Thursday, February 3, 2011

Q21. Task 1 - Graph (Solved) (Pictorial)

The pictorial chart illustrates the information on the Hawaiian Island chain located in the center of the Pacific Ocean.

The chain is approximately 2,700 km in length. It is formed of volcanoes and the active ones are at the south-east tip of the archipelago, where Hawaii itself is located.

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 km 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 cm per year.

As it moves, a volcano forms as it passes over the hotspot and then becomes inactive when it has passed it.

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