It was demonstrated that submarine mega mass wasting due to quite recent submarine eruptions (possibly including the Teisi Knoll eruption in 1989) should have occurred along the eastern continental slope of the Izu Peninsula, central Japan. Large area of the slope failed, and turbidite and debris flow deposits partially covered the sea bottom near Hatsushima Island, where deep-sea clam communities are associated with fluid venting and high heat flow. The catastrophe was evidenced from turbidite sequences having pumice fragments and shallow water benthic foraminifers, heat flow values, and side-looking sonar image including large scale of flow mountains. Significant increase of bottom depth since 1982 was observed as well as chaotic multi-ecograms of PDR both northward and southward from the deep-sea clam community site along the foot of the escarpment with a length of about 10 km.
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