# Megatsunami
A megatsunami is an unusually large tsunami, generally defined by an initial wave height or amplitude at its source exceeding 100 m or 50 m respectively, produced by mechanisms such as large landslides, volcanic flank collapses, or asteroid impacts rather than by ordinary earthquake fault rupture. No unambiguous, widely accepted definition of the term exists; it has been applied variously to wave height, run-up height, geographic extent, and overall impact[1](https://www.sciencedirect.com/science/article/abs/pii/S0025322714000759).
| Key fact | Detail |
|---|---|
| Proposed definition | Initial wave height/amplitude at source exceeding 100 m/50 m (Goff et al., 2014); under this definition mega-tsunamis can only arise from large bolide impacts, violent volcanic activity, oceanic island flank collapse, or possibly extreme tsunamigenic submarine earthquakes[1](https://www.sciencedirect.com/science/article/abs/pii/S0025322714000759) |
| Capable sources | Among all tsunami source mechanisms, only large landslides and asteroid impacts have the potential to generate mega-tsunamis[2](https://doi.org/10.1016/j.earscirev.2020.103381) |
| Highest recorded run-up | 524 m at Lituya Bay, Alaska, on 10 July 1958 (Miller, 1960); a later USGS summary gives a peak runup of 530 m (~1,740 ft)[3](https://pubs.usgs.gov/pp/0354c/report.pdf) • [4](https://www.usgs.gov/programs/landslide-hazards/science/2025-tracy-arm-landslide-generated-tsunami) |
| Second-highest recorded | 481 m run-up in Tracy Arm fjord, Alaska, on 10 August 2025, from a landslide of roughly 60 to 100 million cubic meters[5](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds) • [4](https://www.usgs.gov/programs/landslide-hazards/science/2025-tracy-arm-landslide-generated-tsunami) |
| Largest known source | The Storegga landslide offshore Norway, about 3,200 km³, the only documented landslide-tsunami source exceeding 10 billion m³ in volume12 • [6](https://link.springer.com/article/10.1007/s11069-025-07551-2) |
| Deadliest landslide tsunami | The 1792 flank collapse of Mt. Mayuyama, Japan, into Ariake Bay produced 20 m run-up and killed about 10,000 people[6](https://link.springer.com/article/10.1007/s11069-025-07551-2) |
| Historical example count | Under the Goff et al. definition, the 1958 Lituya Bay tsunami could be considered the only historical example of a mega-tsunami[2](https://doi.org/10.1016/j.earscirev.2020.103381) |
## Definition and use of the term
The term megatsunami emerged in scientific literature around 1990, linked to giant waves hypothesized for the asteroid impact at the [Cretaceous–Paleogene boundary](https://www.edgepedia.org/cretaceous-paleogene-boundary) in the [Gulf of Mexico](https://www.edgepedia.org/gulf-of-mexico); earlier work on that event had referred to wave heights of 50 to 100 m as a "very large tsunami"[7](https://www.mdpi.com/2624-795X/5/3/48). Because no threshold has been agreed on, and because researchers disagree over whether height should be measured at the shore or at the source, the word has been used in a rather arbitrary fashion across the literature[1](https://www.sciencedirect.com/science/article/abs/pii/S0025322714000759) • [7](https://www.mdpi.com/2624-795X/5/3/48).
James Goff, James P. Terry, Catherine Chagué-Goff, and Kazuhisa Goto, tsunami researchers then at the [University of New South Wales](https://www.edgepedia.org/university-of-new-south-wales) and related institutions, proposed in *Marine Geology* in 2014 a stricter definition based solely on the initial wave height or amplitude at the source, exceeding 100 m or 50 m respectively. A source-based definition avoids complications from coastal configuration, bathymetry, and geomorphology at affected locations[1](https://www.sciencedirect.com/science/article/abs/pii/S0025322714000759). Under this definition, mega-tsunamis are restricted to rare events on geological timescales, and all tsunamis generated by historical earthquakes are excluded[2](https://doi.org/10.1016/j.earscirev.2020.103381). A review of the geological record concluded that with a maximum run-up of 524 m, the 1958 [Lituya Bay](https://www.edgepedia.org/lituya-bay) tsunami could be considered the only historical example[2](https://doi.org/10.1016/j.earscirev.2020.103381).
The definition matters for classification. The 2018 Anak Krakatau tsunami could enter the mega-tsunami category under a source-based rule, but wave heights on the coasts of Sumatra and Java, 40 to 60 km from the volcano, were lower than 7 m[2](https://doi.org/10.1016/j.earscirev.2020.103381). Geologists generally do not call the 2004 Indian Ocean or 2011 Tohoku-oki tsunamis mega-tsunamis, since far larger events are known from the geological record[2](https://doi.org/10.1016/j.earscirev.2020.103381).
## Sources and mechanisms
Most tsunamis are generated by earthquakes, but the largest waves come from other mechanisms. Only large landslides and asteroid impacts have the potential to generate mega-tsunamis[2](https://doi.org/10.1016/j.earscirev.2020.103381). Landslide sources are classified as subaerial, partially submerged, or completely submerged, depending on the initial position of the landslide[8](https://www.intechopen.com/chapters/73416). In a database of 297 documented landslide-triggered tsunamis, 47% came from subaerial landslides, 37% from submarine ones, and 16% from partially submerged ones; most were triggered by earthquakes (44% of cases), with volcanic landslides accounting for about 8% and paraglacial conditions, the slope-instability processes that follow deglaciation, for 11%[6](https://link.springer.com/article/10.1007/s11069-025-07551-2).
The physics of generation differs sharply between settings. The ratio between landslide velocity and tsunami wave speed, the [Froude number](https://www.edgepedia.org/froude-number) \( Fr = u/\sqrt{gd} \), where \( u \) is landslide velocity, \( d \) water depth, and \( g \) gravitational acceleration, measures the degree of criticality of the coupling[17](https://www.nature.com/articles/s41467-026-78272-8). For submarine landslides, wave generation is most efficient when \( Fr = 1 \), when the landslide and the tsunami travel at the same speed; subaerial impacts instead scale non-linearly with the product of Froude number and frontal slide area[9](https://link.springer.com/article/10.1007/s10346-020-01429-z). Subaerial landslides often involve large Froude numbers and strong nonlinearities, while fully submerged slides generate waves through a different coupling[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC4608034/).
Volume alone does not determine wave height. Landslides with the highest volumes do not necessarily trigger the highest waves: giant and monster landslides (over 10 billion m³)9 produced tsunamis with maximum water heights on the order of tens of meters, while the highest waves were triggered by large landslides in confined settings. Most waves above 100 m were generated by subaerial hard-rock landslides in inland waters or enclosed marine environments, where energy dissipates slowly and reflection amplifies the waves[6](https://link.springer.com/article/10.1007/s11069-025-07551-2).
## Lituya Bay, 1958
The 1958 event remains the benchmark. On 10 July 1958, an earthquake of magnitude 7.8 to 8.3 on the Fairweather fault triggered a rockslide of roughly 30 million cubic meters into Gilbert Inlet at the head of Lituya Bay, Alaska[3](https://pubs.usgs.gov/pp/0354c/report.pdf) • [11](https://doi.org/10.1007/s00024-008-0435-4). The landslide impacted the water at high speed and produced the highest wave run-up in recorded history: water cleared the forest to 524 m on the opposite slope, and a wave of about 30 m passed beyond the bay[3](https://pubs.usgs.gov/pp/0354c/report.pdf). The run-up is not the wave height in the water; researchers distinguish the local run-up of 524 to 525 m from a maximum wave height on the bay's slopes of about 150 m and a maximum wave amplitude of about 50 m[7](https://www.mdpi.com/2624-795X/5/3/48).
The bay's geometry amplified the waves. Its narrow shape and U-shaped seafloor caused the water to slosh back and forth, and the steep walls and proximity to an active fault mean further events are expected; one scientist calculated giant waves occur there roughly once every quarter century[12](https://science.nasa.gov/earth/earth-observatory/lituya-bays-apocalyptic-wave-147557/). Lituya Bay had documented landslide tsunamis in 1853, 1874, 1900, 1936, and 1958, and the 1958 trimline of destroyed forest remains visible in satellite imagery[6](https://link.springer.com/article/10.1007/s11069-025-07551-2) • [12](https://science.nasa.gov/earth/earth-observatory/lituya-bays-apocalyptic-wave-147557/). The event was later reproduced in a three-dimensional physical model at 1:400 scale, whose measured amplitudes serve as a benchmark for analytical and numerical models[11](https://doi.org/10.1007/s00024-008-0435-4).
## Other notable events
Confined water bodies dominate the record of extreme run-ups. The highest wave measured in inland waters was 260 m at Vajont, Italy, in 1963, when a landslide entered a reservoir; the highest in an open marine environment was 42 m during the 1946 Aleutian tsunami[6](https://link.springer.com/article/10.1007/s11069-025-07551-2). The deadliest landslide tsunami came from a volcanic flank: in 1792 the flank of Mt. Mayuyama in Kyushu, Japan, collapsed into Ariake Bay during a period of volcanic activity, generating waves with a maximum run-up of 20 m and killing about 10,000 people[6](https://link.springer.com/article/10.1007/s11069-025-07551-2).
Submarine landslides entered mainstream hazard thinking after 1998, when a seabed slump offshore of northern [Papua New Guinea](https://www.edgepedia.org/papua-new-guinea) generated a tsunami up to 15 m high that killed more than 2,200 people. The event demonstrated the importance of seabed mapping and stimulated new numerical modeling methods[13](https://www.annualreviews.org/content/journals/10.1146/annurev-earth-063016-015810). In the prehistoric record, the Storegga landslide offshore Norway, with a volume of about 3,200 km³, generated tsunami waves whose deposits remain visible along the coasts of the entire [North Sea](https://www.edgepedia.org/north-sea) and northern [Atlantic Ocean](https://www.edgepedia.org/atlantic-ocean)[6](https://link.springer.com/article/10.1007/s11069-025-07551-2).
## Tracy Arm, 2025
The second-highest run-up ever recorded occurred on 10 August 2025, when a landslide dropped roughly 60 million cubic meters of rock (preliminary USGS estimates run up to about 100 million cubic meters) into Tracy Arm fjord south of [Juneau, Alaska](https://www.edgepedia.org/juneau-alaska). The tsunami reached 481 m (1,578 ft) up the fjord slopes, higher than the roof of [One World Trade Center](https://www.edgepedia.org/one-world-trade-center), and no boats were caught despite the fjord being heavily visited by cruise ships[5](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds) • [4](https://www.usgs.gov/programs/landslide-hazards/science/2025-tracy-arm-landslide-generated-tsunami) • [14](https://doi.org/10.1126/science.aec3187).
Researchers led by Thomas Monahan, a senior research associate in engineering at the [University of Oxford](https://www.edgepedia.org/university-of-oxford), reconstructed the event from satellite imagery and seismic data. The wave began as an initial 100-m-high breaking wave traveling at more than 70 meters per second, then formed a standing wave, or seiche, that sloshed in the narrow fjord for over a day; only the second time such a seiche had been recorded, after one in [Greenland](https://www.edgepedia.org/greenland) in 2023[5](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds) • [14](https://doi.org/10.1126/science.aec3187). Small, local, repeating earthquakes increased in rate in the days to hours before the landslide, a precursory signal that co-author Stephen Hicks, an Earth scientist at [University College London](https://www.edgepedia.org/university-college-london), suggested could be developed into a warning system[5](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds). The fjord is the outlet of the South Sawyer Glacier, which had been retreating rapidly, and researchers have linked glacier retreat to slope destabilization in high-latitude settings[5](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds).
## Study and modeling
Landslide tsunamis are studied with theoretical analysis, physical model experiments, and numerical simulation[15](https://www.mdpi.com/2073-4441/15/10/1879). Laboratory experiments with rigid and granular landslide models have produced empirical equations for wave amplitude, height, and period as functions of landslide Froude number, relative mass, thickness, and slope angle[8](https://www.intechopen.com/chapters/73416). Numerically, models based on the [Navier–Stokes equations](https://www.edgepedia.org/navier-stokes-equations), including volume-of-fluid computational fluid dynamics, are considered necessary to resolve the momentum exchange between landslide and water during generation, while Boussinesq-type and shallow-water equations handle propagation and run-up over larger domains[8](https://www.intechopen.com/chapters/73416) • [16](https://nhess.copernicus.org/articles/3/391/2003/nhess-3-391-2003.pdf).
Uncertainty is a central problem. Because landslide dynamics are rarely observed directly, probabilistic inversion of landslide deposits and tsunami run-up data is used to constrain source parameters; even for a well-documented event, uncertainty bounds can be large, and ensemble simulations of a hypothetical Rockall Bank landslide produced surface elevations ranging from 5 to 25 m at a coastal point for 100 random realizations[9](https://link.springer.com/article/10.1007/s10346-020-01429-z). The 2014 Lake Askja landslide tsunami in Iceland, with run-ups of 10 to 80 m thoroughly sampled around the lake, is viewed as among the best-documented historical landslide tsunamis and a benchmark for testing such models[9](https://link.springer.com/article/10.1007/s10346-020-01429-z).
## References
1. [James Goff, James P. Terry, Catherine Chagué-Goff, Kazuhisa Goto (2014). What is a mega-tsunami? Marine Geology 358, 12–17.](https://www.sciencedirect.com/science/article/abs/pii/S0025322714000759)
2. [Advances in the study of mega-tsunamis in the geological record. Earth-Science Reviews (2020).](https://doi.org/10.1016/j.earscirev.2020.103381)
3. [Don J. Miller (1960). Giant waves in Lituya Bay, Alaska. U.S. Geological Survey Professional Paper 354-C.](https://pubs.usgs.gov/pp/0354c/report.pdf)
4. [2025 Tracy Arm Landslide-Generated Tsunami. U.S. Geological Survey Landslide Hazards Program.](https://www.usgs.gov/programs/landslide-hazards/science/2025-tracy-arm-landslide-generated-tsunami)
5. [A 2025 Alaskan tsunami was one of the largest on record, new research finds. Live Science.](https://www.livescience.com/planet-earth/a-2025-alaskan-tsunami-was-one-of-the-largest-on-record-new-research-finds)
6. [Landslide-triggered tsunamis – a review. Natural Hazards (Springer).](https://link.springer.com/article/10.1007/s11069-025-07551-2)
7. [Global Historical Megatsunamis Catalog (GHMCat). Data (MDPI).](https://www.mdpi.com/2624-795X/5/3/48)
8. [Alessandro Romano. Physical and Numerical Modeling of Landslide-Generated Tsunamis: A Review. IntechOpen.](https://www.intechopen.com/chapters/73416)
9. [On the landslide tsunami uncertainty and hazard. Landslides (Springer).](https://link.springer.com/article/10.1007/s10346-020-01429-z)
10. [On the characteristics of landslide tsunamis. Philosophical Transactions of the Royal Society A (PMC).](https://pmc.ncbi.nlm.nih.gov/articles/PMC4608034/)
11. [Lituya Bay Landslide Impact Generated Mega-Tsunami 50th Anniversary. Pure and Applied Geophysics (2009).](https://doi.org/10.1007/s00024-008-0435-4)
12. [Lituya Bay's Apocalyptic Wave. NASA Earth Observatory (2020).](https://science.nasa.gov/earth/earth-observatory/lituya-bays-apocalyptic-wave-147557/)
13. [Submarine Landslides and Their Tsunami Hazard. Annual Review of Earth and Planetary Sciences.](https://www.annualreviews.org/content/journals/10.1146/annurev-earth-063016-015810)
14. [A 481-meter-high landslide-tsunami in a cruise ship–frequented Alaska fjord. Science (2026).](https://doi.org/10.1126/science.aec3187)
15. [A Review of Research Methods and Evolution Mechanisms of Landslide-Induced Tsunamis. Water (MDPI).](https://www.mdpi.com/2073-4441/15/10/1879)
16. [P. Watts et al. Landslide tsunami case studies. Natural Hazards and Earth System Sciences 3, 391 (2003).](https://nhess.copernicus.org/articles/3/391/2003/nhess-3-391-2003.pdf)
17. [Human-enhanced tsunami hazard in large lakes, Nature Communications](https://www.nature.com/articles/s41467-026-78272-8)
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*Topic: Encyclopedia › Physical world and mathematics › Earth sciences › Hydrology and ocean science › Oceanography › Physical oceanography and circulation › Tides, waves, and sea level*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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