When there is not enough water present to form one, a fumarole appears which can develop into a mud pot.
One of these natural phenomena is called Porkchop, and the oldest one in the world is thought to be Castle. A necessary condition for them to appear is a material of silicon dioxide which is dissolved from rocks, and which makes various channels pressure-tight and unable to leak into loose gravel or soil. When there is not enough water present to form one, a fumarole appears which can develop into a mud pot. Existing in "cone" and "fountain" varieties, they are created when hot volcanic rock superheats water that eventually forces the water above upwards. For 10 points, name this natural phenomenon that attracts many tourists to Yellowstone National Park to see Old Faithful.
One of these natural phenomena is called Porkchop, and the oldest one in the world is thought to be Castle.
{geyser}s