The cascades are furious waterfalls of water, sometimes marking the landscapes in which they flow while respecting the requirements of gravity. From the glittering Skógafoss of Iceland to the family of the Falls of Milford Bay, New Zealand, they are aquatic and zealous showcases of the natural world.
Powerful, although waterfalls may appear, there has long been a hypothesis that they can only be formed if other natural forces permit. The tectonic movement that displaces rocks, changes in sea level, the passage of a resilient rock to a more easily erodible rock are all factors by which external forces are thought to influence the formation of cascades.
But this paradigm is about to change. By building a small river in their laboratory, a team of researchers demonstrated that cascades can sometimes be created without any outside help.
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Scientists "often use the presence of waterfalls to try to reconstruct the story of a landscape," said Edwin Baynes, a quantitative geomorphologist at the University of Auckland in New York. New Zealand, who did not participate in the study. By better understanding how waterfalls can form, the new study can prompt scientists to reconsider how our planet has been shaped and help them to go back in geological time with greater precision.
Although the scientific literature suggested that waterfalls could form themselves, it was unclear how this could happen. According to Dr. Baynes, this new experimental evidence provides a "very convincing" explanation.
In order to study how the cascades are formed, the researchers built a channel 26 feet long, 12 inches wide and 3.3 feet deep. They filled it with a sparkling bedrock, tilted it to a 20 slope and allow the sediment-rich water to flow on its surface. Using a riverbed made of moss rather than real rock, the team was able to observe millennia of erosion unfold in a very short time.
The turbulent flow of the "river" on a steep slope began to dig portions of the riverbed. The situation was so uneven, with some pockets eroding faster than others, and uneven erosion magnified as the river continued to flow rapidly. Finally, without external modification of the sediment load, flow, shape of the underlying channel or anything else, a deep erosion pocket is formed. a way.
A waterfall appeared, all alone.
Scientists had assumed that waterfalls always resulted from geological or climatic changes. "Now, I think we're starting to question that idea," he said. Joel Scheingross, assistant professor of geoscience at the University of Nevada in Reno, and senior author of the study, published Wednesday in Nature.
Research could contribute to our understanding of the Earth's landscapes. By mistakenly assigning the formation of waterfalls to external forces, scientists could "detect false climate or tectonic signals," said Kate Leary, a fluvial geomorphologist at the University of California at Santa Barbara who was not part of the study. "Developing a way to discern self-formed cascades from the outside would be very beneficial in eliminating these signals in tectonically active landscapes."
The results of these experiments suggest that the steepsections upstream of rivers in mountain ranges around the world are particularly likely to have self-forming cascades. If this is the case, it is necessary to re-examine the geological history of some of these high realms.
Mr. Scheingross said that further research is needed to strengthen his team's model. But if their hypothesis is supported by additional evidence, then the genesis of the cascades "is a more complicated picture than we originally thought," he said.