{"id":16228,"date":"2022-08-15T00:00:00","date_gmt":"2022-08-14T22:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/?post_type=purple_issue&p=16228"},"modified":"2022-08-22T11:40:21","modified_gmt":"2022-08-22T09:40:21","slug":"how-are-atolls-formed","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/2022\/08\/15\/how-are-atolls-formed\/","title":{"rendered":"How are atolls formed?"},"content":{"rendered":"\n

How are atolls formed?<\/h2>\n\n

SUZIE SCOTT, EDINBURGH <\/p>\n\n

Atolls are ring-shaped coral reef islands in the open ocean with a central lagoon. They\u2019re found in warm, tropical or subtropical waters where corals can flourish. Of the 439 atolls in the world, most are located in the Pacific Ocean. Atolls have vibrant ecosystems, and the parts of the reef that lay above the water may even become forested. <\/p>\n\n

Both the atoll and the ecosystem can take millions of years to evolve. <\/p>\n\n

However, some scientists studying atolls in the Maldives have proposed an alternate theory, whereby cyclical changes in sea level are responsible. As falling sea levels expose a bank of organic carbonate rock, mildly acidic rain erodes it, leaving behind a depression where water can pool. As sea levels rise, corals keep pace and build up around this lagoon, forming an atoll without the need for a volcano. <\/p>\n\n

\"\"<\/figure><\/div>\n\n
Step 1<\/strong><\/h6>\n\n

An underwater volcano builds up from the seafloor and breaks above the surface of the water.<\/p>\n\n

\n\n
\"\"<\/figure><\/div>\n\n
Step <\/strong>2<\/h6>\n\n

As the volcano goes extinct, or becomes temporarily dormant, algae and coral start to colonise the shore, forming a fringing reef. <\/p>\n\n

\n\n
\"\"<\/figure><\/div>\n\n
Step <\/strong>3<\/h6>\n\n

Erosion or a subsiding oceanic plate causes the volcanic island to sink into the ocean. As it does so, a lagoon starts to form between the reef and the volcano. Meanwhile, the coral and algae keep pace, continuously building up the reef as it becomes a barrier reef. <\/p>\n\n

\n\n
\"\"<\/figure><\/div>\n\n
Step <\/strong>4<\/h6>\n\n

When the volcanic island disappears, having become completely submerged below the water, it leaves behind a lagoon protected by the barrier reef; an atoll of coral limestone composed of calcium carbonate. <\/p>\n\n

<\/div>
\n

Email your questions to<\/span>
questions@sciencefocus.com<\/a>
or submit on Twitter<\/span>
@sciencefocus<\/a><\/p>\n<\/div><\/section>\n\n

ILLUSTRATIONS: DANIEL BRIGHT<\/p>\n","protected":false},"excerpt":{"rendered":"

How are atolls formed? SUZIE SCOTT, EDINBURGH Atolls are ring-shaped coral reef islands in the open ocean with a central lagoon. They\u2019re found in warm, tropical or subtropical waters where corals can flourish. Of the 439 atolls in the world, most are located in the Pacific Ocean. Atolls have vibrant ecosystems, and the parts of […]<\/p>\n","protected":false},"author":24,"featured_media":16574,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"83","purple_custom_meta_purple_page_number":"83","purple_seq_number":"2","purple_custom_meta_purple_seq_number":"2","purple_source_article":"article_83-2.xml","purple_custom_meta_purple_source_article":"article_83-2.xml","purple_source_issue":"August-2022","purple_custom_meta_purple_source_issue":"August-2022","purple_external_id":"August-2022-83-2","purple_custom_meta_purple_external_id":"August-2022-83-2","purple_issue_code":"|0000089657||","purple_custom_meta_purple_issue_code":"|0000089657||","purple_android_product":"com.focus.magazine.issue381","purple_custom_meta_purple_android_product":"com.focus.magazine.issue381","purple_ios_product":"com.focus.magazine.issue381","purple_custom_meta_purple_ios_product":"com.focus.magazine.issue381","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"0f422ad1-c939-476d-9f82-a410052ad4c3","purple_migrated":"","kt_blocks_editor_width":"","apple_news_api_created_at":"2022-08-15T15:42:34Z","apple_news_article-theme":"","apple_news_api_id":"7425dac1-a0d6-47bf-9235-a77c9fa7e0d7","apple_news_api_modified_at":"2022-08-22T09:40:28Z","apple_news_api_revision":"AAAAAAAAAAAAAAAAAAAABg==","apple_news_api_share_url":"https:\/\/apple.news\/AdCXawaDWR7-SNad8n6fg1w","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":true,"apple_news_is_preview":true,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_article_theme":"","apple_news_sections":"[]"},"categories":[30],"tags":[15],"apple_news_notices":[],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"2","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1.jpg",1000,871,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1-300x261.jpg",300,261,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1-768x669.jpg",768,669,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1.jpg",800,697,false],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1.jpg",1000,871,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/Atolls-1.jpg",1000,871,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"How are atolls formed? SUZIE SCOTT, EDINBURGH Atolls are ring-shaped coral reef islands in the open ocean with a central lagoon. They\u2019re found in warm, tropical or subtropical waters where corals can flourish. Of the 439 atolls in the world, most are located in the Pacific Ocean. Atolls have vibrant ecosystems, and the parts of…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16228"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/comments?post=16228"}],"version-history":[{"count":10,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16228\/revisions"}],"predecessor-version":[{"id":16852,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16228\/revisions\/16852"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media\/16574"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media?parent=16228"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/categories?post=16228"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/tags?post=16228"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}