This book has 5 short sections. Read each one, answer the check, then use Next to move on — the bar above tracks how far you've come.

The map of disaster

Mark every major earthquake and volcano on a world map and something jumps out: they are not scattered at random. They trace lines — above all the great loop around the Pacific known as the Ring of Fire. Those lines are the edges of the tectonic plates. Most geological hazards happen at plate boundaries, which means proximity to a boundary largely sets the risk, and we can predict the zones where earthquakes and eruptions are likely even if we cannot say exactly when.

The type of boundary then shapes what kind of hazard you get. Convergent boundaries, where plates collide and one dives beneath another, produce the largest earthquakes, explosive volcanoes and tsunamis. Divergent boundaries, where plates pull apart, produce shallow quakes and gentler, oozing volcanism. Transform boundaries, where plates grind past each other, produce shallow quakes but little volcanism.

This also explains why some places are far safer than others. Australia sits near the middle of its plate, far from any active boundary, so it has few large earthquakes and no active mainland volcanoes — though, as we will see, "few" is not "none". The first key to geological disasters, then, is simply geography: find the plate boundaries, and you have found where the Earth is most dangerous.