The largest known tsunami occurred in Lituya Bay, a narrow fjord in southeastern Alaska, on July 8, 1958. The cause was a 7.8-magnitude earthquake along the Fairweather Fault, which resulted in a gigantic portion of rocky mountainside falling into the icy bay and displacing an almost incomprehensible amount of water. The size of the rockslide is thought to have been around 40 million cubic yards (30 million cubic meters), with an estimated weight of 90 million tons. The impact was heard around 50 miles (80 km) away.
In some places, the resulting wave reached a height of 1,720 feet (535 m), which is nearly the height of the One World Trade Center skyscraper in New York City. The wave washed away millions of trees, with the evidence of its maximum run-up height underlined by the loss of trees high above the entrance to Gilbert Inlet. It is classified as a megatsunami because of the sudden massive water displacement. Due to the remote location, only a few boats and buildings were damaged, though it did claim the lives of five people.
Lituya Bay had already experienced several tsunamis before the record-setting events of 1958. The most notable was in 1936, when a wave with a run-up height of 490 feet (150 m) occurred, possibly due to an undersea landslide.
As the 1958 Lituya Bay tsunami demonstrates, huge waves aren't always the most destructive or deadly. The most destructive tsunami in history occurred on December 26, 2004, as a result of a 9.1-magnitude earthquake with an epicenter near Sumatra, Indonesia. The devastation, which included waves over 100 feet (30 m) high, affected 14 countries, with nearly 230,000 people losing their lives along the heavily populated coasts.
The power of the waves:
- The literal translation of the Japanese word tsunami is “harbor wave.” Various natural phenomena can cause tsunamis, including earthquakes, volcanic eruptions, landslides, and the calving of glaciers. Though some appear as huge crested waves, others resemble a rapidly rising tide.
- The steep walls and U-shaped seafloor of Lituya Bay, coupled with its location near a fault, mean that the area is likely to see giant waves again. The probability has been calculated at a 1 in 9000 chance on any given day.
- Attempting to describe the scale of the event, geologists compared the 1958 Lituya Bay tsunami with what might have happened if an asteroid had impacted the water. Thought of another way, the amount of mountain that fell into the bay was roughly equivalent to eight million dump trucks simultaneously dropping their loads into the water.
