Coasts and Reefs

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Slide 23

Conditions necessary for reef development

Reefs also tend to preferentially form in areas where:

Little clastic sediment occurs (such sediment particles smother reef builders).

Nutrient levels are low.

Water is shallow

Slide 24

Reef zones

Reef builders are zoned in a reef according to their form (encrusting forms tend to dominate the reef crest where wave action is strongest, while more delicate branching forms are confined to deeper water zones where water action is more gentle)

A lagoon can develop behind a reef, where it is protected from

strong waves

Slide 25

A special kind of reef: atoll

An atoll is a special kind of reef that is ring-shaped and has a central lagoon. It is likely that Gilligan’s Island was set in an partially formed atoll.

Slide 26

How an Atoll Forms

An atoll is formed first as a reef that fringes a volcanic island.

As the island sinks (after volcanic activity has ceased and the crust has cooled, becoming denser), the reef continues to build upward, eventually ending up as a ring-shaped structure.

Gilligan’s Island ?

Slide 27

Bikini Atoll

Bikini atoll (central Pacific) is a famous nuclear testing site

(the US tested atomic bombs here in the 1940s and 1950s)

So it makes sense that the “new swimsuit for the atomic age”

was named…guess what.

Slide 28

…And we end up back at the beach

The bikini

Enjoy your break !

Slide 29

END OF LECTURE