At atmospheric pressure, carbon would go from solid to gas. It needs to be compressed (which it apparently is, under the earth’s crust) to be liquid.
If it vented, we’d get some humongous flames.
"...Earth's interior is known for by its high temperatures where solid carbonates melt, creating distinctive seismic patterns."
The whole thing is a bit incoherent.
Reducing the pressure would allow part of the reservoir to evaporate, cooling the larger bulk remaining at the site of a leak.