A study published in Nature today suggests that some waterfalls form from downhill movement. Given the role that waterfalls play in understanding the history of the Earth, these “self-forming” types could change the way we interpret it. In particular, waterfalls can act as signals for changes in tectonic activity, sea level, or climate change.
Before the new study, scientists believed that waterfall formation was the result of an external force acting on a river. These forces often stem from sea-level changes, earthquake-induced topography changes, and different erosion times across different rocks. But as National Geographic Reports, the new data reveals that waterfalls can form in the absence of an external force, which could change inferences that scientists have made about the Earth’s history through the study of waterfalls.
Researchers sometimes use Earth’s modern topography to infer things that have happened to it in the past. For example, select deep valleys in Yosemite Valley were used to determine the presence of glaciers in the past. There are many past events can lead to the formation of waterfalls, such as glaciers or landslides that shift topography and faults that cross rivers that move over time.
Most waterfalls tell a clear story about their origins—but for a rare few, it’s not obvious. Now, scientists have a new potential explanation for these mysterious cascades. https://t.co/JGlsHQJKZd
— News from Science (@NewsfromScience) March 13, 2019
As Gizmodo reports, the team of researchers behind the study created a laboratory model of a riverbed using a piece of polyurethane, which was designed to simulate the bedrock that acts as the foundation for waterfalls. Afterward, they angled it to a 10-degree angle and poured a mixture of water and gravel onto it to simulate sediment getting carried by the motion of a river.
At first, the water created a channel in the polyurethane, which lead to the formation of a staircase of pools after about 2.4 hours. After the pools, it built steep chutes — sloping channels that carried the water to lower levels — which resulted in more pools. Eventually, these pools led to the formation of a small waterfall. Even more interesting, the passage of time made way for erosion that deceased the waterfall behavior but led to the formation of a new one.
Although findings are still preliminary and have yet to be replicated outside of the laboratory, they suggest that we might have more to learn about waterfalls and the way that they can be used to interpret the Earth’s history.
“Waterfalls are these messengers of change on landscapes,” said Ben Crosby, a geomorphologist at Idaho State University who was not involved in the recent study.
“As an energetic point, they’re able to carry that message of change through watersheds. That’s why we give them so much attention as geomorphologists, and why taking pause at the attribution of that change is so important.”