Incredible but true: scientists uncover a hidden process deep beneath California that could change geology forever

Deep under California’s Sierra Nevada scientists have discovered evidence of a hidden geological process that has long been suspected, but for which evidence has been hard to come by.

The Earth is made up of a number of layers. The outer solid layer we wander around on is called the crust, which sits on the upper mantle, which behaves like a viscous fluid - with some describing it as having the consistency of caramel.

Scientists have theorised that the bottom of the Earth’s crust may at times become denser than the mantle itself, leading to the sections breaking off and being subsumed into the mantle itself. This process has been named ‘foundering’.

Writing in the journal Geophysical Research Letters, scientists Vera Schulte-Pelkum and Deborah Kilb have spotted evidence of foundering occurring beneath California’s Sierra Nevada.

They spotted a curious number of small earthquakes, ranging in magnitude from 1.9 to 3.2, occurring at depths of 25 miles and more, where they would not usually be expected.

According to Schulte-Pelkum and Kilb, these earthquakes show a distinct layer in the mantle, which tapers off to the north, which they say backs up theories that a section of the Earth’s crust foundered below the southern part of the Sierra Nevada.

Why does foundering matter?

There are a number of reasons why proving that foundering happens and the processes it leads to are important.

By separating the denser lower part of the crust, foundering will influence the composition and evolution of the crust over time. While this process takes place over immense periods of time, it will help us understand what minerals we can expect to find in certain areas, helping geologists pinpoint areas that may hold important resources.

By removing the dense ‘root’ of the crust, foundering may lead to the uplift of the land, leading to the elevation of mountain ranges. Again, not something we will see happening before us in our lifetimes, but important to understand why some mountain ranges may be higher than we expected.

Foundering’s impact on volcanic activity and earthquakes

As dense material sinks from the bottom of the crust, hot mantle material may rise to replace it. This can lead to melting at the base of the crust and generate magma that can lead to volcanic activity. Foundering has been proposed to explain volcanic activity in certain areas.

Furthermore, foundering of the crust is believed to lead to deep-seated seismic activity. The earthquakes observed by Schulte-Pelkum and Kilb are believed to be related to foundering.

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