I've spent the morning viewing clips of lahar on a site below someone posted above, I think; if not, someone posted the link somewhere in a thread related to lahar.
To the point, I searched out some pyroclastic terms that may be of interest to those interested in volcanoes. Many that I found I'll omit in deference to those who won't want an unusually long post:
pyroclast-- Volcanology. an individual particle or fragment of clastic rock material of any size that is formed by volcanic explosion or ejected from a volcanic vent.
http://www.harcourt.com/dictionary/def/8/3/1/4/8314100.html
pyroclastic ground surge Volcanology. the comparatively thin layer of rock of varying thickness found around a volcanic vent.
http://www.harcourt.com/dictionary/def/8/3/1/4/8314400.html
pyrogenesis Geology. 1. the intrusion and extrusion of a magma. 2. the products derived from a magma.the products derived from a magma.
http://www.harcourt.com/dictionary/def/8/3/1/5/8315400.html
pyroschist Petrology. a schist or shale with sufficient carbon to burn with a bright flame or to yield volatile hydrocarbons upon heating.
http://www.harcourt.com/dictionary/def/8/3/1/8/8318600.html
...now if I could just relocate the site that had the eerie photographs of pillow lava...
Oh, and here's the site that has the footage of lahar in action:
http://www.geo.mtu.edu/volcanoes/pinatubo/lahar/
WW