The geology of Bouvetøya (Bouvet Island)
Bouvetøya (Bouvet Island), about 10 km long and 7.5 km wide with a 2 x 3 km large caldera (volcanic crater) in the northwestern part of the island. The highest peak is Olavtoppen which reaches 780 m a.s.l. About 95 % of the island is glaciated.
Bedrock is exposed along the coast and in the cliffs just above the surf zone. Exposed cliffs in the north and west reach heights of 500 m, and it is here most wave erosion takes place because of the constant westerly winds. This also explains the asymmetrical shape of the island; the volcanic cone is only preserved in the south and east.
The island is located on the southernmost part of the Mid-Atlantic Ridge, just east of the Bouvet triple junction – a point where three oceanic rift systems converge. The Earth's crust beneath the island is some 4.5-5 million years old, and the oldest bedrock dated above sea level is around 1.4 million years old.
The bedrock on Bouvetøya consists of two formations. The lower, oldest one mainly comprises pyroclastic rocks, which were most probably formed as submarine hyaloclastite. The youngest, upper formation consists of lava and small amounts of volcanoclastic deposits. The volcanic rocks are chiefly basaltic in composition, but the youngest lava flows are rhyolitic. Kapp Valdivia consists of a younger rhyolitic lava dome
The present volcanic activity is confined to fumaroles which occur in many places on the northern and northwestern coasts, which are closest to the caldera. There are no historical accounts of volcanic eruptions. Nyrøysa, a coastal terrace in the northwest, was formed between 1955 and 1958, but since the rocks there are 0.4-0.5 million years old, it is assumed to have been formed by a landslide. Other islands have been observed close to Bouvetøya, in historic times, including Lindsay Island and Thompson Island. The latter may have been destroyed by a volcanic explosion in 1895.