Pyroclastic

The eruption produced pyroclastic flows – a mixture of hot gas, lava and other volcanic material – that traveled up to two kilometers from the volcano’s crater.

Mount Merapi, Indonesia’s most active volcano, erupted Monday, sending plumes of ash into the air and pyroclastic flows down its slopes for a second straight day.

The word "ash" is not a very good one to include all the mechanical accompaniments of a subaerial or subaqueous eruption, since ash seems to be restricted to a fine powder, the residuum of combustion. A word is wanting to express all such accompaniments, no matter what their size or condition may be, when they are accumulated in such mass as to form beds of "rock." We might call them perhaps "pyroclastic materials," ...

Within sixty seconds, the entire area was razed by pyroclastic material with a temperature of nearly two thousand degrees Fahrenheit.

The basic volcanics are altered andesites, porphyritic diabases and andesites, and various pyroclastics.