An official website of the United States government.								Here's how you know we're official.				

##### dot gov icon**Official websites use .gov**

A **.gov** website belongs to an official government organization in the United States.

##### https icon**Secure websites use HTTPS**

A small lock or **https://** means you’ve safely connected to a .gov website. Share sensitive information only on official, secure websites.

National Ocean ServiceNational Oceanic and Atmospheric Administration

              -  Home 
              -  Ocean Facts 
              -  TOPICS ****                  - Explore All Topics
                - Careers
                - Economy
                - Ecosystems
                - Geodesy
                - Hazards
                - Navigation
                - Observations
                - Ocean
                - Recreation
                - Sea Level Rise 
                - Story Maps
                - Tools 
              -  Education 
              -  News 
              -  Podcasts 
              -  Video 
              -  Images 
              -  About Us 

HomeEducationCoralsHow Do Coral Reefs Form?

# How a Coral Atoll Forms

This animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple) begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll. The process of atoll formation may take as long as 30,000,000 years to occur. Research continues into how coral atolls form.

### Corals Lessons

              - Welcome
              - What are Corals?
              - Zooxanthellae What's That?
              - How Do Stony Corals Grow?
              - How Do Coral Reefs Form?
              - Where Are Coral Reefs Found?
              - How Do Corals Reproduce?
              - Importance of Coral Reefs
              - Natural Threats to Coral Reefs
              - Anthropogenic Threats to Corals
              - Coral Diseases
              - Protecting Coral Reefs
              - References
              - Roadmap to Resources 
              - Subject Review (PDF)

----

National Science Teaching Association (NSTA)

###### **Search** Education

###### Get **Social**

Contact Us

            - Provide Feedback 
            -  Contact Us 
            -  Report an error 

##### Science. Service.Stewardship.

###### 						About NOS 					

            - About Us
            - NOS Program Offices
            - Media Inquiries
            - Website Acknowledgements

###### 						Resources 					

            - Site Index
            - Disclaimer
            - Freedom of Information Act
            - Accessibility

###### 						More Resources 					

            - Information Quality
            - Privacy Policy
            - NOS For Employees
            - USA.gov

          -  National Ocean Service
          -  National Oceanic and Atmospheric Administration
          -  Department of Commerce

##### 						Social 					

            - 
            - 
            - 
            - 
            -