Mount Unzen, Nagasaki Prefecture, Japan.
Japan Coast Guard
Attribution
Unzendake - Kirishima, the Database of the Maritime and Submarine Volcanoes (<a rel="nofollow" class="external text" href="http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo27-2.htm">Link here</a>).