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Plate destruction There is also an ocean ridge in the Pacific, called the Pacific Rise. From the ridge, one plate spreads westwards and the other eastwards. The plate spreading eastwards collides with the plate carrying South America, which is moving westwards. The lighter South American, or continental, plate rides up over the ocean plate and forces it down. As it descends, the ocean plate melts and is destroyed. This kind of boundary is called a destructive margin. Mountain building The South American plate does not escape damage during its collision with the ocean plate. It crumples up to form the towering Andes Mountains. Deep below, the ocean plate melts and red–hot rock forces its way upwards. It spurts out of the surface, creating volcanoes. As the plates grind against one another, they often lock together then suddenly become free. This sends shock waves through the rocks, causing earthquakes.

This satellite picture centers on the Atlantic Ocean. It shows clearly the Mid– Atlantic Ridge.

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The ocean ridges Where molten rock wells up along a constructive margin, a mountain range called an ocean ridge grows up. The ridge that snakes across the floor of the Atlantic Ocean is called the Mid-Atlantic Ridge. For most of its length, it is hidden beneath the waves. But it rises to the surface in the far north, where it creates the island of Iceland. Here, molten material is constantly welling up from below, forming volcanoes.

∆ Devastation caused by an earthquake in Turkey, in which tens of thousands of people died.