Ata Caldera

{{short description|Mostly-submerged caldera in Kagoshima Prefecture, Japan}} {{Infobox mountain  | name= Ata Caldera | native_name={{native name|ja|阿多カルデラ}} | other_name=  | etymology=   | image_size=  | country= Japan | subdivision1= Kagoshima Prefecture | subdivision2_type= Region | subdivision2= Ibusuki, Kagoshima, Kimotsuki District, Tarumizu | subdivision4_type = Geological Subdivisions | subdivision4 = Ata South Caldera, Ata North Caldera, Ikeda Caldera | coordinates= {{coord|31.40|N|130.64|E|type:mountain_region:IT_scale:100000|format=dms|display=inline,title}} | coordinates_ref=<ref name="GVPata">{{Cite web|url=https://volcano.si.edu/volcano.cfm?vn=282070|title=Ata {{!}}Global Volcanism Program {{!}} Smithsonian Institution|website=volcano.si.edu|language=en|access-date=2022-09-19}}</ref>  | highest=Mount Kaimon | highest_location={{coord|31|10|48|N|130|31|42|E|type:mountain_scale:100000|format=dms|display=inline}} | elevation_m=924  | length_km= 25 | length_orientation= NS | width_km= 15 | width_orientation= EW | area_km2=  | geology= | orogeny= | age= Pleistocene (240,000 years ago) onwards | type=Caldera<br/>Somma volcano | last_eruption= 885 CE<ref name="GVPata" />  | map_caption= | map = Japan | location = Kagoshima, Japan | image_map= {{OSM Location map | coord = {{coord|31.4|130.8}}  | zoom = 8  | float =center | height = 500 | width = 260 | map-raw={{Wikipedia:Map data/Kagoshima graben}} | arcA = "Ōsumi islands",30.6,130.2,12px, #777755, 10deg, 1.5, 0.75, 1 | arcB = "Inner and Outer",30.82,130.37,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcC = "Kikai Caldera",30.77,130.57,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcD = "Ata South Caldera",31.15,130.85,12px, #ff0000, 0deg, 0.09, 7.5, 1 | arcE = "Ata North Caldera",31.29,130.85,12px, #ff0000, 0deg, 0.09, 7.5, 1 | arcF = "Aria Caldera",31.54,130.87,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcG = "Kakuto",32.1,130.47,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcH = "Caldera",31.99,130.47,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcI = "Kobayashi",32.035,131.01,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | arcJ = "Caldera",31.93,131.04,12px, #ff00ff, 0deg, 0.09, 7.5, 1 | title = | caption = Map showing the Ata calderas {{legend-line|red solid 2px|(red)|inline=yes}} within the Kagoshima graben {{legend-line|#000000 solid 2px|(black) |inline=yes}} with the other graben caldera {{legend-line|violet solid 2px|(violet)|inline=yes}} and active volcanoes as symbols<ref name="Nishihara2022"/> }} }}

{{nihongo|'''Ata Caldera'''|阿多カルデラ|Ata karudera}}, containing the Ata North Caldera (AtaN Caldera),<ref name="Nishihara2022">{{cite journal|last1=Nishihara |first1=A. |last2=Geshi |first2=N. |last3=Naruo |first3= H. |year= 2022 |title= Long-term change of the eruption activities of Sakurajima volcano, Japan, inferred from the fallout tephra deposits|journal=Frontiers in Earth Science|volume=10 |at=988373 |doi=10.3389/feart.2022.988373 |bibcode=2022FrEaS..10.8373N |doi-access=free }}</ref> and the Ata South Caldera (AtaS Caldera),<ref name="Nishihara2022"/> which in turn contains Mount Kaimon and Ikeda Caldera amongst other volcanoes, is a massive, ill defined, mostly submerged volcanic caldera structure associated with the southern portions of Kagoshima Bay.

==Geology== The earliest tephra assigned to the volcano, is the widespread on regional sea bed cores, Ata–Torihama tephra (Ata-Th) at 240,000 years before the present.<ref name="Ikehara2015">{{cite journal|last1=Ikehara |first1=Ken |title=Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology |year=2015|journal=Progress in Earth and Planetary Science |volume=2 |issue=36 |pages=1–12 |doi=10.1186/s40645-015-0068-z|bibcode=2015PEPS....2...36I |s2cid=45727649 |url=https://progearthplanetsci.springeropen.com/counter/pdf/10.1186/s40645-015-0068-z.pdf |doi-access=free }}</ref>

The caldera contributed to an eruption which has been dated to about 100,000 years before present (range by various techniques mostly fall 100,000 to 109,000) that generated the Ata tephra in southern Japan.<ref name="Okuno2019">{{cite journal|first1=Mitsuru |last1=Okuno|title= Chronological study on widespread tephra and volcanic stratigraphy of the past 100,000 years |journal= The Journal of the Geological Society of Japan |volume=125 |issue=1 |pages=41–53 |date=2019-04-15 |issn=1349-9963 |doi=10.5575/geosoc.2018.0069 |s2cid=146526393 |url=https://www.jstage.jst.go.jp/article/geosoc/125/1/125_2018.0069/_article/-char/en |doi-access=free }}</ref> This eruption has been assigned a VEI of 7.5 and generated over {{convert|300|km3|abbr=on}} of tephra.<ref name="Smith2013">{{cite journal|first1=Victoria C. |last1=Smith|first2= Richard A. |last2=Staff|first3= Simon P.E. |last3=Blockley|first4= Christopher Bronk |last4=Ramsey|first5= Takeshi |last5=Nakagawa|first6= Darren F. |last6=Mark|first7= Keiji |last7=Takemura|first8= Toru |last8=Danhara |title=Identification and correlation of visible tephras in the Lake Suigetsu SG06 sedimentary archive, Japan: chronostratigraphic markers for synchronising of east Asian/west Pacific palaeoclimatic records across the last 150 ka |journal= Quaternary Science Reviews |volume=67|year=2013 | pages=121–137 |issn=0277-3791 |doi=10.1016/j.quascirev.2013.01.026 |bibcode=2013QSRv...67..121S |url=https://www.sciencedirect.com/science/article/pii/S0277379113000413 |url-access=subscription }}</ref> This is overlaid in some places in Japan by the more recent Mitake No. 1 (On-Pm1) tephra from an eruption in the Mount Ontake area and K-Tz tephra from the Kikai Caldera.<ref name="Okuno2019"/> There have been many more lesser eruptions.

===Structure=== Increasingly the recent literature separates the caldera into a northern almost completely submerged caldera that generated the Ata tephra and Ata ignimbrite, and a southern caldera which includes the recently active Ikeda Caldera and the Kaimondake stratovolcano in the Ibusuki Volcanic Field.<ref name="IAVCEI2013">{{cite web|access-date=2022-09-19|title=IAVCEI 2013 Scientific Assembly A Guide for Mid-Conference Field Trip |url=https://fdocuments.in/document/2014-1-21-kirishima-sakurajima-and-kaimondake-on-kyushu-and-several-volcanic.html?page=1 }}</ref><ref name="Nishihara2022"/> The southern caldera first had the Ata name but is not believed now to be associated with the vents of the major eruption of 100,000 years ago.<ref name="Matumoto1965">{{cite journal|access-date=2022-09-19|last1=Matumoto |first1=Tadaiti|title=Calderas of Kyusyu|url=https://www.oregongeology.org/pubs/ofr/O-66-01.pdf|date=1965-08-28|journal=Transactions of the Luna Geological Field Conference}}</ref> High resolution Bouguer gravity imaging of Kyushu is consistent with the larger caldera being the Ata North Caldera but suggests it may be centered near the island of Chiringashima, and that the Ata South Caldera is the smaller in size, overlaps it being centred near Yamagawafukumoto district.<ref name="Shichi2005">{{cite book|last1=Shichi |first1= R. |last2=Yamamoto |first2= A. |last3= Kudo |first3= T. |last4= Murata |first4= Y. |last5=Nawa |first5= Kazunari |last6= Komazawa |first6= Masao |last7= Nakada |first7= M. |last8=Miyamachi |first8= H. |last9=Komuro |first9= Hitoshi |last10= Fukuda|first10= Yoichi |last11= Higashi |first11= T. |last12= Yusa |first12= Y.|title= A Window on the Future of Geodesy |chapter= A Gravity Database of Southwest Japan: Application to Bouguer Gravity Imaging in Kyushu District, Southwest Japan |series= International Association of Geodesy Symposia |year=2005 |volume= 128 |doi= 10.1007/3-540-27432-4_40 |url=https://www.researchgate.net/publication/251134851 |pages=236–241 |isbn= 3-540-24055-1 }}</ref>

The National Catalogue of the Active Volcanoes of Japan (JMA, 2013) included features of the Ibusuki Volcanic Field as part of the Ata post-caldera system.<ref name="GVPata" /> By this definition the single caldera may be a rounded triangle about {{cvt|30|km}} in length and up to {{cvt|25|km}} in width,<ref name="IAVCEI2013"/> although the usual quoted size is smaller.

===Relationships=== Immediately adjacent to the north of the caldera is the Sakurajima volcano in Aira Caldera and further away to the south along what has been termed the Kagoshima graben<ref name="IAVCEI2013"/> is the Kikai Caldera.<ref name="Geshi2020">{{cite journal|last1=Geshi |first1= N. |last2=Yamada |first2= I. |last3= Matsumoto |first3= K. |last4= Nishihara |first4=A. |last5= Miyagi |first5=I. |title= Accumulation of rhyolite magma and triggers for a caldera-forming eruption of the Aira Caldera, Japan |journal= Bulletin of Volcanology |volume=82 |issue= 44 |year=2020 |page= 44 |doi=10.1007/s00445-020-01384-6|bibcode= 2020BVol...82...44G |s2cid= 218652170 |url=https://link.springer.com/article/10.1007/s00445-020-01384-6 |url-access= subscription }}</ref> This alignment was first described by Tadaiti Matumoto in the 1940s.<ref name="Matumoto1965"/> The alignment extends all the way north past Mount Kirishima to intersect the Aso Caldera by gravitational anomaly.<ref name="Shichi2005"/> The tectonic processes are rather complex in this region involving the larger Philippine Sea plate and Eurasian plate where the smaller Okinawa plate is colliding with the Amur plate and the larger Pacific plate is subducting under both.

==References== {{Reflist}}

Category:VEI-7 volcanoes Category:Calderas of Kyushu Category:Submarine calderas Category:Pleistocene calderas Category:Active volcanoes Category:Volcanoes of Kagoshima Prefecture Category:Paleolithic Japan

Ata Caldera

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