When Huey, Dewey, Louie pushes the round boulder over a cliff to block the geyser, the geyser erupts even bigger sending the rock up to Donald Duck and the Bear jumps on the rock and chases him even when night comes. Both Donald and the grizzly bear would've got tired very quickly due to being covered in fur and feathers and they would've likely fallen off the round boulder rock even before night came.
When Donald Duck is sitting in the geyser, he couldn't get out of the geyser in time, the geyser erupts and Donald is stuck swimming in the hot geyser. If Donald was touching the geyser he would get burned very badly since it's an active volcano, also he would actually fall off the erupted geyser on to the ground and not be stuck swimming in it.