Chemistry The act or process of turning a gas into a liquid. Liquefaction is usually achieved by compression of vapors (provided the temperature of the gas is below the critical temperature), by refrigeration, or by adiabatic expansion.
Geology The process by which sediment that is very wet starts to behave like a liquid. Liquefaction occurs because of the increased pore pressure and reduced effective stress between solid particles generated by the presence of liquid. It is often caused by severe shaking, especially that associated with earthquakes.