This document provides an introduction to natural hazards. It discusses the 1985 eruption of Nevado del Ruiz volcano in Colombia, which killed over 21,000 people and caused $200 million in damage. The document outlines various natural processes including internal processes like earthquakes and volcanoes from plate tectonics, and external processes from solar energy like storms. It defines hazards, risk, disasters and catastrophes, and discusses how human settlement can increase risk. The role of history in understanding hazards is described.