YELLOWSTONE National Park is ever changing, as a gigantic ancient, super volcano, that's not dead yet.
Even the park's paved roads are not immune to geothermal effects: Recent example from an official Yellowstone National Park Service (NPS) news release (and yet apparently NOT reported by news organizations): the Firehole Falls Road.
Back in July of 2014, extreme heat from surrounding thermal areas caused thick oil to bubble to the surface, damaging the blacktop roadway and creating unsafe driving conditions on the popular, scenic, one-way road, located off the Grand Loop Road, just south of Madison Junction in the park’s Lower Geyser Basin.
So, although the one-way (southbound) road did eventually reopen, the Park Service apparently took most of the parking away at the swimming hole area with log fence barriers, just to be safe. Proves, once again, even nature's treasures are fragile.
When I traveled this road in October of 2012, there was parking for a dozen or so cars right by the swimming hole at Fire Hole. Now, October of 2014, there is essentially none, without blocking the road.
The only parking is 400 yards or so to the south or the north of the Fire Hole "pool," so you have to walk.
(Of course, you could block the road, as I almost ran into a woman who unsafely and un-smartley left her car on the narrow, winding Fire Hole road -- and her door open -- to go meander around, as if she was the only one driving the road!!!)
There is only one other official swimming area in Yellowstone: Boiling River. You used to be able to swim there throughout the summer, but never in recent years.
Now Boiling River isn't open for swimming until mid to late summer, when water is lower on the Gardiner River. Even then, it is a half-mile walk from a parking area to the "hole."
Hot and cold water mix here and it is warm, spa-like water there (as I have been there.)
By the way, the NPS claims the Fire Hole Falls swimming area has no direct thermal input to the river there -- that it is just swimming pool temperature water, heated gradually from elsewhere along the river.
-I'm also amazed how little of Yellowstone's weather or thermal effect incidents go unreported by the media.
EXAMPLE: Mid-June of 2010. An overnight ice storm closes the loop road from Tower Falls to Canyon. The road is closed from morning one day, until late afternoon and required an hour-plus detour.
Also, the NPS doesn't tell (or can't readily communicate with) the ranger at the Mammoth/north entrance to the park about the closure. You only found out about this closure by driving to Tower Falls, as I did, and seeing the barriers on the roadway.
This also illustrates, communication wise, how poorly Yellowstone Park could handle a true disaster. The park is huge, rustic and apparently lacks a good communication system.