2014 eruption of Mount Ontake

What Happened

On September 27, 2014, Mount Ontake erupted without warning at roughly 11:52 a.m. local time. The volcano, which sits on the border of Nagano and Gifu Prefectures on the island of Honshu, sent a column of ash and steam thousands of metres into the sky. Hundreds of hikers were on the mountain at the time, enjoying the autumn colours of the upper slopes.

The eruption was phreatic, meaning it was driven by groundwater flashing to steam rather than by rising magma. Blocks of rock and dense ash rained down on the summit area, and pyroclastic surges swept across the crater zone. Many of those caught on the mountain were buried under ash or struck by falling stones. Rescue efforts were hampered by continuing ashfall, toxic gas, and the risk of further eruptions.

The official death toll reached 63 people, making it the deadliest volcanic event in Japan since 1902. The eruption continued intermittently until October 14, 2014, when activity subsided enough for the alert level to be lowered. The mountain remained closed to climbers for an extended period afterward.

Background

Mount Ontake (御嶽山, Ontake-san) is a stratovolcano on Honshu, roughly 100 kilometres northeast of Nagoya and about 200 kilometres west of Tokyo. It is the second-highest volcano in Japan after Mount Fuji, and it has long been a site of religious pilgrimage as well as a popular hiking destination. Its summit area is dotted with shrines and lodges, and thousands of visitors climb it each year, particularly in the autumn foliage season.

Before 2014, Ontake had shown only minor signs of unrest. Small seismic swarms had been recorded in the years prior, and a minor eruption had occurred in 2007, but nothing suggested the scale of what was to come. The 2014 eruption began with almost no precursory activity that could be clearly identified in advance, which is characteristic of phreatic eruptions: the sudden vaporisation of groundwater can occur with little warning.

The eruption was the first fatal volcanic event in Japan since the 1991 eruption of Mount Unzen, which had killed dozens of people through pyroclastic flows. It was also the deadliest volcanic disaster in Japan since the 1902 eruption of Torishima, an island volcano south of Tokyo, which killed an estimated 150 people. In that sense, Ontake broke a long period in which Japan’s volcanoes had been relatively quiet in terms of human casualties.

Why It Mattered

The 2014 Ontake eruption forced a reassessment of how Japan prepares for volcanic emergencies. Because the mountain was crowded with hikers on a clear late-September day, the disaster struck a broad cross-section of the public rather than scientists or workers. Many of the victims were experienced climbers who had no reason to expect danger.

The event highlighted the limits of seismic monitoring for phreatic eruptions. Unlike magmatic eruptions, which often produce detectable ground deformation and increased gas output over days or weeks, phreatic blasts can occur with only minutes of warning. In the aftermath, the Japan Meteorological Agency and local governments revised their protocols for volcano alert levels and evacuation planning.

The disaster also prompted changes to how volcanic risk is communicated to the public. Ontake had been rated at alert level 1, the lowest level, on the morning of the eruption. Critics argued that the system gave hikers a false sense of security. Subsequent reforms emphasised clearer messaging about the possibility of sudden phreatic activity even at low alert levels, and encouraged the installation of more hardened shelters near popular summits.

The Name in Japanese

The Japanese name for this event is 2014年の御嶽山噴火 (2014-nen no Ontake-san funka).

• Kana reading: にせんじゅうよねんのおんたけさんふんか
• Romaji: 2014-nen no Ontake-san funka

Breaking it down:

• 2014年 (2014-nen) — "the year 2014." The kanji 年 (nen) means "year." The number is written in Arabic numerals in the standard Japanese way of expressing calendar years.
• の (no) — a possessive particle, here meaning "of" or "that of." It links the year to the eruption.
• 御嶽山 (Ontake-san) — the name of the mountain. This is read as a single unit, but each character contributes to the meaning:
• 御 (o) — an honorific prefix meaning "august" or "imperial." It is a common prefix in the names of sacred mountains and shrines.
• 嶽 (take) — "peak" or "mountain." This is the older, more formal character for "peak"; the modern simplified form is 岳. In this word it is read as take.
• 山 (san) — "mountain." Here it is read as san, the common reading for mountain names, though in other contexts it is read yama.
• 噴火 (funka) — "eruption." This is a compound of two kanji:
• 噴 (fun) — "to spout" or "to erupt," as in liquid or gas bursting forth.
• 火 (ka) — "fire." Together they literally mean "fire spouting," which is the standard Japanese term for a volcanic eruption.

So the full phrase reads literally as "the 2014 eruption of Mount Ontake," with the honorific prefix on the mountain name reflecting its status as a revered peak.

Key Figures

• Date of eruption: September 27, 2014
• End of active phase: October 14, 2014
• Deaths: 63 people
• Location: Mount Ontake, on the border of Nagano Prefecture and Gifu Prefecture, Honshu, Japan
• Coordinates: 35.8933° N, 137.4790° E
• Era: Heisei period (1989–2019), specifically the 26th year of the Heisei era (平成26年)
• Previous fatal eruption in Japan: Mount Unzen, 1991
• Previous deadlier eruption in Japan: Torishima, 1902, with an estimated 150 deaths