Stanford scientists reveal that meandering rivers existed lengthy earlier than vegetation stabilized their banks, difficult a central narrative in geology.
A workforce of Stanford researchers is difficult a long-standing concept that the emergence of land vegetation about 500 million years in the past dramatically altered the best way rivers regarded and behaved.
Rivers usually fall into two principal classes: braided rivers, the place a number of shallow channels weave round sandy bars, and meandering rivers, the place a single channel carves sweeping curves throughout the panorama. For many years, geologists believed that earlier than vegetation developed, rivers had been largely braided, and that meandering patterns solely appeared as soon as vegetation anchored riverbanks and trapped sediment.
The brand new findings, revealed within the journal Science, argue that this view misreads the geological document. The examine exhibits that even rivers with out vegetation can meander, abandoning deposits that carefully resemble these created by braided rivers. This distinction issues as a result of the type of a river influences how lengthy sediment, carbon, and vitamins stay saved in floodplains, shaping each ecosystems and local weather over Earth’s historical past.
“With our examine, we’re pushing again on the extensively accepted story of what landscapes regarded like when flora first developed on land,” mentioned lead creator Michael Hasson, a PhD scholar in Mathieu Lapôtre’s lab on the Stanford Doerr College of Sustainability. “We’re rewriting the story of the intertwined relationship between vegetation and rivers, which is a major revision to our understanding of the historical past of the Earth.”
The muddy floodplains of meandering rivers – dynamic ecosystems created over hundreds of years by river overflow – are among the many planet’s most considerable non-marine carbon reservoirs. Carbon ranges within the environment, within the type of carbon dioxide, act as Earth’s thermostat, regulating temperature over huge timescales. Precisely budgeting for the carbon caches created by meandering rivers might assist scientists construct extra complete fashions of Earth’s historic and future local weather.
“Floodplains play an necessary function in figuring out how, when, and whether or not carbon is buried or launched again into the environment,” Hasson mentioned. “Based mostly on this work, we argue carbon storage in floodplains would have been frequent for for much longer than the basic paradigm that assumes meandering rivers solely occurred over the past a number of hundred million years.”
The place the river flows
To gauge vegetation’s influence on river channel patterns, the researchers examined satellite tv for pc imagery of about 4,500 bends in 49 current-day meandering rivers. About half of the rivers had been unvegetated and half had been densely or partly vegetated.
The researchers keyed in on level bars – the sandy landforms that develop on the within bends of meandering rivers as water movement deposits sediments. In contrast to the sandy bars that type in the midst of braided rivers, level bars are inclined to migrate laterally away from the facilities of rivers. Over time, this migration contributes to meandering rivers’ characteristically sinuous channel shapes.
Recognizing that these sandy bars type elsewhere based mostly on river type, geologists for many years have measured the trajectory of bars within the rock document to disclose historic river paths. The rocks, usually of sandstones and mudstones, present proof for divergent river types as a result of every deposits totally different sorts of and quantities of rock-forming sediment, giving geologists clues for reconstructing long-ago river geometries. If sandstones confirmed little variation within the angle of bar migration, geologists interpreted the bars as transferring downstream, and thus {that a} braided river created the deposits.
Utilizing this system, geologists had seen that rivers modified the best way they behaved across the time that vegetation first developed on Earth. This statement led to the conclusion that land vegetation made river meandering potential, as an example by trapping sediment and stabilizing riverbanks.
“In our paper, we present that this conclusion – which is taught in all geology curricula to at the present time – is almost certainly incorrect,” mentioned Lapôtre, the paper’s senior creator and an assistant professor of earth and planetary sciences on the Doerr College of Sustainability.
By taking a look at trendy rivers with a variety of vegetation cowl, the researchers confirmed that vegetation persistently change the path of level bar migration. Particularly, within the absence of vegetation, level bars are inclined to migrate downstream – like mid-channel bars do in braided rivers.
“In different phrases, we present that, if one had been to make use of the identical criterion geologists use in historic rocks on trendy rivers, meandering rivers could be miscategorized as braided rivers,” Lapôtre mentioned.
Rivers over time
The findings provide a provocative new window into Earth’s previous eons, upending the standard image of how rivers have sculpted continents. If certainly carbon-loaded floodplains had been laid down much more extensively over historical past, scientists might must revise fashions of main pure local weather swings over time, with implications for our understanding of ongoing local weather change.
“Understanding how our planet goes to answer human-induced local weather change hinges on having an correct baseline for the way it has responded to previous perturbations,” Hasson mentioned. “The rock document supplies that baseline, however it’s solely helpful if we interpret it precisely.”
“We’re suggesting that an necessary management on carbon biking – the place carbon is saved, and for the way lengthy, attributable to river sort and floodplain creation – hasn’t been absolutely understood,” he mentioned. “Our examine now factors the best way to higher assessments.”
Reference: “Vegetation adjustments the trajectory of river bends” by Michael Hasson, Alvise Finotello, Alessandro Ielpi and Mathieu G. A. Lapôtre, 21 August 2025, Science.
DOI: 10.1126/science.adv4939
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