Is it true that the volcano in Yosemite can erupt,...?

Question

and the whole western United States will be covered by lava and, the rest of the world with a thick ash and blackness and end the world?

Answer 1

Probably not, but what it sits on is a caldera which is a volcano's crater. Scientists have a theory that it may erupt as a super-volcano that can wipe out everything in the western United States. The Earth may not be covered in ash but the Earth's average surface temperature will drop a couple degrees and may have the "Little Ice Age."

Answer 2

taint big enuff !

Answer 3

Portions of Yosemite sit atop a caldera. The caldera can erupt, but it's highly unlikely. Here is an article about calderas: http://en.wikipedia.org/wiki/Caldera