| Bayonnaise Rocks | |
| Native Name: | ベヨネース列岩 |
| Location: | Izu Islands |
| Archipelago: | Izu Islands |
| Area Km2: | 0.01 |
| Elevation M: | 11 |
| Country: | Japan |
| Country Admin Divisions Title: | Prefecture |
| Country Admin Divisions: | Tokyo |
| Country Admin Divisions Title 1: | Subprefecture |
| Country Admin Divisions 1: | Hachijō Subprefecture |
| Population: | 0 |
is a group of volcanic rocks in the Philippine Sea about 408km (254miles) south of Tokyo and 65km (40miles) south-southeast of Aogashima, in the south portion of the Izu archipelago, Japan. The rocks were discovered by the French corvette Bayonnaise in 1850, while surveying the islands south of Tokyo Bay.[1]
The rocks are the exposed portion of the western ridge of a submarine volcanic caldera, approximately 9km (06miles) in diameter at a depth of approximately 1000m (3,000feet).[2] The above sea-level portion has a surface area of approximately 0.01 square kilometers, with a summit height of 11m (36feet). and consists of three large rocks and many smaller rocks.[1]
The caldera is known to have erupted in 1869–1871, 1896, 1906, 1915, 1934, 1946, 1952–1955, 1957–1960, 1970, and 1988. The last known submarine eruption of the caldera was in 2023, which discolored the local water.[3]
On the northeast rim of the same caldera 12.8km (08miles) to the east of the Bayonnaise Rocks is a submerged reef named, which is a post-caldera cone with a depth of approximately 50m (160feet). During a submarine volcanic eruption of 17 September 1952, an ephemeral island was formed, with a height of 10m (30feet), which was created and destroyed several times by volcanic activity until completely disappearing on 23 September 1953. The following day, an eruption killed 31 researchers and crewmen aboard the Maritime Safety Agency survey ship No.5 Kaiyo-Maru. The island reappeared on 11 October, sinking again on 11 March 1954 and reappeared one more time between 5 April and 3 September 1954.[1]
Vegetation is sparse among the Bayonnaise Rocks. The islands are a resting place for migratory birds. Located in the Kuroshio Current, the area has abundant sea life, and is popular with sports fishermen.