 May 24-28th: ​​Makuhari Messe . Chiba 2015.
  14. ↑ Crowley, TJ and Unterman, MB: Technical details concerning the development of a 1200 yr proxy index for global volcanism . In: Earth System Science Data . tape 5 (1) , 2013, pp. 193 , doi : 10.5194 / essd-5-187-2013 .
  15. ↑ a b c Vidal, Céline M. et al .: Dynamics of the major plinian eruption of Samalas in 1257 AD (Lombok, Indonesia) . In: Bulletin of Volcanology . tape 77 (9) , 2015, pp. 73 , doi : 10.1007 / s00445-015-0960-9 .
  16. ↑ Vidal, Celine M., Métrich, Nicole, Komorowski, Jean-Christophe, Pratomo, Indyo, Michel, Agnès, Kartadinata, Nugraha, Robert, Vincent and Lavigne, Franck: The 1257 Samalas eruption (Lombok, Indonesia): the single greatest stratospheric gas release of the Common Era . In: Scientific Reports . tape 6: 34868 , 2016, doi : 10.1038 / srep34868 .
  17. Jump up ↑ Timmreck, Claudia, Lorenz, Stephan J., Crowley, Thomas J., Kinne, Stefan, Raddatz, Thomas J., Thomas, Manu A. and Jungclaus, Johann H .: Limited temperature response to the very large AD 1258 volcanic eruption . In: Geophysical Research Letters . 36 (21): L21708, 2009, doi : 10.1029 / 2009GL040083 .