3 - 18 Pyroclastic flow deposits (Part 2)

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The pyroclastic flows in the 1990 - 1995 eruption of Mt. Fugen were caused by the collapses of the lava domes containing a lot of vesicles (bubbles) of high-pressure gas. The rate of the volume of vesicles to the total volume of the lava is 15-20%. The flows consisted of a mixture of the released gas and volcanic ash ran down along the valley at a very high speed. The following pictures show the pyroclastic flow deposits in its forefront.
These pictures were taken on 1 June 1991 at the upstream of the Mizunashi River. When we took them, we felt the radiant heat from the deposits. Trees stood in the area of the flow were completely destroyed, and the deposits at the forefront were accumulated about 2m high. (Photo #1, #2)
Behind the forefront, there accumulated blocks, volcanic ash, and burned fallen timber. (Photo #3, #4, #5)
The size of some blocks were larger than 1m in diameter. It was still too hot to touch with our hand. Gas is being emitted from the ash. (Photo #6)
Sulphur sedimented (settled) around the vent of the gas. (Photo #7)
The pyroclastic flows were accompanied by high-temperature glowing cloud originated with the gas released from the lava. It reached higher and further than the flow itself, and burned tall trees around. (Photo #8, #9)

A large-scale pyroclastic flow occurred two days after we had taken these pictures. It reached further downstream, and killed 43 persons.

Photo #1 Photo #2

Photo #3 Photo #4

Photo #5

Photo #6 Photo #7

Photo #8 Photo #9

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