• Caps can be moved in any direction, including diagonally.
• Erupting pieces are all moved in the same direction as the cap that triggered the flow.
• Caps (and erupting pieces) cannot be moved beyond the edge of the board.
• Caps (and erupting pieces) can be moved into any empty space, including the space in the center (called the Caldera) which only remains empty until a piece erupts into it.
• Moving a cap out of an empty square results in no eruption, and you can keep going.
• No piece can ever land on top of a cap.
• It’s OK to move a Cap back in the same direction it came from in order to cause an eruption.
Given these rules, many moves will cause no eruption because the erupting piece would either go off the board or land on a cap.