Prehistoric tsunamis are tsunamis and so-called "megatsunamis" that occurred before recorded history. The events have been identified through oral tradition and/or geological evidence. Those events that have been identified through contemporary records are listed as historic tsunamis.
| Approx. date | Location | Cause | Evidence for tsunami |
| 66 million years BP | Chicxulub crater, Yucatan | asteroid strike | presumed [1] [2] |
| 35.5 million years BP | Chesapeake Bay | bolide impact | presumed [3] |
| 10,000 yrs BP | Seton Portage, British Columbia | landslide into lake | presumed [4] |
| 8,000 years BP | Mount Etna, Sicily | volcanic landslide | submarine sediments off Etna, submerged settlements off eastern Mediterranean coast, e.g. Atlit Yam [5] [6] |
| 8,000 years BP | Norwegian Sea | submarine landslip (Storegga Slide) | deposited sediments in Scotland [7] [8] |
| 5,500 BP | Northern Isles | tsunami (Garth tsunami) | deposits and contemporaneous mass burials [9] |
| 4,000 BP | Réunion island | landslide | presumed [10] |