Moving plates can cause earthquakes to occur, mountains to rise, and valleys to fall. However, based on current evidence, large-scale earthquakes don't occur along ocean ridges. Scientists think that molten rock serves as a lubricant. In other words, the warming of rock surfaces heats up the fault line and makes the rocks softer. This might make them less likely to break and produce seismic shock.

The potential for destructive earthquakes is much greater at the subduction zones. This type of plate movement was responsible for the earthquake that struck near Sumatra, Indonesia, on December 26, 2004. This earthquake measured an incredible 9.1 on the Richter scale. Since it occurred over 18 miles below sea level, it caused a tsunami (a huge wave) to spread out from the epicenter of the quake toward nearby land. This tsunami killed over 230,000 people, making it one of the worst natural disasters in human history. The earthquake was so powerful that it actually caused the Earth to wobble on its axis by a few centimeters!