Something big is going on in California, down beneath the Sierra Nevada, and it’s happening very slowly. According to a recent seismic survey, delamination (deconstruction) seems to be happening. A dense portions of the lower lithosphere, including the mantle and lower Earth’s crust, are slowly sinking and peeling away.
The high elevation and steep eastern face of this famous mountain range in the United States can be explained by the lighter rock above bouncing and rising when that massive “root” falls off.
In order to see what is beneath our feet, geologists teams used vibrations that travel through the Earth. The photos show deformation mostly under the southern and central Sierra Nevada. Which are zones where dense lower crust and mantle lithosphere are separating from the plate that they used to be attached to, showing depths of about 60 to 100 kilometers.
Over millions of years, landscapes altering is the result of mountain roots shifting. The Sierra Nevada is one of the most obvious actual examples of how deep Earth processes can quietly change the surface. Similar ideas have been suggested for the Andes and the Tibetan Plateau before.
How geologists found what’s under the Sierra Nevada
To detect all of this things happening underground, geologists used seismic imaging, which consists on reading how earthquake-like waves move through different rocks.
And what did they found under the Sierra Nevada? Data showed anomalies that were consistent with delamination under the southern and central ranges. These signals suggest that dense lower crust and mantle lithosphere have begun to peel away between about 60 and 100 kilometers down. This would be something like removing a heavy backpack, and once the weight falls, the body (in this case, the upper Earth’s crust) can rise a little.
But is no like an earthquake, because it doesn’t happen suddenly. It’s actually a slow, deep adjustment that happen across geologic ages. The new photos fill in a gap in the California’s mountains stories connecting those surface signs to a process working far beneath.
What delamination means for landscapes
Delamination is an easy concept with huge consequences: when the dense root of a mountain range separates and collapses, the crust above can rebound and raise. This gives a clear explanation for Sierra Nevada’s constant high elevations. And also, we can learn more about how other continents change by zooming out from this experience. For the Tibetan Plateau and the Andes, similar processes have been suggested since the loss of dense lithospheric material there might also contribute to the retention of high peaks and huge relief.
The seismic photographs in the Sierra Nevada case provide extremely strong proof in today’s context, making it more than important.
This transparency work as reminder that the “map” of the United States is way more than just highways and rivers, and it help scientists to improve simulations of mountain construction: how ranges expand, stay high, or gradually drop.
Theres still questions to be answered
There’s already a lot of good information out; the seismic images point out to delamination of dense lithosphere in Sierra Nevada, and all of the involving the Earth’s crust and the mantle
But there is still some information left to know, the timing is still not define; when did this delamination started? Was it tens of millions of years ago? Did it happened in parts? Os is only recent? Those are open questions geologists are still left to test out with more data and better imaging.
The lesson for now is that landscapes change from the bottom up. And thanks to modern seismic tools, we can now connect what’s hidden deep below California all they way up to the skyline, so the rest of the answers might come up soon.