 The magma that formed the Toledo and Vias caldera eruptions comes directly from the Earth's mantle. Scientists know this by studying the chemistry of the volcanic rocks around the caldera. The chemistry of those lava flows is very similar to the chemistry of the mantle. Another piece of evidence is the gases that are still coming out of the Vias caldera. These gases contain helium-3, which tells us that they come directly from the mantle. The helium collected from the gases released at Sodadam is the same as the helium collected from deep-sea smokers. When we look at seismic data of what is under the Vias caldera, we see a large magma body that is very different from the surrounding rock. This magma body is shaped like a cylinder that extends from 3 miles below the surface all the way down through the Earth's crust and into the mantle 13 miles deep. Another piece of evidence that there is very hot rock below the caldera is that there is an active geothermal system in and around the caldera. Experimental wells that were drilled 1800 feet deep have hit temperatures of 400 degrees Fahrenheit. The hot rocks deep below the caldera are not isolated. In fact, they have a profound impact on the Jemez River as it originates and flows out of the Vias caldera.