Some waterfalls can be done by yourself

When it comes to creating waterfalls, some rivers opt for a "do-it-yourself" approach. A study published today in Nature suggests that for some rivers, the natural flow mechanisms of watercourses can form cascades without any external factors. The conditions that lead to these autogenic waterfalls could be common in mountain runoff streams and should be investigated further, the researchers said.

"Identifying autogenous waterfalls on the ground is pretty tricky," said Joel Scheingross, a geoscientist at the University of Nevada, Reno, who led the study. The team set up a reduced synthetic river in a laboratory to study autogenous waterfalls in isolation. "The experiments allowed us to control the type of rock, the evacuation of water, the sediments, etc., and to test the autogenic formation mechanism in the simplest possible scenario, without the additional complications that exist in nature, "he said.

DIY waterfall

Forced waterfalls from the outside can form when water flows from one type of rock to another, as glaciers retreat, landslides deviate a river or that tectonics suddenly changes the landscape, for example. Previous laboratory studies on waterfall formation simulated one or more of these factors, or used water-eroded materials alone without the presence of sediment.

In this study, Scheingross and his team set up a synthetic river bed made of polyurethane foam that mimics a uniform bedrock. They then poured water and sediment on its surface. They chose the parameters of the experiment to mimic mountain streams where waterfalls are common. The test lasted a little less than 4 hours, but when the model is developed, it represents 100,000 to 10,000 years of watercourse evolution.

The researchers found that the flow resulted in a series of repetitive steps in the bedrock, similar to past experiences. Some steps gradually migrated downstream, like a escalator, as the water eroded the rock from the edges of the steps.

Sometimes, however, a walk has built a gravel deposit that has protected it from rapid erosion. The floor beneath continued to spoil and finally became a stiff enough drop to form a free-flowing jet and a deep basin under water, an autogenous cascade. The team found that autogenic waterfalls tended to form a series along a river and that each fall lasted about 20 minutes (10 to 10,000 years in the wild).

The team is performing other tests to explore the range of conditions that can form an autogenous waterfall.

"If we can form autogenous waterfalls in many different experiments, we can also explore [whether] There is a morphological fingerprint of autogenous waterfalls, "said Scheingross, like the relationship between different walking heights.

Naturally formed, found in nature

Researchers have reported two areas of California likely to have autogenous waterfalls: the Sierra Madre Central Block of the San Gabriel Mountains and Bridalveil Creek in Yosemite. Both sites have a series of cascades, which has been predicted by this experiment.

The San Gabriel Mountain site is "intriguing," said Scheingross, because "erosion and uplift rates have been balanced over decades, so it's unlikely that tectonics can cause the development of waterfalls." 39; water. " The smaller falls upstream could be autogenic, he said.

This study is a "proof of concept," said Scheingross. "The hope is that once we can make a conclusive distinction between self-trained and forced cascades from the outside in nature, then we can begin to more critically assess how to use cascades and the knickzones to interpret the history of the Earth. "

-Kimberly Mr. S. Cartier (@AstroKimCartier), Editor

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