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Seismic unrest (1 and 2) and slight inflation (3) at Niigata Yake-Yama (source: JMA)
An increase in small earthquakes has been detected under the volcano located on the border between Niigata and Nagano Prefecture recently.
In addition, a slight increase in fumarolic activity on the eastern side of the summit crater was noted and some inflation of the volcanic edifice recorded.
According to the Niigata Meteorological Observatory monitoring the volcano, the number of volcanic earthquakes has been up to 4 times that of normal background levels, with up to 23 quakes recorded on a single day. Seismic activity has been dominated by low-frequency earthquakes, which are thought to reflect internal fluid movements (gasses, hot watery solutions, as well as magma).
While the observed unrest is far from at alarming levels, they might reflect a change in the internal hydrothermal and /or magma storage system and could (but not necessarily must) be precursors to new activity at the surface.
The alert level of the volcano remains at the lowest level (1 out of 5), but because of the uncertainty involved with the observed signs of unrest and a probably elevated risk of sudden explosions, the local government has set an exclusion zone inside a radius of 1 km around the summit.
After all, Niigata Yake-Yama is one of Honshu’s most active volcanoes with frequent eruptions in the past centuries, including a VEI 4 explosive eruption in 887 AD that produced large pyroclastic flows that reached the Japan Sea.
Steaming from the summit crater (NHK)
Courtesy of volcanodiscovery.com
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