The emplacement, internal structure, distribution and longevity of such dams can be related variously to the amount, rapidity and duration of (primary) geothermal energy released, and the rock material made available; other considerations include the rock types produced, their physical and toughness characteristics, and their various modes of deposition. Depositional modes include gravity flow of molten lava at the surface, gravity flow or fall of pyroclastics through the air, as well as the redistribution and transportation of those materials by gravity and water.