Editing Mount Tambora (section)

=== Geological history ===
==== Formation ====
[[File:Plate setting Sunda megathrust.png|thumb|upright=1.2|Plate boundaries of Indonesia, with the location of Mount Tambora to the lower right of "11"]]
Tambora lies 
{{convert|340|km|mi}} north of the [[Java Trench]] system and {{convert|180|to|190|km|mi}} above the upper surface of the active north-dipping [[subduction zone]]. Sumbawa Island is flanked to the north and south by [[oceanic crust]].<ref name="Foden1980">{{cite journal |title=The petrology and tectonic setting of Quaternary—Recent volcanic centres of Lombok and Sumbawa, Sunda arc |journal=Chemical Geology |last1=Foden |first1=J. |last2=Varne |first2=R. |volume=30 |issue=3 |date=1980 |pages=201–206 |doi=10.1016/0009-2541(80)90106-0 |bibcode=1980ChGeo..30..201F}}</ref> The convergence rate of the [[Australian Plate]] beneath the [[Sunda Plate]] is {{convert|7.8|cm|in}} per year.<ref name="Sigurdsson1989">{{cite journal |date=1989 |title=Plinian and co-ignimbrite tephra fall from the 1815 eruption of Tambora volcano |journal=Bulletin of Volcanology |last1=Sigurdsson |first1=H. |last2=Carey |first2=S. |volume=51 |issue=4 |pages=243–270 |doi=10.1007/BF01073515 |bibcode=1989BVol...51..243S |s2cid=132160294}}</ref> Estimates for the onset of the volcanism at Mount Tambora range from 57<ref name="Degens1989"/> to 43 [[kiloannum|ka]]. The latter estimate published in 2012 is based on argon dating of the first pre-caldera lava flows.<ref name="Gertisser"/> 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.<ref name="Degens1989"/>

A high volcanic cone with a single central vent formed before the 1815 eruption, which follows a [[stratovolcano]] shape.<ref name="VSI">{{cite web |title=Geology of Tambora Volcano |publisher=Vulcanological Survey of Indonesia |url=http://www.vsi.esdm.go.id/volcanoes/tambora/geology.html |url-status=dead |archive-url=https://web.archive.org/web/20071024202358/http://www.vsi.esdm.go.id/volcanoes/tambora/geology.html |archive-date=24 October 2007 |access-date=2 August 2018}}</ref> The diameter at the base is {{convert|60|km|mi}}.<ref name="Foden1986"/> The volcano frequently erupted lava, which descended over steep slopes.<ref name="VSI" /> Tambora has produced [[trachybasalt]] and [[trachyandesite]] rocks which are rich in [[potassium]]. The volcanics contain [[phenocryst]]s of [[apatite]], [[biotite]], [[clinopyroxene]], [[leucite]], [[magnetite]], [[olivine]] and [[plagioclase]], with the exact composition of the phenocrysts varying between different rock types.<ref name="Foden1986"/> [[Orthopyroxene]] is absent in the trachyandesites of Tambora.<ref name=Foden1979_p49>Foden, 1979, p. 49</ref> Olivine is most present in the rocks with less than 53 percent SiO<sub>2</sub>, while it is absent in the more silica-rich volcanics, characterised by the presence of biotite phenocrysts.<ref name=Foden1979_p50>Foden, 1979, p. 50</ref> The mafic series also contain [[titanium]] [[magnetite]] and the trachybasalts are dominated by [[anorthosite]]-rich plagioclase.<ref name=Foden1979_p51>Foden, 1979, p. 51</ref> [[Rubidium]], [[strontium]] and [[phosphorus pentoxide]] are especially rich in the lavas from Tambora, more than the comparable ones from [[Mount Rinjani]].<ref name=Foden1979_p56>Foden, 1979, p. 56</ref> The lavas of Tambora are slightly enriched in [[zircon]] compared with those of Rinjani.<ref name=Foden1979_p60>Foden, 1979, p.60</ref>

The [[magma]] involved in the 1815 eruption originated in the [[mantle (geology)|mantle]] and was further modified by melts derived from [[subduct]]ed sediments, fluids derived from the subducted crust and crystallization processes in [[magma chamber]]s.<ref name="Gertisser">{{cite journal |date=1 February 2012 |last1=Gertisser |first1=R. |last2=Self |first2=S. |last3=Thomas |first3=L.E. |last4=Handley |first4=H.K. |last5=Van Calsteren |first5=P. |last6=Wolff |first6=J.A. |title=Processes and Timescales of Magma Genesis and Differentiation Leading to the Great Tambora Eruption in 1815 |journal=Journal of Petrology |volume=53 |issue=2 |pages=271–297 |doi=10.1093/petrology/egr062 |bibcode=2012JPet...53..271G |doi-access=free}}</ref> <sup>87</sup>Sr<sup>86</sup>Sr ratios of Mount Tambora are similar to those of Mount Rinjani, but lower than those measured at Sangeang Api.<ref name="Foden1980"/> [[Potassium]] levels of Tambora volcanics exceed 3 weight percent, placing them in the [[shoshonite]] range for alkaline series.<ref name="Fiorentini2010">{{cite journal |year=2010 |last1=Fiorentini |first1=Marco L. |last2=Garwin |first2=Steve L. |title=Evidence of a mantle contribution in the genesis of magmatic rocks from the Neogene Batu Hijau district in the Sunda Arc, South Western Sumbawa, Indonesia |journal=Contributions to Mineralogy and Petrology |volume=159 |issue=6 |page=826 |doi=10.1007/s00410-009-0457-7 |bibcode=2010CoMP..159..819F |s2cid=129804058}}</ref>

Since the 1815 eruption, the lowermost portion contains deposits of interlayered sequences of [[lava]] and [[Pyroclastic rock|pyroclastic]] materials. Approximately 40% of the layers are represented in the {{cvt|1|to|4|m|ft|adj=mid|-thick}} lava flows.<ref name="VSI"/> Thick [[scoria]] beds were produced by the fragmentation of lava flows. Within the upper section, the lava is interbedded with scoria, [[tuff]]s, [[pyroclastic flow]]s and [[pyroclastic fall]]s.<ref name="VSI"/> Tambora has at least 20 [[parasitic cone]]s<ref name="Sigurdsson1989"/> and [[lava dome]]s, including ''Doro Afi Toi'', ''Kadiendi Nae'', ''Molo'' and ''Tahe''.<ref name="SynonymsSubfeatures">{{cite gvp |name=Tambora: Synonyms & Subfeatures |vtab=Subfeatures |vn=264040 |access-date=2021-06-24}}</ref> The main product of these parasitic vents is [[basaltic]] [[lava flow]]s.<ref name="Sigurdsson1989"/>

==== Eruptive history ====
[[Radiocarbon dating]] has established that Mount Tambora had erupted three times during the current [[Holocene]] [[Epoch (geology)|epoch]] before the 1815 eruption, but the magnitudes of these eruptions are unknown. Their estimated dates are 3910&nbsp;BC ± 200 years, 3050&nbsp;BC and 740&nbsp;AD ± 150 years.<ref name="EruptiveHistory">{{cite gvp |name=Tambora: Eruptive History |vtab=Eruptions |vn=264040 |access-date=2021-06-24}}</ref> 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.<ref name="Gertisser"/>

In 1812, Mount Tambora became highly active, with its maximum eruptive intensity occurring in April 1815.<ref name="EruptiveHistory"/> The magnitude was 7 on the [[Volcanic Explosivity Index]] (VEI) scale, with a total [[tephra]] ejecta volume of up to 1.8&nbsp;×&nbsp;10<sup>11</sup>&nbsp;cubic metres.<ref name="EruptiveHistory"/> Its eruptive characteristics included central vent and explosive eruptions, pyroclastic flows, [[tsunami]]s and caldera collapse. This eruption had an effect on global climate. Volcanic activity ceased on 15 July 1815.<ref name="EruptiveHistory"/> Activity resumed in August 1819—a small eruption with "flames" and rumbling [[aftershock]]s, and was considered to be part of the 1815 eruption.<ref name="Oppenheimer2003"/> This eruption was recorded at 2 on the VEI scale.

Around 1880&nbsp;±&nbsp;30 years, eruptions at Mount Tambora have been registered only inside the caldera.<ref name="EruptiveHistory"/> It created small lava flows and lava dome [[Extrusive (geology)|extrusions]]; this was recorded at two on the VEI scale. This eruption created the ''Doro Api Toi'' parasitic cone inside the caldera.<ref>{{cite web |title=Tambora Historic Eruptions and Recent Activities |publisher=Vulcanological Survey of Indonesia |url=http://www.vsi.esdm.go.id/volcanoes/tambora/history.html |archive-url=https://web.archive.org/web/20070927043444/http://www.vsi.esdm.go.id/volcanoes/tambora/history.html |url-status=dead |archive-date=27 September 2007 |access-date=2 August 2018}}</ref>

Mount Tambora is still [[active volcano|active]] and minor lava domes and flows were extruded on the caldera floor during the 19th and 20th centuries.<ref name="gvp"/> The last eruption was recorded in 1967. It was a gentle eruption with a VEI of 0, which means it was non-explosive.<ref name="EruptiveHistory"/><ref>{{cite web |title=Volcanic Explosivity Index (VEI) |url=http://www.volcano.si.edu/world/eruptioncriteria.cfm#VEI |work=Global Volcanism Program |publisher=[[Smithsonian Institution|Smithsonian National Museum of Natural History]] |archive-url=https://web.archive.org/web/20111110173623/http://www.volcano.si.edu/world/eruptioncriteria.cfm |archive-date=10 November 2011 |access-date=2 August 2018}}</ref> Another very small eruption was reported in 2011.<ref>{{cite book |last=Wood |first=Gillen D'Arcy |title=Tambora: The Eruption That Changed the World |publisher=Princeton University Press |date=2014 |pages=1–312 |isbn=9780691168623}}</ref> 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.<ref>{{cite web |url=http://portal.vsi.esdm.go.id/index.php?option=com_content&view=article&id=203%3Apeningkatan-status-g-tambora-dari-normal-ke-waspada&catid=35%3Aaktifitas-terkini-gai |title=Peningkatan Status G. Tambora dari Normal ke Waspada |publisher=Directorate of Volcanology and Geological Hazard Mitigation, Indonesia |date=30 August 2011 |archive-url=https://web.archive.org/web/20110908003204/http://portal.vsi.esdm.go.id/index.php?option=com_content&view=article&id=203%3Apeningkatan-status-g-tambora-dari-normal-ke-waspada&catid=35%3Aaktifitas-terkini-gai |archive-date=8 September 2011 |language=id |access-date=2 August 2018}}</ref><ref>{{cite journal |last1=Wunderman |first1=Richard |title=Report on Tambora (Indonesia) |journal=Bulletin of the Global Volcanism Network |date=2011 |volume=36 |issue=8 |doi=10.5479/si.GVP.BGVN201108-264040}}</ref>