The diagram shows the growth cycle of a volcanic island. Write a 150-word report for a university lecturer describing the main features of the cycle.

The diagram illustrates a natural process in which a volcanic island grows from beneath the

sea

, explodes, and

then

eventually sinks to become an underwater reef. The process is divided into nine stages. In the first two stages, called the ‘

preshield

Correct your spelling

shield

’ and ‘protoshield’ stages, a mountain gradually builds under the surface of the

sea

. In the

third

or ‘explosive’ phase, hydro-explosions occur which deposit a cone of ash. A large number of cinder cones

then

pile up to form a ‘shield’ on top of the volcano.

This

shield gradually erodes and subsides to form reefs below the surface of the

sea

.

However

, there may be ongoing volcanic activity including lava flows. By the time of the ‘coral atoll’ stage, the original form of the volcano has disappeared, and the whole structure sinks

further

under the

sea

during the ‘guyot’ stage. In summary, huge volcanoes rise and fall under the

sea

in a natural process known as the volcanic island growth cycle.