|
Most volcanoes are found under the seabed. The ocean floor is very thin and can be easily pierced by magma which lies underneath, especially along the lines of weakness at plate margins. When the plates move apart, the rising magma seeps up into the gap and hardens into a new strip of crust. This type of plate margin is present in the Atlantic Ocean, making the Atlantic wider and forcing Europe and North America further apart. When new crust forms, old crust must disappear. More than half the world's volcanoes occur in a belt around the Pacific Ocean, called the Ring of Fire. They form when plates collide and old crust has been dragged back into the mantle. The buildup Underwater volcanoes are totally submerged at first. The first hint of activity can often be picked up by seismographs hich detect movements in the earth as the magma builds up. The eruption Near the surface, undersea volcanoes usually erupt violently. The hot molten lava explodes when it hits the cold sea water, producing thick, black clouds of steam and ash. Aftermath After many eruptions, the mountain breaks through the surface like te tip of an iceberg. Back (eruption) | Next (Affecting us?) |