Long after a river has dried up, its belt of canals endures.
Made up of strips of sediment surrounding the river, the channel belts, once hardened into rock, preserve the river paths of old. However, reconstructing details of an ancient river from canal belt deposits is a notoriously difficult task.
New research by scientists at the University of Texas at Austin is making progress on this front. Lead author Tian Dong, a postdoctoral researcher at UT Jackson School of Geosciences, said that by analyzing modern rivers, they were able to come up with a rule that relates channel belts to river patterns, finding that ‘in general, the more channels there are. river a, the narrower its channel belt.
Since the physics that shape rivers are the same across time and space, the rule should also apply to ancient rivers and rivers on other planets, according to co-author Timothy Goudge, an assistant professor at the Jackson School.
“We can look at a river deposit from 100 million years ago on Earth or 3.5 billion years ago on Mars and we can say something about what the actual river was like,” did he declare.
The results were published June 13 in the journal Geology.
In addition to helping scientists visualize ancient rivers, the ruler can also help them interpret how those rivers influenced the larger landscape. Rivers with narrower channel belts can more easily access the surrounding floodplain – which shapes how landscapes are built and materials are deposited downstream.
“For multi-channel systems, such as braided rivers, they’re actually in a very narrow channel belt, so they’re very close to the floodplain,” Dong said. “So there is potentially more interaction between the river and the floodplain material.”
The rule has some caveats. This does not apply to confined rivers which are prevented from migrating freely by their surrounding landscape. But when rivers are free to move and meander through the country, there is a direct link between an increasing number of river channels and a shrinking canal belt. Scientists have also discovered that as the belt shrinks, it also becomes smoother with less sharp edges.
The researchers discovered the rule by analyzing 30 modern rivers and their channel belts, using high-resolution imagery and elevation data captured by satellites. Dong said he had a hunch about the connection, noticing a pattern between the channel of the river and the width of the channel belt while scrolling on Google Earth. But he wasn’t sure if his intuition would turn out to be correct once the data was calculated.
“No one had really systematically looked at the relationship between the planforms of rivers and channel belts, so we didn’t really know what we were expecting,” Dong said.
In addition to having narrower canal belts, research has also found that multi-channel rivers take up more space on the canal belt, occupying 50% or more of the canal belt area. In contrast, single-channel systems, such as meandering rivers, consume only 1%. This further enhances the ability of multi-channel rivers to pick up and move sediment, Dong said. Since the organic matter of plants and animals is part of these sediments, this means that multichannel rivers may not store organic carbon in their floodplains as long before transporting it to the ocean, where it can affect the marine life.
Channel belts are a common feature on Mars, reminiscent of the Red Planet’s wetter past. They are also likely found on Saturn’s moon Titan, where rivers of liquid methane have been identified by space probes.
Goudge and Dong said they hope to apply their river research to learn more about the geology that shapes other worlds.
“For future work, we will look to apply these measurements to other planets in our solar system and see what we can see,” Goudge said.
The research was funded by a postdoctoral fellowship to Dong from the National Science Foundation.
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