The Vestmannaeyjar volcanic system has been moderately active in the Holocene with the latest eruption occurring in 1973. The system is 30-35 km long and 20-25 km wide, forming an archipelago 10-30 km off the south coast of Iceland reaching a maximum elevation of 283 m. The archipelago consists of about 15 islands and 30 skerries that are the remains of volcanic craters and islands dating back through late Quaternary to the early Holocene.
Vestmannaeyjar can be classified as an embryonic central volcano without a clearly developed fissure swarm. Eruptions are explosive phreatomagmatic or strombolian coupled with effusive lava formation. The system has only produced basalt.
Activity appears to be episodic, with the last episode including the formation of the island of Surtsey in 1963-67, 1 km3 of tephra and lava, and the eruption of Eldfell in 1973, 0.25 km3 of mostly lava. The 1973 eruption occurred on the populated island of Heimaey, with the eruption fissure only 200 m away from the nearest houses. The long term eruption frequency is poorly known but is of the order of one eruption every 1000 years.