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What Happens When Two Plates Push Together?

Imagine a moon-sized ball of radioactive chemicals and molten lava completely covered by seven massive pieces of solid rock. Now add a few miles' thickness of dirt, rocks and water over that and you have the makeup of the Earth. It is a constantly shifting mass trying to hold in tremendous heat and forces of the Earth's core. The constant shifting of these plates gives the Earth its features.

  1. Continental Convergence

    • Continental plates are the same density and, therefore, simply push into each other. The collision is much like two cars hitting head on. There is a lot of buckling, crumbling and folding flowing in the path of least resistance. The crushing pressure from continental plates forms mountain ranges with thickening of the plates at the collision zone. This is also the cause of shallow or surface earthquake activity releasing the intense pressure between the two plates.

    Ocean-Continental Convergence

    • Oceanic plates are thinner and more dense than continental plates. When the two plates are forced together the oceanic plate goes under the continental plate in a process known as "subduction." When the plate descends to approximately 100 miles, it begins to melt. The buoyant lava called magma slowly flows to the surface between the cracks in the two plates. Eventually the magma breaks through the surface in the form of a volcano.

    Ocean Convergence

    • When two plates push together under the ocean, one plate is subducted under the other. Since the seabed is less dense, part of the ocean floor is pulled down with the subducted plate forming a V-shaped trench on the ocean floor. Magma rising from the melted subducted plate releases volcanic debris on the ocean floor. Island volcanoes, are formed over millions of years in this way. The stress from the two plates eventually causes an earthquake that sometimes spawns a tsunami.

    Divergent Boundaries

    • When two plates push together, two plates come apart at the other end of the shifting plate. Magma pushing up from the earth's core forms a new crust changing the ocean floor. The Mid-Atlantic Ridge is one example of this, extending from the Arctic Ocean to beyond Africa's southern tip. The ocean floor moves apart at a rate of 2 1/2 inches a year with magma continually pushing upward till finally cooled by the water.

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