This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint.
Deglacial Mass-Movement Floods as a Potential Source of Catastrophic Flood Traditions: A Testable Geomythological Hypothesis
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Authors
Tomoyasu Morita 
Abstract
Catastrophic flood traditions occur in many geographically separated cultures, but their possible geological substrates need not be uniform. Existing explanations include river floods, earthquake and volcanic tsunamis, glacial-lake outburst floods, postglacial sea-level rise, and cultural transmission. This paper proposes a complementary, explicitly testable hypothesis: during the terminal Pleistocene and early Holocene, deglaciation and associated paraglacial adjustment increased opportunities for catastrophic glacier, ice-rock, and rock-slope failures in many formerly glaciated mountain regions; where such failures entered lakes, fjords, or confined river valleys, they could generate extreme displacement waves, debris-rich floods, secondary damming and outburst floods, and long-lived burial or destruction of valley-floor habitat. Modern analogues demonstrate the required magnitudes. The 2015 Taan Fiord landslide generated 193 m run-up, while the 2020 Elliot Creek rock avalanche produced greater than 100 m run-up before evolving into a destructive outburst flood. A 2026 glacier-associated slope failure in Nepal generated a debris-laden flood that travelled about 100 km, illustrating the continuing relevance of this hazard class, although its detailed mechanism remains under study. Geomythological and ethnographic evidence shows that mass-movement-generated floods can enter cultural memory: a Tlingit account recorded in 1909 explicitly describes an avalanche entering a lake, forcing water out, and overwhelming a settlement. The proposed Deglacial Mass-Movement Flood Tradition (DMFT) hypothesis therefore predicts a non-random association between formerly glaciated mountain settings and narrative features such as sudden onset, extreme local run-up, debris transport, anomalous flow direction, high-ground survival, and permanent loss of inhabited land. The hypothesis is not a claim of a simultaneous worldwide flood. It is a framework for testing whether regionally asynchronous but climatically clustered catastrophic events contributed to a subset of extraordinary flood traditions.
DOI
https://doi.org/10.31223/X53502
Subjects
Earth Sciences, Geology, Geomorphology, Glaciology, Hydrology
Keywords
deglaciation, paraglacial, rock avalanche, ice-rock avalanche, landslide tsunami, debris flood, geomythology, oral tradition, flood tradition, Holocene
Dates
Published: 2026-09-05 13:48
Last Updated: 2026-09-05 13:48
License
CC BY Attribution 4.0 International
Additional Metadata
Conflict of interest statement:
None.
Data Availability:
No new datasets were generated or analyzed for this hypothesis and scoping-review manuscript. All evidence discussed in this preprint is derived from publicly available published literature and sources cited in the manuscript.
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Comment #339 Tomoyasu Morita @ 2026-09-05 23:50
As the author, I thought it might be fun to compare a few details of the Noah tradition with what a catastrophic rock–ice avalanche and debris-flood cascade might actually look like to an ancient observer, using the 2026 Nepal disaster as a modern analogue.
* **Advance warning before the catastrophe**
In the 2026 Nepal event, the glacier–rock mass showed signs of instability before failure, including visible cracking, unusual meltwater conditions, and accelerating movement. An ancient community familiar with its valley might interpret such signs as a warning that “the mountain was behaving strangely.”
* **The Ark may not need to be imagined as a conventional ship**
Genesis describes a large enclosed structure but gives no sail, rudder, or propulsion system. In modern avalanche engineering, wedge-shaped protection structures are pointed toward an incoming avalanche so that the moving mass is split and deflected around a protected space. A robust box-like or wedge-protected shelter could therefore be an interesting physical analogy for survival in a debris-rich flood, even if the later tradition remembered it as a floating Ark.
* **Survival on high ground**
The 2026 Nepal disaster showed how an ice–rock collapse can transform an entire valley into a debris corridor. Even after the main flood passes, thick deposits of mud, rock, and sediment can make former settlements unusable for years or permanently.
* **“The whole world” destroyed**
In Nepal, multiple settlements and infrastructure along the same river corridor were overwhelmed. For a small ancient population living entirely within one valley system, the destruction of every known village, field, road, and crossing could reasonably be remembered as the destruction of their entire world.
* **Water appearing to rise above mountains**
This need not mean that regional water level literally exceeded major mountain summits. If settlements upstream, downstream, and beyond intervening ridges were all destroyed, survivors could conclude that the flood had passed over or beyond the mountains. Extreme local run-up, combined with debris deposition high on valley sides, would reinforce that impression.
* **Water behaving unlike an ordinary river flood**
The 2026 Nepal event was not simply a river rising after rain. It involved a fast-moving mixture of water, mud, boulders, ice, and other debris generated by a catastrophic slope failure. Such flows can reach extreme local elevations and can propagate in unexpected directions, including temporarily upstream into tributary valleys.
None of this demonstrates that Noah’s Ark records a deglacial glacier- or rock-slope-collapse event. But the 2026 Nepal disaster gives us a useful modern reference point: some details that sound mythological when imagined as an ordinary flood may look much less extraordinary when compared with a real mass-movement flood cascade.