what is a pyro claustic flow?

If I understand what you're asking correctly, it isn't a pyroclastic flow until it's actually ejected from the volcano. The volcano eruption is caused by the magma chamber below either exploding or erupting, and each volcano eruption is a little bit different. I'm not sure exactly which conditions lead to pyroclastic flow; you'd have to do some research on that.

You mean "pyroclastic" which is a cloud of superheated gases and debris which flows down the side of a volcano at speeds up to hundreds of miles per hour.

You cannot outrun these and you die from having your lungs boiled inside your body and your flesh cooked instantly as you run. Sort of like a nuclear explosions effects on your body without the radiation!!

probably should be in "Earth Sciences and Geology" instead of geography

Is is when A volcano blows up and there is a huge avalance of super heated rock and vapors that fly thorugh the landscape and destroy everything in its path its like a snow avalance but thousands of degrees hotter.

a cloud of super hot dust and ash that is ejected from a volcano. It travels at like 900 miles per hour.

Pyroclastic - "Broken by fire" The shattered debris of a violent volcanic eruption. If the lava flows around the debris and glues it all together again, you get what's called pyroclastic breccia.

The liquid rock that spews out of the earth's mantle via a volcano...

The results of a volcano. Pyro means fire.

pyroclastic flow, a dense cloud of gases and ash," pyro"-fire, "klastis"- broken ( pyroclastic materials).(greek " ")