pumice stones

伊豆大島の災害は度重なる不運も影響したとの記事です。pumice stonesは”very light grey rock from a volcano that is crushed to a powder and used for cleaning"（軽石）です。（GP）

Unfortunate factors

Unfortunate factors piled up on Izu Oshima island to cause the massive mudslide that cost many people their lives.

Typhoon No. 26, believed to be the most powerful storm in the last 10 years, brought a record 824 millimeters of rain in 24 hours to Wednesday morning, 2½ times the average monthly rainfall for October. The rainfall early Thursday morning reached 335 millimeters in three hours, the second-heaviest on record in the nation.

Although the typhoon grazed the archipelago, it overlapped with the front hovering over Oshima island, causing the torrential rain. The damage caused by the heavy rain was apparently amplified due to the geographical and geological conditions inherent to volcanic islands.

The island has a layer of impermeable bedrock topped with a layer of permeable lava, pumice stones and volca-nic ash. The torrential rain apparently triggered the collapse of the surface layer.

The surface of the mountain was gouged in many places, and mudslides with fallen logs burst into residential areas, smashing houses.

Another unfortunate factor is that neither a recommendation nor an instruction to evacuate was issued amid the onslaught of the powerful typhoon.

http://the-japan-news.com/news/article/0000730062
pumice stones