Deposition is the process by which a substance changes from gas into a solid. Any substance can undergo the deposition process. During this process, the substance goes directly from a gas into solid, without going through the liquid stage in the process. The most common example of this process occurs when water vapor becomes ice. During the deposition process, the substance releases a substantial amount of energy into the environment. The energy release is in the form of heat.
Sublimation is the opposite of deposition. Sublimation is the process by which a substance moves directly from the solid state and into the gas state, bypassing the liquid state in between. Any substance is capable of undergoing this process, if the conditions are right. This occurs when ice sublimates into water vapor. Throughout the process, the substance takes in energy into the substance from the environment. The energy is in the form of heat.
The deposition process requires a low-pressure environment in conjunction with low temperatures. This normally occurs in clouds, as collections of gas gather. This also occurs during storms, as the water vapor in clouds undergoes a deposition into ice particles and falls to the earth's surface. Some ice particles melt during their return trip to the earth's surface, while others make it to the surface in the form of ice. The density of the gas contributes to the process, which you see when clouds reach a saturation point and begins the deposition process.
Sublimation requires a high-pressure environment and temperatures that are much higher than the substance's melting point. Lower temperatures cause the substance to melt, moving into the liquid state. This occurs most often in areas with very dry weather and severe temperature shifts. The sublimation process helps renew clouds and regulate temperatures in the environment.