Waterfalls are furious cascades of water, sometimes scoring the landscapes in which they flow as they obey gravity’s demands.
There is a longstanding assumption that they can only form when permitted by other natural forces. But this paradigm may be about to change. By building a scaled-down river in their laboratory, a team of researchers demonstrated that waterfalls can sometimes bring themselves into existence without any outside help. By better understanding how waterfalls can form, the new study may prompt scientists to reconsider how our planet shaped itself.
Although there had been suggestions in the scientific literature that waterfalls could self-form, it wasn’t clear how that could occur. This new evidence, said Edwin Baynes of the University of Auckland , provides a “very convincing” explanation.
To investigate how waterfalls form, researchers built a 26-foot long, 12-inch wide, 3.3-foot deep channel. They filled it with a foamy bedrock, tilted it at a 20% slope and let sediment-rich water flow down its surface. By using a riverbed made of foam rather than real rock, the team were able to watch millenniums of erosion play out under very short time scales.
The turbulent flow of the “river” down a steep slope started digging out parts of the riverbed. Eventually, with no externally triggered changes to the sediment load, the flow rate, the underlying channel shape, a deep pocket of erosion formed, one that made the river jet off from the higher section of the riverbed and splash down some distance away. A waterfall appeared, all by itself.
The research could contribute to our understanding of Earth’s landscapes. By incorrectly attributing the formation of waterfalls to external forces, scientists may be “picking out erroneous climatic or tectonic signals,” said Kate Learyfrom the University of California .
The results suggest that the steep, upstream sections of rivers in mountain ranges may be particularly likely to feature self-forming waterfalls. If so, the geological histories of some of these elevated realms need to be re-examined.