The Hawaiian island chain is located in the Pacific Ocean. It is formed of volcanoes and the active ones are at the south-east tip of the archipelago, where Hawaii itself is located.
It is believed that the chain began to form nearly 80 million years ago. Each island started to evolve after an eruption on the sea floor. First, a ‘hot spot’ existed on the ocean bed, which let out a plume of material called magma. This magma may originate as deep as 2,883 kilometres below the ocean bed. Next, further eruptions took place, which built up the volcano. Eventually it emerged above the surface of the ocean.
Since that time, the spume of magma has remained static as the Pacific tectonic plate moves in a north-west direction across it at a speed of 7-9 centimetres per year. As it moves, a volcano forms as it passes over the hotspot and then becomes inactive when it has passed it.
(159 words)
Para 1 – describes the subject or topic of the question.
Para 2 – describes how a volcano is formed in the sea.
Para 3 – explains why a chain of active and inactive volcanoes has formed.
No comments:
Post a Comment