The Earth’s crust is broken up into large chunks called plates. These plates float because of convection currents in the magma of the upper mantle.
Learn more about convection currents in Physical World 19.5
The movement of the Earth’s crust is called plate tectonics. This movement can cause volcanoes and earthquakes.
Seismology Seismology is the study of volcanoes and earthquakes.
z Fig. 22.1.2
Damage caused by the earthquake in Christchurch, New Zealand, in 2011
After an earthquake or a volcano, the ground moves because of seismic waves passing through the Earth’s crust. The more energy carried by seismic waves, the more movement there will be in the Earth’s crust.
Scientists measure the movement of the ground using a seismograph. The Richter scale describes the magnitude (size) of an earthquake in numbers from 0 to approximately 9.
The Richter scale is not a linear number scale. It is a logarithmic scale. This means that an earthquake that measures 2 on the Richter scale is 10 times bigger than an earthquake that measures 1.
Logarithmic scale
1. What are the advantages of using a logarithmic scale?
z Fig. 22.1.3
A seismograph recording the movement of the ground during an earthquake
2. What other physical quantities or natural phenomena are reported using a logarithmic scale?
Rock The Earth’s crust is made up of three main types of rock: 1. Igneous rocks 2. Sedimentary rocks 3. Metamorphic rocks.
1. Igneous rocks z 382 Fig. 22.1.4 Granite is an igneous rock
Igneous rocks form when magma breaks through the surface of the Earth’s crust during a volcano. When it cools, the magma becomes solid.
