Pyroclastic flows are the worst a volcano can do other than simply blowing up. Debris at hundreds of degrees C go roaring down the side of the mountain at hundreds of miles an hour, carbonizing anyone in its path.
The Indonesian volcano Sinabung released a flow that killed 15 people and also spawned tornadoes.
"The pyroclastic flow deposits red-hot material on the slope of the volcano. After a few minutes, air heated by the deposit establishes a convective regime and due to the speed of the rising air a series of small tornados (also spelled tornadoes) are formed.
During daylight it is difficult to imagine how hot the deposit is. To see a pyroclastic flow deposit glowing at night from same location as present video one can view:"