I remember watching it..................
Yellowstone interior areas with all the geysers, hot springs etc. is essentially a very old very large volcano’s caldera. That is a giant plug which sits atop deep channels down to a mass of lava. Not stable and has never been for the millions of years it has been there. The “level” of the ground is monitored and if it rises a certain amount, it is thought to be a sign a big one is coming. There are articles on the relative to sea level surface movements- pretty incredible stuff about which we can do nothing. The old lava flow from the original volcano can be seen over many states on relief geodetic maps. Lava rivers that were.