What Makes a Mountain 'Active' or 'Dormant'?

Imagine mountains as giant, sleepy giants. An active mountain is like a giant who still snorts and roars, it throws lava and ash out of its mouth (a volcano). A dormant mountain is one that's been quiet for a while but might wake up again someday.

If a mountain has had an eruption in the last 10,000 years, we call it active. If it hasn’t erupted in more than 10,000 years, it's dormant, but that doesn't mean it's dead. It might just be taking a long nap.