On 18-7-2013 20:01, MichaelJF wrote:
> I think as with all things in nature not all can be classified into the one or
> other category. I think the eruption with the following link is a mixture of a
> pyroclastic flow and a magma eruption (and the most magnificent eruption I ever
> found depicted):
> http://upload.wikimedia.org/wikipedia/commons/1/17/MountRedoubtEruption.jpg

True. The typical pyroclastic flow /sensu stricto/ runs along the 
topographic slope of the mountain. The lighter ash goes upwards. While 
the composition is identical, the pyroclastic flow is the coarser one 
and also to be found at the base of a typical tephra deposits, covered 
with an ash layer. They can show internal graded bedding but this is 
often obscured by the gas turbulence and the high density of the whole 
thing.

Thomas

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