On the island Gullstruck, there are many volcanoes which often quarrel. This picture (Aarat, Turkey) shows what they could look like. When they are angry, the volcanoes in the story will shoot white hot ash that will kill anyone who gets near it
Erupting volcano - Most of the geodes that we find today were actually created when ancient Volcanoes erupted! As the lava cooled, air bubbles became trapped inside creating empty pockets. Over millions of years these pockets filled with the minerals which hardened into the beautiful crystal treasure we find today!