GEOLOGICAL FEATURES OF ISLANDS

There are many thousands of islands in the world’s oceans.  Of what are they composed?  Why do they exsist?  Section I indicated that the oceans’ floors are not flat.  They have trenches, valleys, hills, mountains, or volcanoes.  In other words, just like on land. Examples of these different types of islands follow.

Volcanic Islands:  Most islands in the world are volcanic and are the tips of underwater volcanos, most are dormant, but some are active. Example Hawaiian Islands.

Coral Islands:  These are coral reefs or atolls that have risen above the surface of the surrounding water. Example – Barbados and the Florida Keys.  The Florida Keys are limestone outcroppings of an ancient coral reef but a few keys are just sand bars.  In the Indian Ocean, the Maldives are Coral.

Continental Islands.  These are islands that have broken from the mainland, usually caused by rising sea levels.  Examples:  Cuba, Hispaniola, and Puerto Rico.

Tectonic Islands:  The islands are formed when plates in the earth’s crust rub against each other and push rock upward.  Example – Lesser Antilles in the Caribbean.

Sand Bar Islands.  These islands that consist of nothing but sand. Example – Outer Banks of North Carolina.

An archipelago is a line or group of related islands scattered in lakes, rivers or the ocean and is given a group name that includes all of the included islands.  Examples:  Hawaii Islands, The Marshall Islands, The Philippines, or the Florida Keys.

Sometimes an archipelago can have multiple types of islands.  Example: The Mariana Islands in the Pacific are the summits of fifteen mostly dormant volcanic mountains.  But the southern islands in the Mariana Archipelago are limestone terraces and coral reefs.