<P> The two types of islands are often found in proximity to each other, especially among the islands of the South Pacific Ocean, where low islands are found on the fringing reefs that surround most high islands . Volcanic islands normally arise above a so - called hotspot . </P> <P> The differences in geology and topography between high and low islands mean a lot in terms of habitability for humans: high islands above a certain size usually have fresh groundwater, while low islands often do not . This hampers human settlement on many low islands . </P>

The volcanic high islands of micronesia far outnumber the low islands