🌋VolcanoAtlas

Kikai Caldera

Japan's Hidden Supervolcanic Threat Beneath the Sea

Elevation

704 m

Last Eruption

2025

Type

Caldera

Country

Japan

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

  • Pyroclastic flows and surges
  • Large explosive eruptions (VEI 4+)
  • Ash fall and tephra deposits
  • Lahars and debris flows

Risk Level

Population at RiskHigh
Infrastructure RiskHigh
Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary
Unknown
Silica Content
Varied composition

Tectonic Setting

Unknown
Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch
Unknown
Evidence
Unknown

Eruption Statistics & Analysis

MetricValueGlobal RankingSignificance
Total Recorded EruptionsUnknownLowModerately active volcano
Maximum VEIVEI UnknownMinorLocal impact potential
Recent Activity1 years agoVery RecentCurrently active

Monitoring & Alert Status

Monitoring Networks

Japan Meteorological Agency (JMA)
Real-time seismic monitoring
Geological Survey of Japan
Geochemical monitoring
Global Volcanism Program
International eruption database

Current Status

Active
Recent volcanic activity detected. Continuous monitoring in place.

Authority Sources

Smithsonian GVP
Official volcano database
JMA Volcano Info
Japan Meteorological Agency

Related Volcanoes

All Japan Volcanoes
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Ryukyu Islands
Regional volcanoes

Other Volcanoes in Japan

Interesting Facts

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The Akahoya eruption approximately 7,300 years ago ejected an estimated 150–170 km³ of material, making it one of the three largest volcanic eruptions of the Holocene epoch.

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Pyroclastic flows from the Akahoya eruption crossed approximately 100 km of open sea to reach the southern coast of Kyushu — one of the longest over-water pyroclastic flow travel distances ever documented.

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The distinctive orange-yellow Akahoya ash layer has been identified in geological sections from Kyushu to Hokkaido, a span of over 1,500 km, making it one of Japan's most important archaeological dating markers.

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Southern and central Kyushu were effectively depopulated for several centuries after the Akahoya eruption, fundamentally altering the course of Japan's Jōmon-period civilization.

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In 1934–35, a submarine eruption within the Kikai caldera created an entirely new island, Shōwa-Iōjima, demonstrating that magma remains accessible at shallow depths.

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In 2018, scientists from Kobe University discovered a giant lava dome approximately 32 km³ in volume on the caldera floor, reigniting debate about Kikai's future volcanic potential.

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The name 'Kikai' (鬼界) translates roughly to 'demon world' or 'spirit boundary' in Japanese, reflecting the volcanic island's sulfurous and otherworldly landscape.

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Kikai's caldera is approximately 19 km wide but almost entirely submerged — only the small islands of Satsuma-Iōjima and Take-shima mark the caldera rim above sea level.

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Iodake, the active lava dome on Satsuma-Iōjima, is composed of rhyolite — the most silica-rich and potentially explosive volcanic rock type.

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A 2014 study estimated that a large-scale caldera eruption in the Kyushu region could ultimately affect over 100 million people across Japan.

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Satsuma-Iōjima's coastal hot springs are heated by volcanic activity — bathers at Higashi Onsen soak in seawater naturally warmed by the caldera's geothermal system.

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Kikai has produced 30 recorded eruptions spanning more than 6,000 years, but only the single Akahoya event reached VEI 7 — all others have been VEI 3 or below.

Frequently Asked Questions

What is the Kikai caldera?
Kikai is a large, mostly submarine volcanic caldera approximately 19 km wide, located in the East China Sea about 50 km south of Kyushu, Japan. It was formed by a catastrophic VEI 7 eruption approximately 7,300 years ago that ejected 150–170 km³ of rhyolitic material and ranks among the largest volcanic events of the Holocene. Today, the caldera rim breaks the surface as the islands of Satsuma-Iōjima and Take-shima. Ongoing mild eruptions from the Iodake lava dome on Satsuma-Iōjima confirm that the system remains volcanically active. The caldera is part of the Ryukyu Volcanic Arc, formed by subduction of the Philippine Sea Plate beneath the Eurasian Plate.
Is Kikai caldera still active?
Yes, Kikai caldera is classified as an active volcanic system. The most recent confirmed eruption occurred at Iodake crater on Satsuma-Iōjima in December 2025, rated VEI 1. Mild phreatic and phreatomagmatic explosions from Iodake have occurred repeatedly since 1988, with notable episodes in 1998–99, 2000–2004, 2013, 2019, and 2024. Persistent fumarolic activity, sulfur dioxide emissions, and discolored nearshore waters provide continuous evidence of a heat source beneath the caldera. The Japan Meteorological Agency monitors Kikai with seismometers, GPS sensors, and webcams. While the probability of a repeat caldera-forming eruption is considered extremely low, the system's ongoing activity confirms it is far from extinct.
How big was the Kikai eruption 7,300 years ago?
The Akahoya eruption of Kikai caldera approximately 7,300 years ago was rated VEI 7 on the Volcanic Explosivity Index, making it one of the largest volcanic eruptions of the entire Holocene epoch. The eruption ejected an estimated 150–170 km³ of dense rock equivalent of rhyolitic material. For comparison, the 1991 eruption of Pinatubo (VEI 6) ejected roughly 10 km³, and the 1815 eruption of Tambora (VEI 7) ejected approximately 41 km³. Pyroclastic flows traveled 100 km across the sea to reach Kyushu, and ashfall covered Japan from Kyushu to Hokkaido. The eruption depopulated southern Kyushu for centuries.
Could Kikai caldera erupt again?
Kikai caldera could theoretically produce another large eruption, though scientists consider the probability of a VEI 7 event in the near future to be extremely low — likely less than 1% per century. Ongoing mild eruptions at Iodake confirm that magma is present beneath the caldera, and the 2018 discovery of a 32 km³ lava dome on the caldera floor demonstrates continued magmatic emplacement. However, the repose interval between caldera-forming eruptions at systems like Kikai is typically tens of thousands of years. More likely in the short term are continued phreatic explosions at Iodake. The Japan Meteorological Agency continuously monitors Kikai for any signs of escalating unrest.
Where is Kikai caldera located?
Kikai caldera is located in the East China Sea at coordinates 30.793°N, 130.305°E, approximately 50 km south of the southern tip of Kyushu, Japan's third-largest island. It lies near the northern end of the Ryukyu Island chain, within Kagoshima Prefecture. The nearest major city is Kagoshima, roughly 115 km to the north. The caldera is mostly submerged beneath the sea surface, with only the small islands of Satsuma-Iōjima (3 × 6 km) and Take-shima rising above water as fragments of the caldera rim.
What is the lava dome discovered inside Kikai caldera?
In 2018, researchers from Kobe University's Ocean Bottom Exploration Center announced the discovery of a massive lava dome on the seafloor inside Kikai caldera. The dome measures approximately 32 km³ in volume and 10 km across, making it one of the largest volcanic domes known on Earth. It was detected using underwater seismic surveys, sonar mapping, and remotely operated vehicle observations. The dome's composition appears to be rhyolitic, consistent with Kikai's eruptive history. The discovery indicates that significant volumes of magma have been emplaced within the caldera since the Akahoya eruption, though scientists emphasize this does not indicate an imminent large eruption.
Can you visit Kikai caldera?
The primary way to experience Kikai caldera is by visiting Satsuma-Iōjima, the inhabited island that forms part of the caldera rim. The island is accessible by ferry from Kagoshima Port, with sailings several times per week (approximately 4 hours each way). Visitors can view Iodake's active fumaroles from safe distances, bathe in the volcanic coastal hot spring at Higashi Onsen, and explore the island's dramatic volcanic landscape. Accommodation is limited to a small number of guesthouses. Access to certain areas near Iodake may be restricted depending on the current JMA volcanic alert level. Shōwa-Iōjima and the submerged caldera itself are not accessible to visitors.
What type of volcano is Kikai?
Kikai is classified as a caldera — a large volcanic depression formed by the collapse of a magma chamber following a massive eruption. At approximately 19 km in diameter, it ranks among the larger calderas in the Japanese archipelago. Within the caldera, multiple eruption centers exist, including the Iodake rhyolitic lava dome and the Inamuradake basaltic scoria cone. The dominant rock type is rhyolite, which is highly silica-rich and associated with the most explosive eruption styles. This classification distinguishes Kikai from typical stratovolcanoes or shield volcanoes, placing it in the same category as systems like Yellowstone, Taupo, and Aira (Sakurajima).