is a “thermal feature” a steaming hole in the ground?
It most certainly is.
And Yellowstone, which happens to sit atop a MEGA volcano, is absolutely lousy with them.
...which all have combined to impress the H... out of sentient beings for centuries...
..or occasionally parboil/vaporize the Darwin Award types.
(I seem to recall that The Park bags one or two a year with the springs and the bears get a couple more fools...)