池田・山川 - Ikeda & Yamagawa Calderas - 3/10 & 3/11/2025
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池田・山川 - Ikeda & Yamagawa Calderas - 3/10 & 3/11/2025

March 11, 2025Ikeda & Yamagawa (池田・山川)2025

My Experience - The experience over this region lasted a couple of days visiting several points around the Ikeda Caldera and Lake, additionally visiting and staying the night in the van at Unagiike (Lake) and Onsen area, as well as visiting the town of Yamagawa and several points in an around Ibusuki area. (Yamagawa Caldera in foreground, Ikeda further back, with view of Kaimondake)


This overall region is in Kagoshima however geologically, volcanically, is also named according to the Ikeda Caldera, Ibusuki Volcanic Fields, and/or Ata Caldera with more details provided below.

There was not any hiking for this area specifically other than Mount Kaimondake which I hike on 3/12/2025. Most of my travels and observations in this area were largely being in the presence of specific volcanic sites and points of "my" interest. To the unsuspecting traveler or even to most inhabitants that live through the Kagoshima region, although they are familiar with the reality of living in a volcanically active region, many don't often realize the significance of the specific locations they live.


Overall, amazing trip to Kagoshima and this entire area. The people were incredibly friendly, more engaging in southern Japan. I found many if them to have some of the biggest, welcoming smiles and interactions.

The food of this region is also quite amazing, lots of coffee, brown cane sugar from many of the southern islands administered by and included in Kagoshima prefecture. Additionally black pork Kurobuta is well known in this area.

See also my additional post on Unagi onsen. Its an onsen that I have found many locals and Japanese across prefectures are unfamiliar with, having some of the hottest onsen waters I have ever experienced.


Demographics

  • Volcano No.- K26
  • Volcano name- Ikeda
  • Geologic code **Q3a
  • Main activity period - Holocene
  • Activity period / recent activity - ***From 6,500 yBP.
  • Latest eruption - 4,900 yBP (Nabeshima Dake)
  • Volcano type - Caldera, Lava dome, Pyroclastic cone（maar）
  • Representative rock type - Felsic
  • Main rock type ****Rhyolite, Dacite, Andesite
  • Height above sea level - 256 m (Nabeshimadake)
  • Location (Prefecture)KAGOSHIMA Latitude (WGS84)31.2347E. Longitude (WGS84)130.5642
  • Active volcano name by JMA - Ikeda and Yamagawa
  • Record of eruption & disaster - See below history...
  • Additional comments -

Source: Geological Survey of Japan (GSJ)


About

Ikeda Caldera (池田カルデラ, Ikeda karudera), is a volcanic caldera filled now with Lake Ikeda and associated with the older Ata Caldera on the Satsuma Peninsula.

The Ikeda volcano produced about 20,000 years before present the Iwamoto tephra layer found right around the region of Kagoshima Bay but not further. It later erupted Senta lava before about 7300 years ago erupting the Kikai-Akahoya tephra. The caldera-forming eruptions began 6400 years ago involving by the time they had finished about 5 km3 (1.2 cu mi) of magma and produced local pyroclastic deposits and the Ikezaki tephra. In subsequent magmatic eruptions fall deposits were created of Osagari and Mizusako scoria and Ikeda pumice. The present caldera was formed 4800 years ago when the Ikeda ignimbrite erupted that reached the eastern and western sides and southern tip of the Satsuma Peninsula. The north western wall of this caldera aligns with the Onkadobira fault scarp. This was followed by later eruptions including the Ikedako tephra and those from a fissure vent line southeast of the caldera that produced the pumiceous Yamagawa base surge. A central lava dome was formed within the caldera during the late stage of these eruptions. About 2,800 years ago on part of the margin of the caldera rim the andesitic Nabeshimadake lava dome was formed. During the caldera forming events, and after, about 2.5 km3 (0.60 cu mi) of ignimbrite and 7 km3 (1.7 cu mi) of tephra was erupted with each of the tephra deposits reaching into the Ōsumi Peninsula due to the prevailing winds.

Ikeda Caldera is associated in the Ibusuki volcanic field with the more recently active Kaimondake stratovolcano. The National Catalogue of the Active Volcanoes of Japan (JMA, 2013) includes features of the Ibusuki volcanic field as part of the Ata post-caldera system.


Ata Caldera (阿多カルデラ, Ata karudera), containing the Ata North Caldera, Mount Kaimon and Ikeda Caldera amongst other volcanoes, is a massive, ill defined, mostly submerged volcanic caldera associated with the southern portions of Kagoshima Bay.


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.


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. This eruption has been assigned a VEI of 7.5 and generated over 300 km3 (72 cu mi) of tephra. 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. There have been many more lesser eruptions.


Structure - Some of 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. This 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. 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.


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. By this definition the single caldera may be a rounded triangle about 30km in length and up to 25km in width, 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 is the Kikai Caldera. This alignment was first described by Tadaiti Matumoto in the 1940s. The alignment extends all the way north past Mount Kirishima to intersect the Aso Caldera by gravitational anomaly. The tectonic processes are rather complex in this region where the Okinawa Plate is colliding with the Amur Plate and the Pacific Plate is subducting under both.


Ibusuki Volcanic Field - The Ibusuki volcanic field, also known as the Ibusuki Volcano or Ibusuki Volcanic Group (指宿火山群), is an area of current volcanic and geothermal activity at the tip of the Satsuma Peninsula, Kagoshima prefecture, Kyushu, Japan. It is administered as part of Ibusuki City and Kirishima-Kinkowan National Park.

The Ibusuki volcanic field is at the eastern margins of the Ata Caldera and has been estimated to contain 54 km3 (13 cu mi) of volcanic material. The Ibusuki volcanic field includes the following recent active volcanoes and their vents:


Geothermal - There are about 800 hot springs within 5 km (3.1 mi) of the sea at the southeastern tip of the Satsuma Peninsula. The relatively recently commissioned Yamagawa Binary Power Station uses local geothermal power to generate up to 4990 kW.


Tectonics - The north western sector of the zone is limited by the Onkadobira fault scarp which has been interpreted as part of the rim of the Ata Caldera. The volcanism is associated with the subduction of the Philippine Sea Plate under the Eurasian Plate.


Risk - The field has both tectonic and volcanic risks. With regard to volcanic risks currently the area is in the longest period between eruptions for the last 4000 years. Earthquake swarms that do not appear to be related to the volcanoes have been described. Seismic activation of local faults in the area occurred immediately after the megathrust 2011 Tōhoku earthquake which had its epicenter 1,350 km (840 mi) away. Source: coupled together from various Wikipedia articles (on each caldera)


Geological Summary

"Ikeda and Yamagawa" is located at the southeast edge of Kagoshima Prefecture's Satsuma Peninsula. The name is used to refer to the Ikeda caldera, with a diameter of approximately 4 km, the Matsugakubo, Ikezoko, Unagiike, and Yamagawa maar group, and the Nabeshimadake lava domes at the southern rim of the Ikeda caldera. The active volcano, Kaimondake, is located to the southwest of the Ikeda caldera. The SiO2 contents of the erupted materials from those vents are ranging from 56.3 to 72.7 wt %

Source: Japan Meteorological Agency (JMA)

Tags
Caldera LakeIssieSatsuma PeninsulaKagoshimaSunamushi Onsen

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