GEOLOGY

Detailed explanation-1: -Dormant: Now things get a little dicier. The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest but could become active again. California’s Shasta is a dormant volcano by that definition (although could be considered “active” by some because it has erupted in historic times.)

Detailed explanation-2: -Volcanologists use that term as shorthand for “potentially active, ” so a “dormant” volcano is one that is not erupting now, but that is considered “active” because it could erupt in the future. Mount Hood is an active volcano that is currently dormant.

Detailed explanation-3: -Dormant volcanoes have not erupted for a very long time but may erupt at a future time. Extinct volcanoes are not expected to erupt in the future.

Detailed explanation-4: -Volcanoes go dormant because magma from the Earth’s mantle can no longer reach the volcano. For example, in Hawaii, the line of islands are slowly moving to the northwest. Meanwhile, the supply of magma stays in the same place within the Earth, which currently happens to lie beneath the Big Island.