学习资讯 编辑：嘉馨 2017-09-26 14:23:35
The diagram shows the growth cycle of a volcanic island.
The diagram demonstrates the natural process in terms of how a volcanic island grows from beneath the sea, explodes, and then eventually sinks to become an underwater reef, which involves the following nine stages.
In the first two stages, termed as the ‘preshield’ and ‘protoshield’ stages, a mountain gradually builds under the surface of the sea. In the third(‘explosive’ phase), hydro-explosions occur, from which a cone of ash is deposited. A large number of cinder cones then pile up to form a ‘shield’ on the top of the volcano.
This shield gradually erodes and subsides to form reefs below the surface, but there are ongoing volcanic activitites including lava flows. By 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, and the process is finished.
Overall, huge volcanoes rise and fall under the sea in a natural process known as the volcanic island growth cycle.