Possible Clues:

• Become active like 29-Down
• Eject lava, etc
• Go boom, volcano-style
• Spew ash
• Eject lava and ash
• See red revolutionary, innocent, given time
• Discharge what could be true about power
• Blow up in middle of Hertfordshire, in brief
• What volcano may do during another upthrust
• Defeat finally complete after reversal, lose it