On May 22, 1960, the most powerful earthquake ever recorded struck southern Chile. It measured 9.5 on the magnitude scale. The shaking lasted about ten minutes. Entire towns were demolished. Landslides blocked rivers and created new lakes. The earthquake happened because of a process deep underground. Earth's outer layer is made of giant pieces called tectonic plates. These plates move very slowly, but sometimes they get stuck. Pressure builds up for years. When the plates suddenly slip, the stored energy is released as an earthquake. Chile sits on the boundary between two major plates. The Nazca Plate pushes under the South American Plate. This zone is called a subduction zone. The 1960 earthquake released so much energy that it also caused tsunamis. Giant waves traveled across the Pacific Ocean at the speed of a jet plane. The waves reached Hawaii fifteen hours later and Japan twenty-two hours later. About 1,600 people died in Chile. Scientists still study this earthquake to understand how massive earthquakes work and how to prepare for them.