Picture the ground under your feet suddenly jerking sideways. Now picture it does not stop for four and a half minutes. That is what happened in Alaska on March 27, 1964. The Great Alaska Earthquake measured 9. 2 on the magnitude scale -- the most powerful earthquake ever recorded in North America. The shaking started near the city of Anchorage at 5:36 in the evening. Buildings cracked and collapsed. Streets split apart. In some places, the ground dropped ten feet in seconds. But the earthquake was just the beginning. The shaking triggered massive tsunamis -- giant ocean waves that slammed into coastal towns. The town of Valdez was nearly wiped out. Waves reached as far as California and Hawaii. Alaska sits on the "Ring of Fire." This zone circles the Pacific Ocean. Most earthquakes and volcanic eruptions happen here. The tectonic plates under Alaska are constantly pushing against each other. When the pressure gets too great, the plates slip -- and the ground shakes. After the disaster, scientists studied the earthquake closely. What they learned helped create better building codes and tsunami warning systems that protect people today.