LAUPAHOEHOE, Hawaii — Almost 70 years ago, in this one-time waterfront village, students sat in a classroom when the waves came and went with only destruction left in the wake.
An earthquake near Alaska on April 1, 1946, sent big, rolling walls of water to Hawaii. The disaster killed 159 people in the islands, including the 19 at the small village school. It was nowhere near the deadliest tsunami in history, but a poignant reminder that an earthquake can cause damage thousands of miles away.
Hawaii holds these memories close. In Hilo, the biggest city near Laupahoehoe, some 30 miles away, the Pacific Tsunami Museum provides residents and visitors with almost all the information they could want about the powerful waves that have come ashore in the state’s history.
What is a Tsunami?
Tsunamis are large waves caused by tectonic activity. When earthquakes occur or volcanoes erupt near water, the strong vibrations can pass through the water causing massive waves known as tsunamis.
Generally, most tsunamis are never felt on land. They are either slightly larger than normal waves, or the energy from the event is shifted off into uninhabited areas of the ocean, and dissipates along the way.
Sometimes, however, a powerful tsunami is directed toward land and waves have been known to reach 10 meters (33 feet) high. These huge waves sweep over beaches and travel inland, unleashing their powerful force on towns and cities.
What Causes a Tsunami?
So what exactly causes these giant waves? Well, like the Hawaii disaster of 1946, an earthquake is the culprit.
The planet has more than a dozen tectonic plates, pieces of the earth that at times shift and move because below them the mantle — and nearer the core, the molten — are not nearly as solid as the plates. Convection currents, or heat transfers, cause the plates to smash into each other, pull apart, or reposition themselves atop of one another, and the impact sends powerful shock waves through the earth.
Now add water to the equation. Think about sitting in a bathtub and moving your legs back and forth as if you were making a snow angel. The water begins to ripple, and the faster you move your legs, the bigger and stronger these ripples get.
This type of force, during an earthquake, is tens of millions of times stronger, thus the waves they generate can become much bigger. They might start as long waves only inches high, however as they get closer to shore, the shallow water forces the water into a high wave.
Volcanoes are another source of tsunamis, however, this is a much more rare occurance.