Out in the middle of the ocean, tsunamis, fast-moving waves resulting from an earthquake, are generally mild, reaching heights of about 3 or 4 feet (1 to 1.2 meters).
As the ocean waves approach the shallower water of the shore, the rising sediment rapidly slows them down from about 600 to 100 miles per hour (960 to 160 kilometers). The force of the incoming waves creates a wall of water that may extend 200 feet (61 meters) high.
As the wall crests and crashes along the coast, houses, public buildings, and great ships can be splintered like matchsticks or carried miles ashore.
Streams and rivers leading inland cannot hold the massive influx of water and flood their banks.
On April 1, 1946, the tsunami created by the Aleutian Islands earthquake in Alaska traveled 2,000 miles (3,200 kilometers) in 4 hours to the island of Hawaii.
Waves that were 4 feet (1.2 meters) high in the ocean rose to SS feet (17 meters) before hitting the resort town of Hilo. The town was destroyed and 173 people died.