Qualla: 1984 Nagano Earthquake

1984 Nagano Earthquake: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430), CC BY-SA 3.0. The inn owner rode a tatami mat down the mountainside. In the Matsugoe District of western Nagano Prefecture, on the morning of September 14, 1984, the ground lurched at 8:48 a.m. local time and the slope above a small inn simply let go. The building disintegrated, the road beneath it collapsed, and the mass of earth, timber, and debris slammed into a concrete factory at the bottom of the valley, killing thirteen people. The innkeeper, somehow still alive on her mat amid the sliding wreckage, climbed a raw cliff of freshly exposed earth despite severe injuries. She was found and hospitalized for two weeks. Her survival was one small miracle in a disaster that killed or claimed at least 29 people and reshaped the flanks of Mount Ontake.

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Image: photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430) | CC BY-SA 3.0

1984 Nagano Earthquake: Eight Forty-Eight in the Morning

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Mikenorton, CC BY-SA 3.0. The earthquake registered magnitude 6.3 and struck the western part of Nagano Prefecture. The epicenter was shallow, though no visible surface fault appeared. The Japan Meteorological Agency later determined that two subsurface faults had ruptured simultaneously. A seismometer in...

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Image: Mikenorton | CC BY-SA 3.0

1984 Nagano Earthquake: A Mountain Unraveling

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit photo: Qurren (talk), with IXY DIGITAL 10 compact digital camera., CC BY-SA 3.0. The most catastrophic landslide erupted from the south face of Mount Ontake, an active stratovolcano rising 3,067 meters in the Kiso Mountains. An estimated 3.45 million cubic meters of earth broke free and accelerated to speeds between 80 and 100 kilometers per hour, a wall of r...

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Image: photo: Qurren (talk), with IXY DIGITAL 10 compact digital camera. | CC BY-SA 3.0

1984 Nagano Earthquake: Whispers Before the Shaking

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430), CC BY-SA 3.0. Scientists at Nagoya University later discovered that the earth had been signaling its intentions. Hot spring observatories near the epicenter had recorded unusual shifts in the ratio of methane to argon in groundwater, along with spikes in dissolved hydrogen, in the period befor...

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Image: photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430) | CC BY-SA 3.0

1984 Nagano Earthquake: Rebuilding Against the Next Time

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430), CC BY-SA 3.0. The village of Otaki bore the brunt of the destruction, with 87 homes destroyed. In the years following the disaster, engineers constructed nine check dams on Mount Ontake's slopes, massive concrete barriers designed to catch and slow future debris flows before they could reach i...

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Image: photo: Qurren (talk) Taken with Canon IXY DIGITAL 450 (Digital IXUS 430) | CC BY-SA 3.0