One type of volcanic oceanic island is found in a volcanic island arc. Examples are the Saint Peter and Saint Paul Archipelago in the North Atlantic Ocean and Macquarie Island in the South Pacific Ocean. The few oceanic islands that are not volcanic are tectonic in origin and arise where plate movements have lifted up the ocean floor above the surface. The vast majority are volcanic in origin, such as Saint Helena in the South Atlantic Ocean. Other definitions limit the term to only refer to islands with no past geological connections to a greater landmass. Oceanic islands are often considered to be islands that do not sit on continental shelves. Main article: High island Tectonic versus volcanic While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived. fluvial or alluvial islands formed in river deltas or midstream within large rivers.
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