Smith Rock
"Smith Rock is a steep-sided basaltic pinnacle that forms part of the outer southern flank of a 8-9 km wide submarine caldera that truncates a 20-km-wide seamount. The caldera was formed between about 60,000 and 30,000 years ago. The Shirane dacitic central cone, 3 km wide and 800 m high, rises to within 8 m of the sea surface in the eastern side of the caldera, whose 600-700 m high walls and outer flanks expose basaltic, andesitic, and rhyolitic rocks. Two large submarine cones, Sumisu Knolls No. 1 and 2, lie west of the caldera. Submarine eruptions have been reported from a number of locations near 136-m-high Smith Rock (also known as Sumisu-jima, or Smith Island), the last of which occurred in 1916. Water discoloration has been frequently observed since the 1970s near Smith Rock. In October 1992, a 6-km-long zone of discolored water was seen extending from the shallow Shirane rock mass near the eastern rim of the caldera, which rises to within 7 m of the sea surface and is the youngest feature of the volcanic complex."  -Smithsonian Volcano Archive
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