This course, Volcanoes, earthquakes and tsunamis, discusses the various hazards posed by volcanic eruptions, illustrated by examples from recent eruptions. While you read this course and complete the activities afterwards, it would be a good idea to compile your own table of hazards, with as many examples of each one as you can find. You will meet the term 'micrometre' in connection with the size of very tiny ash particles; a micrometre is one-millionth of a metre, which is one-thousandth of a millimetre.