A tsunami is a series of powerful ocean waves caused by large-scale disturbances beneath the sea surface. These disturbances, such as undersea earthquakes, volcanic eruptions, or massive landslides, displace a significant volume of water. Unlike regular ocean waves generated by wind, tsunamis possess extremely long wavelengths and periods, allowing them to travel across entire ocean basins with immense energy. While often appearing as a rapidly rising tide in the open ocean, their destructive power becomes evident as they approach coastal areas and build in height.
The Lituya Bay Megatsunami of 1958
The largest wave run-up ever recorded occurred on July 9, 1958, in Lituya Bay, Alaska, an event known as the Lituya Bay megatsunami. It was triggered by a magnitude 7.8 to 8.3 earthquake along the Fairweather Fault. The seismic activity caused approximately 40 million cubic yards of rock to plunge from 3,000 feet into the waters of Gilbert Inlet, at the head of the bay.
The massive rockfall displaced a large volume of water, generating a localized tsunami. This wave crashed against the opposite shoreline of Gilbert Inlet and ran up the steep slope to an elevation of 1,720 feet (524 meters) above sea level. This height, far surpassing that of many skyscrapers, represents the highest “run-up” documented for a tsunami.
The unique geological features of Lituya Bay, a narrow, T-shaped fjord with steep walls, amplified the wave’s height and destructive power. The impact stripped away trees and vegetation from the surrounding slopes up to the run-up height, leaving a visible “trimline.” Despite the event’s scale, some eyewitnesses aboard fishing boats in the bay survived, providing firsthand accounts.
Defining “Biggest” in Tsunamis
The term “biggest” when applied to tsunamis can be interpreted in various ways, beyond just the vertical height of the wave. Scientists use several metrics to quantify tsunami size and impact, including wave height, energy released, the area affected, and the human death toll.
Wave height itself can be measured in different ways, with “run-up” being a key measurement. Run-up refers to the maximum vertical height that tsunami water reaches on land, relative to sea level. While a tsunami’s height in the open ocean might be relatively small, it increases as the wave approaches shallower coastal waters.
The Lituya Bay event is considered the “biggest” in terms of its run-up height. However, other tsunamis, while not achieving such vertical inundation, might be considered “bigger” based on their broader impact, such as total energy released or widespread destruction and loss of life. Understanding the context of measurement is important when comparing tsunami events.
Other Notable Historic Tsunamis
While the Lituya Bay event holds the record for the highest wave run-up, other tsunamis are notable for their widespread devastation. The 2004 Indian Ocean tsunami, on December 26, 2004, was triggered by a magnitude 9.1 earthquake off Sumatra, Indonesia. This event generated waves up to 100 feet high near the epicenter, traveling across the Indian Ocean, affecting 14 countries, and causing an estimated 227,898 fatalities, making it one of the deadliest natural disasters in recorded history.
The 2011 Tohoku tsunami struck Japan on March 11, 2011. A magnitude 9.0 to 9.1 earthquake initiated this tsunami, with waves reaching heights of up to 133 feet along Japan’s Pacific coastline. The tsunami caused extensive damage, including the Fukushima nuclear disaster, and led to over 18,000 deaths and missing persons.
Historically, the 1883 Krakatoa eruption in Indonesia also generated tsunamis. On August 27, 1883, the volcanic collapse created waves that reached heights of up to 120 feet (37 meters) and resulted in approximately 36,000 deaths. These events underscore the diverse origins and varied impacts tsunamis can have globally.