Introduction

Volcanism is a spectacular display of the complex way in which energy and materials are exchanged between three major components of our planet: the solid Earth, oceans, and atmosphere. Mankind has long been both fascinated and terrified by erupting volcanoes. Yet throughout history people have been drawn to their fertile slopes and have developed a unique symbiosis. In many cultures, volcanoes symbolize a source of tremendous power that must be placated by worship or sacrifice. Volcanologists, on the other hand, strive to understand how volcanoes work in order to better predict their behaviour and reduce the hazards to people who live near them. But volcanoes are not merely destructive and need to be viewed as an integral part of the dynamic Earth system. They create new land, replenish soil, and provide essential water and other gases to our oceans and atmosphere. Much of this book will focus on the relationship of volcanoes to the environment and to mankind. However, before these topics are addressed we need to begin with some fundamental concepts about the causes and processes of volcanism. In this chapter we explore how volcanoes work by examining the complex path that must be taken before an eruption takes place at the Earth's surface. This includes the generation of magma at depth, its rise, storage and evolution within the Earth's crust, and finally the factors that determine the nature of the eruption at the surface.