Possible Clues:

• Opening in a planet's crust allowing lava to escape
• Volume company supports, including article that’s hot stuff in it?
• Mount Etna, for instance
• Krakatoa or Vesuvius, eg
• Where you'd be lucky to find four leaves (-- er, no!) climbing conical hill
• Oval cone not completely reshaped?
• One potentially explosive book half concealed by accountant, isn't it?
• Book accountant required just after climbing mountain
• Granite source
• Performing on vocal my output is hot stuff