<ul><li>The plates at a constructive boundary move apart because of the convection currents. </li></ul><ul><li>Magma rises from the mantle and erupts as the plates slowly move apart. </li></ul><ul><li>The magma cools and solidifies into igneous rock when it reaches the surface, and the process is repeated. </li></ul><ul><li>This new rock builds up to form a volcano over a long period of time. </li></ul><ul><li>Some of these volcanoes become so large that they form islands of their own. </li></ul>Volcano Helgafjell near Iceland What happens there?
An example of a constructive plate boundary <ul><li>Constructive plate boundaries are found in many different places around the world such as in the middle of the Atlantic Ocean, the Indian Ocean, and in the Eastern Pacific Ocean. </li></ul><ul><li>The plate boundary running through the middle of the Atlantic Ocean is called the Mid-Atlantic Ridge. </li></ul><ul><li>This ridge rises above sea-level in several areas along its surface area, but the place were it rises above the most is the volcanic island of Iceland . </li></ul>
<ul><li>As Iceland has formed on a constructive plate boundary, its total surface area has grown by 6m in the last 20 years. </li></ul><ul><li>The ridge has caused several offshore volcanoes that have had eruptions that have caused islands to be formed, such as the islands of Surtsey and Heimaey. </li></ul><ul><li>There is almost certainly a volcano erupting on Iceland at all times because of the plate boundary. </li></ul>
<ul><li>In 1973, a major eruption occurred on the island of Heimaey, Iceland. The volcano, Eldfell, which formed the island of Heimaey, was thought to be inactive until at 01:55 on the 23 rd January lava started spewing out of fissure that was 2km long only 200m away from the town of Vestmannaeyjar. The fissure extended all the way across the island and there were 40 lava fountains that were erupting lava into the sky. Just in the first 12 hours 30 million tonnes of lava and volcanic ash were released from the fissure. All 5300 residents of the island were transported to the mainland. </li></ul>
<ul><li>After two days of the eruption the volcano was only </li></ul>erupting in one place, but after 3 weeks the volcano had formed a steep crater, which collapsed burying 400 houses on the edge of the town. The volcano continued to erupt for 5 months after it started and luckily stopped just before it cut of the islands port.
<ul><li>Although the volcano had erupted 250,000,000 m 3 of material it was still quite a small eruption by the standard of the eruptions in Iceland. Many houses had been destroyed, but at the end of the year more than half of the population of </li></ul><ul><li>the island had </li></ul><ul><li>returned. </li></ul>
<ul><li>The eruption on Heimaey showed the dangers of living on a constructive plate boundary. The area of Iceland had increased by 2.2km as the Eurasian and North American plates moved further apart. </li></ul>