Midagahara

Geography & Climate

Midagahara is located in Japan, within the Nankai Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 36.57° N, 137.59° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. At 2,621 meters above sea level, Midagahara rises above the surrounding terrain into montane or subalpine conditions. The elevation creates distinct ecological zones along its flanks, from forested lower slopes to exposed rocky terrain near the summit. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Midagahara sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Japan near Midagahara, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Midagahara has 6 recorded eruptions in the geological database, spanning from 7300 BCE to 1839 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1839 CE, reaching VEI 2 on the Volcanic Explosivity Index. This eruption frequency indicates a moderately active volcanic system with periodic reawakenings.

Significance

With 6 recorded eruptions on file, Midagahara has enough documented activity to help scientists identify patterns in its eruptive behavior.

GVP Reference Summary

Midagahara volcano is a dissected andesitic-to-dacitic stratovolcano on a plateau surrounded by high peaks of the North Japan Alps. The granite-and-gneiss peak of Tateyama lies immediately to the east. Formation of a 4-km-wide erosional caldera was followed by repeated eruptions of lava and pyroclastics forming the Midagahara plateau that was later dissected by the Yukawa river. Holocene eruptions have been restricted to small phreatic explosions that formed craters. A minor historical eruption occurred in the 19th century. An earthquake swarm took place in 1990. Hot springs occur in seven locations on the floor of the poorly defined erosional caldera.

— Smithsonian Institution, Global Volcanism Program