To date, there has been no agreement among scientists on the link between avulsion and sea levels. Some believed it increased with rising oceans, others decreased for the same reason. There was simply no unifying theory to explain whether the frequency of river avulsion depended on sea level.
To clarify the phenomenon, researchers combined geomorphological and historical observations with a mathematical model on river dynamics. In doing so, they discovered that there are three ways in which deltas respond to rising oceans.
The first case occurs when a river has many sediments and the sea rise is relatively slow. Here the avulsion rates remain stable, making these rivers among the most resistant to rising oceans. In the second, the river has less sediment or the sea level rises more rapidly, and thus avulsion, aided by the deposits left by ocean waters, becomes more frequent.
In the last scenario, the most extreme, the rising of the sea exceeds the capacity of a river to deposit sediments. As the ocean infiltrates the delta, the river will reach its maximum avulsion rate and the entire system will begin to move inland.
What do rivers risk with global warming?
Rivers of the world, like Tiber, Danube, Nile, Rhine, Amazon River, Mississippi, Missouri or Yangzi, are the cradle of civilizations. Anyway the climate changes can make them in troubles.
A new study from the University of California, in collaboration with the California Institute of Technology, is investigating precisely effects of the climate changes on great rivers of the world. The study assessed the factors that determine the frequency with which avulsion occurs, i.e.
the rapid deviation of a stream from its original riverbed with the formation of a new river channel. This phenomenon leads to the detachment of land near the riverbed and is very common in river deltas in response to large floods, obstructions or earthquakes.
This process, in addition to having an impact on ecosystems, also has profound social implications: it can lead to civil unrest or economic collapse, destroying entire inhabited areas.