The terms earth, water, fire, and air, refer to the four elements — solidity, fluidity, temperature, and motion.
The air element is not just wind, but any kind of elemental pressure or motion. (Gastric wind, whether it comes up or goes down, is also the air element). The water element is not just water, but also molten rock or molten iron — even ice contains the fluid element, which is why glaciers flow.
Earthquakes occur due to the movement of magma (which is water element), forced up by pressure (air element). Cohesion is a quality of water too, when cohesion is weak faults start to slide.
• • • • (Upasampadā: 24th June, 1979)