Megatsunami

A megatsunami is an exceptionally large tsunami, usually generated by a massive landslide, volcanic collapse, or impact. Its waves can reach extreme heights near the source and diminish rapidly with distance.

Landslide tsunami: A tsunami generated when a landslide rapidly displaces water. Rapid slope failure is the most common proposed trigger for megatsunamis.
Lituya Bay megatsunami: A 1958 wave in Alaska's Lituya Bay, triggered by an earthquake-induced rockslide. Its roughly 524-meter run-up is the best-known modern megatsunami measurement.
Earthquake tsunami: A tsunami generated by sudden seafloor movement during an earthquake. Earthquake tsunamis commonly affect broad ocean basins rather than producing only extreme near-source heights.
Lituya Bay: A narrow inlet in southeastern Alaska bordered by steep mountain slopes. Its confined shape amplified the effects of the 1958 rockslide-generated wave.
Volcanic flank collapse: The gravitational failure of part or all of a volcano's side. A collapsing volcanic flank can displace enormous volumes of water.
Storegga Slide: A massive prehistoric submarine landslide off Norway that generated tsunamis around the North Atlantic. Its deposits provide evidence for a major landslide-generated tsunami, though not an extreme local run-up.
Storm surge: An abnormal rise in coastal water level caused primarily by a storm's winds and pressure. Storm surges raise coastal water but are not sudden, wave-train events like megatsunamis.
Don J. Miller: An American geologist who studied the 1958 Lituya Bay wave and its deposits. Miller documented the event's extreme run-up and helped establish its scientific record.
Impact tsunami: A tsunami produced when an asteroid or other body strikes a body of water. A sufficiently large impact can generate exceptionally high waves near the strike.
Surtsey: A volcanic island formed off Iceland during an eruption that began in 1963. Its eruptions illustrate how volcanic activity can generate local waves without proving megatsunami scale.

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Chicxulub impactRelated: The impact displaced ocean water and generated enormous waves around the Gulf of Mexico.