Possible Clues:

• Emulates Etna
• Explodes initially with violent spurt
• This puts the sudden outcome under 'er
• Comes out up in the rest
• Loses one's temper when the rest, running, catch up
• Breaks through, achieving backstreet clean-up
• It's the turn of the saint that's blameless that's blowing his top
• It comes out and comes up to keep the street clean
• Breaks out
• Makes like an angry volcano