The generally flat surface of the ocean floor is
interrupted in places by seamounts, underwater
volcanoes located over isolated hotspots. Seamounts
may be wholly submarine or may build up above
water as volcanic islands, such as the Hawaiian
island chain in the central Pacific. As subaerial volcanoes
they can be important sources of volcaniclastic
sediment to ocean basins. The flanks of the volcanoes
are commonly unstable and give rise to very largescale
submarine slides and slumps that can involve
several cubic kilometres of material. Bathymetric
mapping and sonar images of the ocean floor around
volcanic islands such as Hawaii in the Pacific and the
Canary Islands in the Atlantic have revealed the
existence of very large-scale slump features. Mass
movements on this scale would generate tsunami
(11.3.2) around