Scientists found a massive lake or reservoir that is made up of molten carbon under the western U.S. Molten carbon is chiefly in the form of carbonate that could be harsh if it were to be released and considered to be a greater risk.

The findings of the study were published on Earth and Planetary Science Letters on April 1, 2017. It was led by geologists from Royal Holloway, University of London.

The study indicates that carbon rests 217 miles under the surface of the Earth in the upper mantle. It is about 700,000 square miles and could have the same area as Mexico. It has no direct pathway to the surface.

The scientists used the biggest array of seismic sensors in the world to identify what is there below the surface of the western U.S. There were 538 sensors that were utilized. This enables to produce a three-dimensional view of what lies beneath the subsurface.

They gauged the period it will take for sound to travel into the Earth and bounce back. It is known that various waves will bounce back at different times at various angles depending on the structure of the rock in the subsurface. They also discovered that the partially molten under the western U.S. could sequester at least 4.2 x 3 to the 17th power kg of volatiles. This could serve as a huge regional reservoir of volatile species like H or C.

So, how does this lake of molten carbonate exist? The molten carbonate exists because of the Pacific Plate subducting below the North American Plate. With this, it could trigger escalating high pressures and temperatures and with the combination of CO2 and water locked away the rock, there would be the partial melting of the plate, according to Forbes.

With this new study, the scientists theorized that the Earth's upper mantle may have about 100 trillion metric tons of carbon. On the other hand, the good news is that the release of the mantle's carbon occurs gradually over time chiefly through volcanic eruptions.