Volcanoes, Earthquakes and Tidal Waves Notes

POINTS TO REMEMBER

•      Volcanoes are usually in the form of conical mountains.

•      Magma is liquid rock inside a volcano.

•      Lava is liquid rock (magma) that flows out of a volcano.

EARTHQUAKES

•      Earthquakes are the shaking, rolling or sudden shock of the Earth’s surface.

•      They are the Earth's natural means of releasing stress.

•      They are caused by severe shock waves that travel through solid rocks from underground to the surface.

•      Earthquakes can be felt over large areas although they usually last less than one minute.

•      Earthquakes cannot be predicted.

•      The point under the ground where the earthquake begins is called the focus and the corresponding spot on the surface is called the epicentre.

TIDAL WAVES

•      Tidal wave is the common name for a tsunami.

•      Tsunami is a Japanese word meaning 'harbour wave'.

•      A tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic explosion.

•      Tidal waves aren’t really waves.

•      They are ocean surface waves (wind waves) that move higher onto the shore because of the gravity of the moon.

•      The Earth’s gravity helps us to stay on the Earth and not float up into space.

•      The moon’s gravity pulls on the Earth’s water.