Infographic How Islands Form Oceanic islands were never linked to a mainland. Some lie far from any continent. Many oceanic islands are formed by underwater volcanoes, while others are formed by coral reefs. Free Download Free Download Login or Sign Up for a Free Account to access this content. In order to access free content on Kids Discover Online you must either login to your existing account or sign up for a free account and login. Login to Existing Account Sign Up for an Account Learn More About Kids Discover Online