Itoigawa UNESCO Global Geopark is located atop a massive fault line. This location, straddling the border between the Eurasian and North American continental plates, is the reason for Itoigawa Geopark’s extreme topography, where mountains nearly 3000 meters in height plunge into the Sea of Japan.
Many of these mountains are volcanic in origin, formed of andesite, granite, porphyrite, diorite and other rocks. The youngest of these volcanoes is Mt. Yakeyama (2400 m). Born only about 3000 years ago, Mt. Yakeyama remains active to this day. Its last magma and pyroclastic flow producing eruption occurred about 300 years ago, but it has continued to produce smaller eruption events and steam explosions since then. In 1974, a phreatic eruption (steam-blast eruption) launched volcanic bombs and ash, killing 3 university students conducting field research on the mountain. The mountain experienced another phreatic eruption in 1983, but has mostly remained quiet since.
Starting in late 2015, Mt. Yakeyama has seen an increase in steam production, with steam occasionally seen stretching across the sky far to the east of the peak. Due to its active status, Mt. Yakeyama is under 24 hour surveillance and from May 1, observation equipment has detected an increasing number of volcanic earthquakes beneath the volcano.
On May 6, ash and blackened snow were detected on the east side of the peak, suggesting a minor eruption had occurred. No further eruptions have been detected, but sensor equipment have detected a slight bulging of the crust beneath Yakeyama.
In response to this increased activity, access to the area within 1 km of the mountain’s peak has been restricted. Those wishing to hike within 2 km of the peak must submit a formal climbing plan to local authorities. The Japan Meteorological Agency has not increased the warning level for the region and merely advises that visitors avoid the mountain’s peak.
As beautiful as these mountains are, it is important that we never forget the power sleeping beneath them.