Earthquakes,Volcanoes,and Tsunamis

Earthquakes, Volcanoes, and Tsunamis

Introduction The ground and the ocean are usually peaceful. But forces deep within the earth can suddenly cause earthquakes, volcanoes, and tsunamis (tsoo-NOM-ees). In this book, you will read about these events and the forces that cause them.

Deep Within the Earth The top layer of Earth is made of giant pieces of rock, like the pieces of a puzzle. The pieces of rock, called plates, make up continents and ocean floors. Where the plates come together, there are often cracks and gaps, called faults.

Underneath the plates, the Earth is very hot. It is so hot that rock melts into a liquid called magma. The plates float on top of this liquid magma. The magma is always moving, dragging the plates around with it. At the edges of the moving plates, three different things can happen. If the plates are moving against each other, one plate slides over or under the other plate (Fig. 1). If the plates are moving past each other, the edges of the plates grind together (Fig. 2). And if the plates are moving apart, they make a gap where magma comes out (Fig. 3).

Earthquakes: Terrible Trembling Sometimes the plates get caught on each other and cannot move. The pressure and energy build up. Then, suddenly, the rocks give way. The ground shakes. Far above, people feel an earthquake.

Some earthquakes are small and harmless. But sometimes the shaking is so strong that buildings crumble, bridges collapse, and large cracks open in the ground.