An international team of researchers has discovered a curious geological phenomenon under the Andes mountain range: a trickle of parts of the earth’s crust into the mantle. This geological process would take place millions of years, causing wrinkles in the form of valleys on the surface of the Earth. The work has been published in the journal Communications Earth & Environment.
What is this drip?
The process is called “lithospheric dripping”, and it especially affects the earth’s crust. The heat from the Earth’s mantle causes some bordering areas of the crust to liquefy.
The molten rock falls little by little, accumulating in a point and causing the region of the crust in which it occurs to gain mass. That is, the drop that begins to form pulls the earth’s crust inward. The effect is the creation of a depression or valley in the earth’s surface.
The drop pulls inwards until a moment arrives when the drop finishes forming, separates from the outer layer and falls towards the interior of the planet, “like a drop of syrup or honey” explains Julia Andersen in the press release , who heads the authorship of the article in which the finding is reported. “We have confirmed that a deformation on the surface of an area of the Andean Mountains has a large portion of lithosphere underneath carried away as an avalanche”
How it affects the geography of the Andes.
When the drop is released, the tension with which it pulled the crust downwards also, with which it rises again, which causes peculiar striae to form in the initial basin. Although most of the process would be slow and negligible, this phase could have caused two tectonic events in the region in the past.
The discovery has been possible precisely thanks to the effect that this process has left on the orography of the land. The team simulated these conditions in the laboratory by creating scale models.
they showed markings on the surface similar to those that can be observed in the Arizaro region in the central Andes.
The team compared the results of the model they created “with geophysical and geological studies carried out in the central Andes, (…) and we found that changes in [la] Crustal uplift caused by dripping in our models followed very precisely the changes in elevation of the Arizaro Basin.”
“We also observed fold-like crustal shortening in the model, as well as basin-like depressions on the surface, so we are confident that a trickle is most likely the cause of the observed deformations in the Andes.”
Beyond plate tectonics.
The phenomenon of lithospheric dripping can help understand some geological processes beyond simple plate tectonics. This phenomenon may be of special relevance when studying extraplanetary geology, since planets like Mars and Venus do not have tectonic plates, but they are not necessary for phenomena like this trickle to occur.
Other examples of drip.
This is not the first time that indications of the presence of a lithospheric drip have been discovered. This could also occur in the central plateau of Anatolia, in Turkey and in the Great Basin, the region of the American West that covers most of the state of Nevada and part of other borders such as Oregon, California or Utah.
Although there are already several possible examples of this phenomenon, there are still many unknowns to investigate. According to the researchers, the response of the earth’s surface to this process is one of them.
This phenomenon has been compared to the famous tar drop experiment, also known as the longest experiment in history. In it a mass of pitch drips in a kind of hourglass. Due to its extreme viscosity, the drops take more than a decade to form. Perhaps it will serve to give us an idea of how it is possible for the ground we walk on to drip.
Images | Cover: Ben Stubbs, CC BY 2.0; interior: Julia Andersen et al., CC BY 4.0