Asamayama

Honshu's Most Active Volcano

Elevation

2,568 m

Last Eruption

2019

Type

Complex volcano

Country

Japan

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

Lava flows and fountaining
Volcanic gas emissions
Local explosive activity

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

Metric	Value	Global Ranking	Significance
Total Recorded Eruptions	Unknown	Low	Moderately active volcano
Maximum VEI	VEI Unknown	Minor	Local impact potential
Recent Activity	7 years ago	Very Recent	Currently 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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Interesting Facts

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Asamayama's 145 recorded eruptions make it the most prolific erupting volcano on Honshu, Japan's main island, and one of the most frequently active volcanoes in the world.

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The 1783 Tenmei eruption killed over 1,400 people — the pyroclastic flow buried the village of Kanbara, killing 477 of its approximately 570 inhabitants.

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The VEI 5 eruption of 1108 CE was the largest eruption of the modern Maekake cone and is classified as a Plinian event comparable to the 79 AD eruption of Vesuvius.

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Asamayama sits at the unique tectonic junction where the Izu-Marianas volcanic arc meets the Northeast Japan volcanic arc.

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The Onioshidashi lava flow from the 1783 eruption remains largely unvegetated after more than 240 years and is now preserved as a volcanic park.

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Asamayama is located just 140 km from central Tokyo — a VEI 5 eruption could deposit significant ashfall on the world's most populous metropolitan area.

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The modern summit cone (Maekake) was built east of the remnants of Kurofuyama, an older volcano destroyed by a massive landslide approximately 20,000 years ago.

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During the 18th century alone, Asamayama produced 29 recorded eruptions — an average of one eruption approximately every 3.4 years.

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The 1783 eruption coincided with the severe Tenmei famine that caused widespread starvation across Japan.

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Asamayama overlooks Karuizawa, one of Japan's most fashionable resort towns and a popular Shinkansen day trip from Tokyo.

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The volcano has been referenced in Japanese literature since at least the 8th century, appearing in the Man'yōshū compiled around 759 CE.

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JMA's monitoring network around Asamayama includes broadband seismometers, GPS sensors, tiltmeters, infrasound arrays, gas analyzers, and 24-hour cameras — one of the most instrumented volcanoes on Earth.

Frequently Asked Questions

Is Asamayama (Mount Asama) still active?

Asamayama is one of the most active volcanoes in Japan and on Earth. It has produced 145 recorded eruptions over more than 9,000 years, with the most recent eruption occurring on August 7, 2019. The Japan Meteorological Agency (JMA) classifies Asamayama as active and maintains one of its most intensive monitoring networks around the volcano. The summit crater continues to emit volcanic gases, and seismic activity beneath the edifice is ongoing. Given the volcano's historical eruption frequency — an average of one eruption every 2–5 years during the 20th century — volcanologists consider another eruption highly probable. Asamayama is unequivocally active and remains one of Japan's highest-priority volcanic monitoring targets.

When did Mount Asama last erupt?

Asamayama's most recent eruption occurred on August 7, 2019, when a sudden Vulcanian explosion sent an ash plume approximately 1.8 km above the summit crater rim. The eruption ejected ballistic blocks up to 200 m from the vent and deposited light ashfall to the east. It was classified as VEI 2 on the Volcanic Explosivity Index. JMA had raised the alert level from Level 1 to Level 2 in June 2019 following increased seismic activity and ground deformation, providing some advance warning. The eruption caused no casualties but prompted temporary trail closures. Prior to 2019, the most recent eruptions occurred in 2015 (VEI 1) and 2009 (VEI 2).

How dangerous is Asamayama?

Asamayama is considered one of Japan's most dangerous volcanoes due to its high eruption frequency, proven capacity for VEI 4–5 explosions, and proximity to large populations. The 1783 eruption killed over 1,400 people through pyroclastic flows and lahars, and a similar event today would threaten Karuizawa (population ~50,000 including tourists). A VEI 5 eruption could deposit significant ashfall on the Tokyo metropolitan area, 140 km to the southeast, potentially disrupting infrastructure for tens of millions of people. Japan maintains detailed evacuation plans and an advanced monitoring network to provide early warning.

How tall is Asamayama?

Asamayama stands at 2,568 m (8,425 ft) above sea level, making it one of the most prominent peaks in central Japan. The summit is formed by the Kamayama pyroclastic cone, capping the broader Maekake cone. For comparison, Mount Fuji — Japan's tallest volcano — reaches 3,776 m (12,389 ft), while Kusatsu-Shiranesan to the northwest stands at 2,160 m (7,087 ft). Asamayama's elevation has fluctuated throughout its eruptive history as explosive eruptions remove material and effusive eruptions add to the summit area.

What type of volcano is Asamayama?

Asamayama is classified as a complex volcano, reflecting its multi-cone, multi-vent structure encompassing several distinct volcanic edifices. The modern summit is the Maekake cone, capped by the Kamayama pyroclastic cone. The Ko-Asamayama lava dome to the east represents an earlier phase of dacitic volcanism. The remnant of the older Kurofuyama volcano is visible to the west. Asamayama's magma ranges from basaltic andesite to andesite, producing eruptions that vary from gentle Strombolian activity to powerful Plinian explosions.

What happened in the 1783 eruption of Asamayama?

The 1783 Tenmei eruption was the most devastating in Asamayama's history. Beginning May 9, 1783, the volcano produced three months of escalating explosions. On August 5, the Agatsuma pyroclastic flow swept down the northern flank and buried Kanbara village, killing 477 of approximately 570 inhabitants. The flow entered the Agatsuma River, generating a lahar that killed hundreds more downstream. Total casualties exceeded 1,400. The eruption also produced the Onioshidashi lava flow, now a tourist attraction. The event coincided with the Tenmei famine and remains the benchmark for hazard planning.

Can you visit Asamayama?

Yes, though summit access is restricted. At alert Level 1, hikers can approach within about 500 m of the crater via designated trails, but the crater itself is permanently off-limits. At Level 2 or above, the exclusion zone expands to 2+ km. The most popular attraction is Onioshidashi Volcanic Park on the northern flank, featuring the 1783 lava field, the Kannon-dō temple, and panoramic views. Karuizawa at the volcano's base is reachable from Tokyo in ~70 minutes by Shinkansen. The Asama Volcano Museum offers educational exhibits.

Could Asamayama threaten Tokyo?

While Tokyo is 140 km from Asamayama — safe from direct hazards like pyroclastic flows — a major eruption could deposit significant ash on the metropolitan area. Models for a VEI 5 eruption estimate 2–10 cm of ash could fall on parts of Tokyo under unfavorable wind conditions, disrupting transportation, water, and electricity for millions. Even VEI 3–4 events could affect aviation and air quality. The probability of a VEI 5 event in any given decade is low, and Japan's monitoring system provides significant advance warning.

How often does Asamayama erupt?

Asamayama is one of the most frequently erupting volcanoes on Earth. During the 20th century, it produced 46 recorded eruptions — roughly one every 2.2 years. The 17th and 18th centuries were even more active, with 24 and 29 eruptions respectively. In the 21st century, the pace has slowed somewhat, with six eruptions between 2003 and 2019. However, this apparent decrease is well within the range of normal variability for the volcano, and volcanologists expect the current inter-eruptive interval to end with renewed activity in the coming years.

What is the Onioshidashi lava field?

Onioshidashi (literally 'demon push-out rock') is a dramatic lava field on Asamayama's northern flank, produced during the catastrophic 1783 Tenmei eruption. The blocky andesite lava covers approximately 6 km² and remains largely unvegetated more than 240 years after the eruption, creating an otherworldly landscape of jagged volcanic rock. Today it is preserved as Onioshidashi Volcanic Park, one of Nagano Prefecture's most visited geological attractions. A Buddhist temple, Kannon-dō, sits atop the lava field as a memorial to the eruption's victims. The park includes walking paths through the lava, interpretive displays, and panoramic views of the surrounding mountains.