In the heart of Yellowstone National Park, a supervolcano releases around 45,000 metric tonnes of carbon dioxide each day.

But the magma chamber lying directly beneath its surface is not considered large enough to produce such levels, so researchers have been searching for an alternative source for years.

Now, by tracking seismic waves, a team of geophysicists has discovered an enormous secondary chamber deeper underground that's so large its partly-molten rock could fill the Grand Canyon 11 times over.

The Yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world. Silicic is used to describe magma or igneous rock rich in silica.

It is situated in Yellowstone National Park – which spans the midwestern US states of Wyoming, Idaho and Montana – and last erupted 640,000 years ago.