Answer: volcano

AnswerCrossword Clue
VOLCANO

It's dangerous when active

VOLCANO

Mars's Olympus Mons, for one

VOLCANO

Mount St. Helens, for one

VOLCANO
Occasional erupter
VOLCANO
Mauna Loa, e.g.
VOLCANOIt may be active
VOLCANOMount Rainier, e.g.
VOLCANOPeru's El Misti, e.g.
VOLCANOCone site
VOLCANOEl Misti, e.g.
VOLCANOWilshire, in a '97 film
VOLCANOGranite source
VOLCANOIsland group to which Iwo Jima belongs.
VOLCANOLassen or Stromboli.
VOLCANOLassen of Asosan.
VOLCANOWhat Popocatepetl is.
VOLCANOLassen, for example.
VOLCANOHekla, for example.
VOLCANOLassen or Hekla.
VOLCANOLassen, for one.
VOLCANOSpitfire, so to speak
VOLCANOStromboli, e.g.
VOLCANOSpot for a blowout
VOLCANOPyroclastic flow source
VOLCANOOne prone to blowing off steam