Ship House, Russia

Some geologists believe that quite dramatic, unusually great flooding of rivers in the distant past might have influenced the legends. One of the latest, and quite controversial, hypotheses of this type is the Ryan-Pitman Theory, which argues for a catastrophic deluge about 5600 BC from the Mediterranean Sea into the Black Sea. This has been the subject of considerable discussion, and a news article from National Geographic News in February 2009 reported that the flooding might have been "quite mild".
There also has been speculation that a large tsunami in the Mediterranean Sea caused by the Thera eruption, dated about 1630–1600 BC geologically, was the historical basis for folklore that evolved into the Deucalion myth. Although the tsunami hit the South Aegean Sea and Crete it did not affect cities in the mainland of Greece, such as Mycenae, Athens, and Thebes, which continued to prosper, indicating that it had a local rather than a regionwide effect.
Another theory is that a meteor or comet crashed into the Indian Ocean around 3000–2800 BC, created the 30 kilometres (19 mi) undersea Burckle Crater, and generated a giant tsunami that flooded coastal lands.
It has been postulated that the deluge myth may be based on a sudden rise in sea levels caused by the rapid draining of prehistoric Lake Agassiz at the end of the last Ice Age, about 8,400 years ago.