Editing Kikai Caldera (section)

== 2024 studies ==
Japanese scientists conducted an extensive study of the volcanic activity of the Kikai underwater caldera. They had estimated the volumes of ejected volcanic material, which range from 332 to 457 cubic kilometers, and proved that it was the largest eruption in the last 11,700 years that occurred here 7,300 years ago. They were able to recreate the sequence of a large-scale volcanic event and identified three directions of flow of eruption products: in the atmosphere, along the seabed and along the water's edge.

Details of the marine expedition include conducting seismological studies and collecting sediment samples around the Kikai caldera. Scientists have confirmed that volcanic formations on the ocean floor and nearby islands have a common position. Analysis of the distribution of these deposits around the eruption site helps to understand how the pyroclastic flow and water interacted. The eruption occurred with a strong ejection of debris and ash, which corresponds to the usual phase of the Plinian type, during which there was a series of prolonged emissions under high pressure of fragmented lava and pumice in the form of a gas-ash mixture. It was a volumetric pyroclastic flow as a final stage, which partially spread along the seabed and released into the atmosphere in the form of an eruptive column (ash, fragments of pumice, small crystals and tephra). The tephra cloud covered an area of more than 2.8 million km2. The volume of ash material amounted to more than 370 km3 in terms of hard rock. The Plinian phase ended with the destruction of the eruptive column. A huge column of hot tephra fell a few hundred meters from the eruption’s center, causing the formation of a pyroclastic flow.

Since the center of the volcano was under water, the Akahoya eruption had the character of a steam explosion (or a series of explosions) due to the instantaneous release of steam upon contact of hot magma with water. As a result, a double caldera was formed.

Scientists had conducted a detailed study of the spread of volcanic material over an area of about 4,500 square kilometers around the center of the eruption and mapped the thickness of the underwater pyroclastic sediment. In their opinion, 133 to 183 cubic kilometers of pumice and ash settled on the studied area.

After analyzing the textures and nature of the fragments of the underwater volcanic strata, the authors concluded that it was formed from a suspended stream, which can cover long distances even up the slope, as it turned out. Having built a model of the Kikai-Akahoya eruption, researchers have found that in addition to the underwater pyroclastic flow and the powerful release of the tephra cloud into the atmosphere, there was also a third stream of thin volcanic material that spread along the surface of the water to the nearest islands.<ref>{{cite web |title=Кальдера Кикай у берегов Японии — место крупнейшего в голоцене извержения вулкана |url=https://elementy.ru/novosti_nauki/434220/Kaldera_Kikay_u_beregov_Yaponii_mesto_krupneyshego_v_golotsene_izverzheniya_vulkana |accessdate=2024-05-22 |publisher=elementy.ru |language=ru}}</ref>

===Eruptive history since Kikai-Akahoya eruption===
Kikai is still an active volcano. [[Mount Iō (Iōjima)|Io-dake (Mount Iō)]], Inamura-dake (south coast of [[Iōjima (Kagoshima)|Satsuma-Io-jima]]), Tokara-Iwo-Jima (north east coast of Satsuma-Io-jima) and [[Shōwa Iōjima]] (Shin-Io-jima) are post-caldera volcanoes within it.<ref name="gbank"/>  Minor eruptions occur frequently on Mount Iō, one of the post-caldera [[subaerial]] volcanic peaks on Iōjima. Iōjima is one of three volcanic islands, two of which lie on the caldera rim.  On June 4, 2013, weak tremors were recorded. Shortly after, eruptions began and continued off-and-on for several hours.<ref name=GVP /> Io-dake is monitored for earthquake, gas and steam plume activity so that between the 2020 and 2023 eruptions it is known to have had continuous low grade activity.<ref name=GVP />

[[file:2015 Satsuma-Iojima Iodake.jpg|thumb|250px|[[Mount Iō (Iōjima)|Mount Iō]], a [[rhyolite]] [[lava dome]], May, 2015, viewed from the east]]
Eruptions occurred:<ref name="gbank"/><ref name="Maeno2005">{{cite journal|last1=Maeno |first1=Fukashi |last2=Taniguchi |first2= Hiromitsu |date=2005-05-20 |pages= 71–85|title=Eruptive History of Satsuma Iwo-jima Island, Kikai Caldera, after a 6.5 ka Caldera-forming Eruption |doi=10.18940/kazan.50.2_71|journal=火山 (Volcano)|volume=50 |url=https://www.jstage.jst.go.jp/article/kazan/50/2/50_KJ00003562590/_article/-char/ja/}}</ref>
*old Iwo-dake stage (stage OIo-I-II)
**phreatomagmatic eruptions and pumice fallout (stage OIo-I), followed by rhyolitic lava with continuous [[tephra]], resulting in a volcanic edifice (stage OIo-II)
**3250 BCE ± 75 years (uncalibrated) Old Iwo-dake
***OIo1a,b tephras<ref name="GVP"/>
**2450 BCE ± 840 years ([[tephrochronology]]) Old Iwo-dake
***OIo2a,b tephras<ref name="GVP"/>
* Inamura-dake stage (stage In-I-IV)
**basaltic lava flows and scoria-cone building (stage In-I-II), then phreatomagmatic eruptions (stage In-III), and then andesitic lava (stage In-IV)
**1830 BCE ± 75 years (uncalibrated) Inamura-dake<ref name="GVP"/>
***In-I tephra
**1090 BCE ± 100 years (uncalibrated) Inamura-dake<ref name="GVP"/>
*young Iwo-dake stage (stage YIo-I-IV)
**continuing with a different magma source including rhyolitic lava and intermittent pumice
**280 BCE ± 75 years (uncalibrated) Iwo-dake<ref name="GVP"/>
**390 ± 100 years (uncalibrated) Iwo-dake<ref name="GVP"/>
**750 (tephrochronology) Iwo-dake<ref name="GVP"/>
**830 ± 40 years (uncalibrated) Iwo-dake<ref name="GVP"/>
***K-Iw-P1 tephra
**1010 ± 40 years (uncalibrated) Iwo-dake<ref name="GVP"/>
*** K-Sk-u-3 tephra
**1030 ± 40 years (uncalibrated) Iwo-dake<ref name="GVP"/>
***K-Sk-u-4 tephra
**1340 ± 30 years (uncalibrated) Iwo-dake<ref name="GVP"/>
***K-Iw-P2 tephra
**1430 ± 75 years (uncalibrated) Iwo-dake<ref name="GVP"/>
** 13 Feb 1914 Tokara-Iwo-Jima<ref name="GVP"/>
**Sep-Nov 1934
***Submarine eruption with [[pumice]]
**7 Dec 1934 -Mar 1935 2&nbsp;km east of Tokara-Iwo-Jima<ref name="gbank"/>
***New island [[Shōwa Iōjima]] (Shin-Io-jima) with [[lava]] finally stabilised 19 January 1935
**1997-2003 Iwo-dake<ref name="gbank"/>
***Formation and enlargement of new pit crater inside the summit crater
**Apr-Nov 1998 Iwo-dake<ref name="gbank"/>
***Ash
**May-Aug 1999 Iwo-dake<ref name="gbank"/>
***Ash
**Jan, Mar, Oct-Dec 2000 Iwo-dake<ref name="gbank"/>
***Ash 
**Feb, Apr-Dec 2001 Iwo-dake<ref name="gbank"/>
***Ash
**May-Jul 2002 Iwo-dake<ref name="gbank"/>
***Ash
**Feb, Apr-Oct 2003 Iwo-dake<ref name="gbank"/>
***Ash 
**May-Apr, Jun, Aug-Oct 2004 Iwo-dake<ref name="gbank"/>
***Ash
**3-5 May, 3-5 Jun 2013 Iwo-dake<ref name="gbank"/>
***Minor eruptions
**2 Nov 2019 Iwo-dake<ref name="gbank"/>
***Minor eruption
**29 Apr 2020 Iwo-dake<ref name="gbank"/>
***Minor eruption
**6 Oct 2020 Iwo-dake<ref name="gbank"/>
***Minor eruption
* 27 Mar 2023 – 22 Nov 2023
***Minor eruptions<ref name=GVP />