Would there be any warning?
Probably not. The last significant explosion in the park was at a place called Pork Chop Geyser in 1989. That left a crater about five meters across—not huge by any means, but big enough if you happened to be standing there at the time. Fortunately, nobody was around so nobody was hurt, but that happened without warning. In the very ancient past there have been explosions that have made holes a mile across. And nobody can tell you where or when that might happen again. You just have to hope that you're not standing there when it does.
Big rockfalls are also a danger. There was a big one at Gardiner Canyon in 1999, but again fortunately no one was hurt. Late in the afternoon, Doss and I stopped at a place where there was a rock overhang poised above a busy park road. Cracks were clearly visible. "It could go at any time," Doss said thoughtfully.
You're kidding, I said. There wasn't a moment when there weren't two cars passing beneath it, all filled with, in the most literal sense, happy campers.
Oh, it's not likely, he added. "I'm just saying it could. Equally it could stay like that for decades. There's just no telling. People have to accept that there is risk in coming here. That's all there is to it."
As we walked back to his vehicle to head back to Mammoth Hot Springs, Doss added: "But the thing is, most of the time bad things don't happen. Rocks don't fall. Earthquakes don't occur. New vents don't suddenly open up. For all the instability, it's mostly remarkably and amazingly tranquil."