Rivers may seem as old as hills, but they have life cycles, just like other natural features. Many grow and leave their sinuous traces in the landscape, before eventually drying out. However, some rivers last longer than others. So, which river is the oldest in the world today?
The winner is older than the dinosaurs: Australia’s Finke River, or Larapinta in the indigenous Arrernte language, is between 300 and 400 million years old.
One of the strongest evidence of its ancient age is a geological anomaly called cross drainagesaid Victor Boulangergeomorphologist at the University of Arizona. Rather than flowing parallel to tough rock structures, such as quartzite, the Finke River passes through these tough mineral formations as it passes through the MacDonnell Ranges in central Australia.
Flowing water always takes the easiest path, making it counterintuitive that a river would flow against these hard rocks rather than along them. Therefore, the presence and origin of this cross drainage reveals crucial details about the historic course of the Finke.
“There are suggestions that there was pre-existing drainage that flowed as this range developed,” Baker told Live Science. “It’s called antecedence: basically, the river is there before the mountains formed, and as the crust rises, the river deepens.”
The MacDonnell Ranges (or Tjoritja in Arrernte) formed as part of the Alice Springs Orogeny – a mountain-building tectonic event that occurred 300 to 400 million years ago – making the Finke at least as old as these mountains.
Later evidence comes from erosion and weathering, which generate specific chemical profiles. This information indicates how and where the surface has interacted with the atmosphere and water flow over time. Using the radioactive signatures of certain isotopes (elements with different numbers of neutrons in their nuclei), scientists can also infer the ages of these rocks. Since radioactive isotopes decay at a fixed rate, it is possible to estimate when rocks formed by working backwards from the relative proportions of different isotopes. Together, these data points create a roadmap for piecing together the history and evolution of the Finke River.
But rivers are constantly changing: some grow larger from year to year and others dry up completely. So why did the Finke system last so long?
“Rivers can disappear if a massive influx of sediment overwhelms them (e.g., volcanic eruptions) or if the topography changes so drastically that flowing water takes a new course across the landscape (e.g., the advance and retreat of glaciers).” Ellen Wohlgeologist at Colorado State University, told Live Science in an email.
Additionally, “rivers may stop flowing due to climate change and/or human consumption of water,” Wohl said. “The long duration is favored by tectonic stability and the absence of glaciation during the period. Pleistocene” (2.6 million to 11,700 years ago).
In the case of the Finke, Australia has had an exceptionally stable landscape for a very long time. Situated in the middle of the Australian Plate, the continent has seen almost no significant tectonic activity over the past 100 million years, Baker said. Therefore, the Finke river system was able to develop and expand almost uninterrupted for most of its history.
As for the future, it is difficult to say how much longer the Finke will last.
“Rivers that have persisted for a long time will likely continue to persist,” Wohl said. However, “many dryland rivers” – such as the Finke – “are heavily altered by human water consumption”.
This phenomenon, she added, “is likely to increase in the future as global water consumption continues to rise and global warming makes many arid regions even drier.”
If the Finke ever dries up, the second could be the New River, which is now about 300 million years old, Baker said, and runs through Virginia, West Virginia and North Carolina.
