Understanding Atolls

The video tutorial explains the concept and formation of atolls, which are ring-shaped coral reefs surrounding a lagoon. It begins with a trip announcement to an atoll in Ahe and proceeds to define what an atoll is. The formation process is detailed, starting with volcanic eruptions that create islands, which eventually sink due to erosion and rising waters. Coral reefs form around the sinking island, leading to the creation of a lagoon. The final structure of an atoll is a ring of sand with a lagoon in the center and the ocean outside. The video concludes with a reflection on the historical presence of a volcano beneath the lagoon.

What is the basic structure of an atoll?

• A desert with an oasis

• A mountain surrounded by a forest

• A ring of sand and dead coral with a lagoon in the center

• A plain with a river running through it

What is the initial step in the formation of an atoll?

• A glacier melts to form a lake

• A volcanic eruption creates an island

• A sand dune is formed by the wind

• A coral reef forms in the ocean

What happens to the volcanic island over millions of years?

• It grows larger due to more eruptions

• It remains unchanged

• It collapses due to weight, erosion, and rising waters

• It turns into a desert

How is a coral reef formed around a sinking island?

• By the accumulation of sand

• By the growth of coral animals welding together

• By the deposition of volcanic ash

• By the movement of tectonic plates

What remains after the volcano is completely submerged?

• A barren rock

• A mountain peak

• A dense forest

• A strip of sand with a lagoon in the center

What is the body of water called that forms between the island and the reef?

• A river

• A pond

• A lagoon

• A bay