Iwabone is a boat site on the western side of Jogashima, facing Sagami Bay, where rugged rock layers rise from the depths almost to the surface. The warm Kuroshio Current reaches it and carries in rare species seldom seen in Tokyo Bay, and divers come for the layered rock and its large pelagic visitors.
0Where it is and how deep
35.1380° N, 139.6020° EApproximate position — the dashed circle shows where the site lies; your operator's briefing has the mooring.
The dive
The rock formations climb from a base at 30 m to near the surface. The deep highlight is the Mille-Feuille Fault, a ridge 10 m tall that begins around 26–27 m. Crevices along the rock, such as the shark hole, hold banded dogfish and Japanese bullhead sharks at rest, while eagle rays, flounders over 1 m long and schooling fish pass in the open water.
Marine life and season
- Eagle rays
- Reef fish swarms
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Good | Good | Good | Good | Good | Good | Good | Good | Good | Prime |
Season follows Miura Peninsula: Boats run all year; winter is the peak for nudibranchs and lumpsuckers, summer for colourful seasonal visitors.
Questions divers ask
How deep is the Mille-Feuille Fault at Iwabone?+
The ridge starts around 26–27 m and stands 10 m tall, so reaching its foot is a dive for Advanced Open Water divers.
Sources
- Diving in Miura and Shonan — PADI
- Kanagawa diving guide — Japan National Tourism Organization
- Jogashima Diving Points — Jogashima Diving Center
- Jogashima lighthouse — OpenStreetMap
Photo credits
- Flat layered rock shelves enclose a calm blue inlet under a clear sky, with grass in the foreground by Aspere, CC0, via Wikimedia Commons
More dive sites in Miura Peninsula
Pinnacle
Soft corals blanketing the walls of the northern drop-off
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