07

Nov

2014

The Tragedy at Mt. Ontake (Ontake-san), Japan

Written by: Grant Heiken

 
Mount Ontake, Japan, aerial view of gases emerging from crater

An Explosion in Japan

Grant Heiken, the author of Dangerous Neighbors, discusses the recent eruption of Mt. Ontake.

 

Mount Ontake is a 3,076-m-high (10,062 ft) sacred mountain located in central Honshu, about 200 km west of Tokyo. The volcano is popular with hikers and pilgrims, and hundreds of visitors were near the summit on a beautiful fall Saturday, September 27, 2014. Although Ontake was thought to be dormant, there have been intermittent phreatic (steam) eruptions there since 1979.

Many young volcanoes have active geothermal systems. Every now and then one these systems explodes, ejecting steam, mud, and rocks. An example of this type of activity occurred at Soufrière de Guadeloupe, French Antilles, in 1976. The Soufrière eruption continued intermittently for several months and triggered the evacuation of thousands of residents from towns adjacent to the volcano. Typically during an eruption that follows the rise of magma to the surface of a volcano a series of earthquakes occurs below the summit that can be tracked and there is surface deformation.  If these geophysical phenomena can be monitored and emergency warnings are declared. However, before phreatic eruptions there is little if any warning.

In the case of Ontake, the phreatic eruptions caught hundreds of hikers near the summit. The muddy, turbulent clouds of fine-grained material flowed downhill, turning day into night and making breathing very difficult. More dangerous were the large rocks blown out during the eruption that carpeted the crater rim and upper slopes. Fifty-five people were killed and nine are still missing. Photographs of hikers and rescuers show that they were all coated with the sticky ash that is characteristic of phreatic eruptions.

What can be done to protect hikers on these volcanoes?  Unfortunately, not much except to remind them that there is always a risk, even on a beautiful Saturday morning.

Sources: Japan Meteorological Agency, The Smithsonian Global Volcanism Network, and various news agencies.

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About the Author: Grant Heiken

 

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