21.   Scientists say more molten rock will produce more explosions, ash clouds and avalanches of fiery rock and gases called pyroclastic flows.

22.   Such eruptions are particularly dangerous because the mixture -- called a pyroclastic flow -- moves much faster than lava, and can easily outpace emergency vehicles.

23.   That volcano awakened scientists to the existence of pyroclastic flows and started a line of research that is still continuing.

24.   The statement said that pyroclastic flows, which are fast-moving clouds of ash, rocks and gases heated to hundreds of degrees, are occurring regularly.

25.   There had been three smaller internal explosions Wednesday, but they were not powerful enough to cause any pyroclastic flows.

26.   There were three small internal explosions Wednesday, none powerful enough to cause any pyroclastic flows.

27.   Volcano expert William Ambeh, who is in charge of the observatory, warned that more pyroclastic flows were expected and with greater frequency.