Source Count: 14 | Weighted Score: 29 | Source Confidence: [3/5] | Primary Tier: 1 | Last Updated: April 10, 2026
Keywords: mega-tsunami, megatsunami, Lituya Bay, Storegga Slide, Canary Islands, volcanic flank collapse, wave runup, chevron dunes, coastal boulder deposits, submarine landslide
Category Tags: geological-events, tsunami, catastrophe, coastal, megaflood, volcanic, submarine-landslide
Cross-References: E_2_25 — Glacial Lake Outburst Floods · E_1_01 — Cataclysms Overview · E_2_01 — Volcanic Climate Events

QUICK SUMMARY

Mega-tsunamis — wave events with initial amplitudes of tens to hundreds of meters, far exceeding the 10–30 m waves generated by typical seismic tsunamis — are produced by catastrophic mechanisms including volcanic flank collapses, submarine landslides, asteroid impacts, and caldera collapses. While ordinary earthquake-generated tsunamis (such as the 2004 Indian Ocean tsunami and the 2011 Tōhoku tsunami) are devastating enough, the geological record preserves evidence of far larger events: the Lituya Bay megatsunami (Alaska, July 9, 1958) produced a wave runup of 524 m — the highest wave in recorded history — triggered by a rockslide into an enclosed fjord. The Storegga Slide (~8,200 years ago, offshore Norway) — a massive submarine landslide involving 3,500 km³ of sediment sliding along the Norwegian continental shelf margin — generated tsunamis up to 20–30 m that struck the coasts of Norway, Scotland, and the Shetland Islands, devastating Mesolithic coastal communities. Volcanic island flank collapses — massive lateral slides of volcano edifices into the ocean — are evidenced by enormous submarine debris fields: the Nuuanu Slide (Oahu, Hawaii, ~1.5 million years ago) moved ~5,000 km³ of material and likely generated waves hundreds of meters high across the Pacific basin. KEY FINDING The most debated modern mega-tsunami hazard is the potential collapse of the Cumbre Vieja volcano on La Palma, Canary Islands — proposed by Steven Ward and Simon Day (2001) as capable of generating a trans-Atlantic mega-tsunami reaching the U.S. East Coast with wave heights of 10–25 m. This scenario is highly contested: subsequent modeling by Gisler et al. (2006) and Abadie et al. (2012) significantly reduced the wave height estimates, and many volcanologists consider a rapid, large-scale collapse unlikely. The La Palma scenario illustrates the tension between worst-case geological hazard assessment and probabilistic risk analysis.

1. VERIFIED CLAIMS (Tier 1 — Peer-Reviewed / Established)

1.1 Lituya Bay, Alaska (1958)

• Date: July 9, 1958
• Trigger: A magnitude 7.8 earthquake on the Fairweather Fault caused a massive rockslide (~30.6 million m³ of rock and ice) from the cliffs above Gilbert Inlet into Lituya Bay, a T-shaped glacial fjord
• Wave runup: 524 m (1,720 ft) — the highest wave ever recorded, measured by the trimline (the line of destroyed forest) on the opposite slope of the inlet
• Two of three fishing boats in the bay survived by riding over the wave; the third was destroyed, killing two people (Ed and Mildred Swanson)
• Studied by Don Miller (USGS, 1960) and modeled by Fritz et al. (2009) at Oregon State University using a physical flume model — confirming that the initial wave reached the observed runup height

1.2 Storegga Slide (~8,200 years ago)

• One of the largest known submarine landslides: approximately 3,500 km³ of sediment slid along the Norwegian continental margin in three major events (Storegga Slide 1, 2, and 3 — the third, c. 8,200 BP, was the largest)
• Covered an area of ~95,000 km² — the slide scar is up to 290 km long, 160 km wide
• Generated tsunamis documented by:
• Sand deposits up to 4–6 m above contemporary sea level along the Norwegian coast
• Sand layers in coastal peat bogs on the Shetland Islands (up to 20–30+ m above sea level at some locations — amplified by coastal geometry) — documented by Dawson et al. (1988) and Bondevik et al. (2005)
• Tsunami deposits on the Scottish coast (northeastern Scotland), Faroe Islands, and Iceland
• The slide likely occurred due to destabilization of methane hydrates in continental shelf sediments as oceans warmed after the Last Glacial Maximum

1.3 Hawaiian Flank Collapses

• The Hawaiian Islands show evidence of at least 68 giant submarine landslides (identified by James Moore et al., 1989, 1994 using seafloor mapping):
• Nuuanu Slide (northeast of Oahu): ~5,000 km³ of material, ~230 km long — one of the largest landslides on Earth
• Wailau Slide (north of Molokai): ~1,500 km³
• Coral and marine sediment deposits at elevations of 60–326 m above current sea level on the islands of Lanai and Molokai have been interpreted (Moore and Moore, 1984) as evidence of mega-tsunami runup from these collapses, though this interpretation is debated (some attribute the deposits to tectonic uplift)
• Mega-tsunami modeling by Gary McMurtry et al. (2004) suggests flank collapses could generate initial wave heights of 100–300+ m near the source

1.4 Historical Volcanic Tsunamis

• Krakatoa (1883): Caldera collapse and pyroclastic flows entering the sea generated tsunamis up to ~40 m on the coasts of Java and Sumatra, killing ~36,000 people
• Anak Krakatau (December 22, 2018): A partial flank collapse generated a tsunami up to ~13 m, killing 437 people — demonstrating that volcanic tsunamis remain a present hazard

2. CREDIBLE CLAIMS (Tier 2 — Academic / Debated but Supported)

2.1 Cumbre Vieja/La Palma Scenario

• Ward and Day (2001) (Geophysical Research Letters) proposed that the western flank of Cumbre Vieja volcano (La Palma, Canary Islands) could collapse in a future eruption, sending ~500 km³ of rock into the Atlantic and generating a mega-tsunami:
• Near-field: Wave heights of 600–900 m at the source
• Far-field: Waves of 10–25 m striking the U.S. East Coast ~8 hours later
• The 2021 eruption of Cumbre Vieja (September 19 – December 13, 2021) did not cause a flank collapse
• Subsequent modeling has significantly reduced the threat estimates:
• Gisler et al. (2006): 3D modeling showed the slide would likely be slower and more fragmented than Ward-Day assumed, producing much smaller far-field waves (~1–3 m at the U.S. coast)
• Abadie et al. (2012): Confirmed that realistic source scenarios produce far-field waves of meters, not tens of meters
• Watt et al. (2019) (Geological Survey of Spain): Geological evidence suggests past Canary Island collapses occurred in multiple stages, not as single catastrophic events

2.2 Chicxulub Impact Tsunami

• The Chicxulub asteroid impact (66 million years ago, Yucatán) generated a mega-tsunami with estimated initial wave heights of 1,000+ m near the impact site:
• Range et al. (2022) (AGU Advances) used numerical simulation to model the global tsunami, estimating waves of 10–100+ m reaching coastlines worldwide, with evidence preserved in sediment deposits across the Gulf of Mexico, Caribbean, and Atlantic margins
• This is the largest tsunami event in the geological record but occurred before any human existence

3. SPECULATIVE CLAIMS (Tier 3 — Possible but Unverified)

3.1 Chevron Dune Deposits

• Dallas Abbott (Lamont-Doherty) and Ted Bryant (University of Wollongong) have identified large chevron-shaped sand deposits on coastlines in Madagascar, Australia, and elsewhere, interpreting them as evidence of mega-tsunami runup from oceanic asteroid impacts within the last ~10,000 years. This interpretation is contested — most coastal geomorphologists attribute chevron dunes to wind processes rather than tsunami deposits

3.2 Mediterranean Mega-Tsunamis

• Evidence for large tsunamis in the Mediterranean (beyond the well-documented Minoan/Thera event) includes deposits in eastern Sicily, Libya, and Egypt that researchers link to submarine landslides on the continental shelves of North Africa or to volcanic collapses on Etna or Stromboli. The evidence is preliminary

4. DUBIOUS CLAIMS (Tier 4 — No Credible Source / Contradicted by Evidence)

4.1 "Imminent La Palma Mega-Tsunami"

• DEBUNKED Media portrayals of the La Palma collapse as an imminent, civilization-threatening event are exaggerated. The Ward-Day worst case has been substantially revised downward by subsequent research. While the hazard is real in geological time, the probability of a single-event catastrophic collapse in any given century is extremely low

Counter-Arguments & Criticisms

Scale of Threat

The mega-tsunami hazard illustrates a fundamental problem in natural hazard assessment: events with very low probability but very high consequences are difficult to plan for. Volcanic flank collapses occur on timescales of tens of thousands to millions of years, making the per-century probability very small — but the consequences, if they occur, are enormous. Bill McGuire (Waking the Giant, 2012) has argued that climate change (ice sheet melting, sea-level rise, increased volcanic activity) may increase the frequency of these events, but this remains speculative.

IMAGES

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BIBLIOGRAPHY

1. Ward, Steven N.; Simon Day | 2001 | "Cumbre Vieja Volcano — Potential Collapse and Tsunami at La Palma, Canary Islands" | Geophysical Research Letters | ∅ | 28.17::3397–3400 | ∅ | ∅ | doi:10.1029/2001gl013110 | ∅ | ∅ | ∅
2. Fritz, Hermann M., Willi H | 2001 | "Lituya Bay Case: Rockslide Impact and Wave Run-Up" | Science of Tsunami Hazards | ∅ | 19.1::3–22 | Hager, and Hans-Erwin Minor | ∅ | doi:10.1007/978-3-0346-0064-4_9 | ∅ | ∅ | ∅
3. Miller, Don J | 1960 | "Giant Waves in Lituya Bay, Alaska" | USGS Professional Paper | ∅ | ∅ | 354-C : 51 86 | ∅ | doi:10.3133/pp354c | ∅ | ∅ | ∅
4. Bondevik, Stein, et al | 2005 | "The Storegga Slide Tsunami — Comparing Field Observations with Numerical Simulations" | Marine and Petroleum Geology | ∅ | 2::195–208 | 22.1 | ∅ | doi:10.1016/j.marpetgeo.2004.10.003 | ∅ | ∅ | ∅
5. Dawson, Alastair G., et al | 1988 | "Tsunami Sedimentation Associated with the Holocene Storegga Slide" | Journal of the Geological Society | ∅ | 145::129–141 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
6. Moore, James G., et al | 1989 | "Prodigious Submarine Landslides on the Hawaiian Ridge" | Journal of Geophysical Research | ∅ | ∅ | 94.B12 : 17465 17484 | ∅ | doi:10.1029/jb094ib12p17465 | ∅ | ∅ | ∅
7. McMurtry, Gary M., et al | 2004 | "Mega-Tsunami Deposits on Kohala Volcano, Hawaii, from a Flank Collapse of Mauna Loa" | Geology | ∅ | 32.9::741–744 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
8. Gisler, Galen, Robert Weaver; Michael Gittings | 2006 | "SAGE Calculations of the Tsunami Threat from La Palma" | Science of Tsunami Hazards | ∅ | 24.4::288–312 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
9. Abadie, Stéphane M., et al | 2012 | "Numerical Modeling of Tsunami Waves Generated by the Flank Collapse of the Cumbre Vieja Volcano (La Palma, Canary Islands)" | Journal of Geophysical Research | ∅ | ∅ | 117.C5 : C05030 | ∅ | ∅ | ∅ | ∅ | ∅
10. Range, Molly M., et al. e2021AV000627 | 2022 | "The Chicxulub Impact Produced a Powerful Global Tsunami" | AGU Advances | ∅ | 3.5:: | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
11. Paris, Raphaël, et al | 2007 | "Coastal Sedimentation Associated with the December 26, 2004 Tsunami in Lhok Nga, West Banda Aceh" | Marine Geology | ∅ | 4::93–106 | 238.1 | ∅ | ∅ | ∅ | ∅ | ∅
12. McGuire, Bill | 2012 | ∅ | Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes | ∅ | ∅ | Oxford: Oxford University Press | ∅ | ∅ | ∅ | ∅ | ∅
13. Watt, Sebastian F | 2019 | "From Catastrophic Collapse to Multi-Phase Deposition: Flow Transformation, Seafloor Interaction and Triggered Eruption Following a Volcanic-Island Landslide" | Earth and Planetary Science Letters | ∅ | 517::135–147 | L., et al | ∅ | ∅ | ∅ | ∅ | ∅
14. Bryant, Edward | 2014 | ∅ | Tsunami: The Underrated Hazard | ∅ | ∅ | Berlin: Springer | 3rd | ∅ | ∅ | ∅ | ∅

CROSS-REFERENCE INDEX

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