A tsunami is a series of waves generated by the sudden displacement of a massive volume of water, typically in the ocean. Defining the “largest” tsunami is complicated because the term can refer to the maximum wave height reached on land or the overall scale of destruction and trans-oceanic reach. This article explores both definitions to provide a comprehensive answer to what constitutes the largest tsunami in recorded history.
Defining “Largest”: How Tsunami Size is Measured
Scientists use distinct metrics to quantify the power of a tsunami. The most common measurement is run-up, which is the maximum vertical height the water reaches above sea level on the shore. Run-up defines the highest-recorded wave, as it measures the water’s inland penetration and height.
In the deep ocean, tsunami wave height is often less than a meter and is measured by specialized sensors. The Moment Magnitude Scale (\(M_w\)) quantifies the energy of the underlying earthquake that often triggers a tsunami. This seismic measurement is sometimes correlated with the Tsunami Magnitude Scale (\(M_t\)), which uses instrumental wave amplitudes measured by tide gauges. A high \(M_w\) indicates a powerful tectonic event and a greater potential for widespread destruction across an ocean basin.
The Record Holder: The 1958 Lituya Bay Megatsunami
The definitive record for the highest tsunami wave ever measured belongs to the event that occurred in Lituya Bay, Alaska, on July 9, 1958. This event was not a typical tectonic tsunami but a localized megatsunami, a specific class of wave generated by a sudden, massive impact into the water. A powerful magnitude 7.8 to 8.3 earthquake on the nearby Fairweather Fault triggered the collapse of an estimated 30 million cubic meters of rock and glacial ice.
This enormous landslide plunged into the narrow Gilbert Inlet at the head of the bay, creating an immense splash effect. The resulting wave surged up the steep slope opposite the rockfall, washing out trees and vegetation to an astonishing run-up height of 1,720 feet (524 meters), which remains the highest ever documented. Because the wave was generated by a rockfall and not a plate displacement, its energy was focused within the confines of the fjord. The sheer height of this water surge makes the Lituya Bay event the physical record holder for the world’s largest tsunami wave.
Catastrophic Scale: Tsunamis Defined by Global Impact
While the Lituya Bay wave was the highest, the most destructive and globally significant event was the 2004 Indian Ocean Tsunami. This tsunami was triggered by the Sumatra-Andaman earthquake, a colossal undersea megathrust event with a magnitude estimated between \(M_w\) 9.1 and 9.3. The earthquake occurred along a subduction zone, where the Indian Plate is forced beneath the Burma Plate.
The resulting vertical displacement of the seafloor across a rupture zone of over 1,300 kilometers transferred immense energy to the entire water column. This mechanism created a trans-oceanic tsunami that propagated across the Indian Ocean basin, affecting coastlines in fourteen countries. The waves reached heights of up to 100 feet (30 meters) in some areas, particularly near the epicenter in Sumatra. The devastation and lack of an existing warning system led to a staggering loss of life, with the final death toll estimated at approximately 228,000 people. This event, along with others like the \(M_w\) 9.1 TÅhoku earthquake and tsunami in Japan in 2011, represents the largest tsunamis in terms of energy release and widespread devastation.
Primary Geological Causes of Mega-Tsunamis
The primary mechanisms of tsunami generation are seismic and non-seismic. The most common cause for trans-oceanic tsunamis is seismic activity, specifically large-magnitude earthquakes occurring in subduction zones. The sudden, vertical movement of the seafloor along a fault boundary displaces the entire water column, generating waves that can travel thousands of miles.
Non-seismic causes are responsible for the highest-reaching but typically more localized megatsunamis. These are generated by sudden, massive displacements of material into the water, such as the coastal and underwater landslides that caused the Lituya Bay event. Other non-seismic triggers include massive volcanic eruptions or flank collapses, such as the 1883 Krakatoa eruption. In extremely rare instances, a large meteor impact could also displace a sufficient volume of water to create a global-scale megatsunami.