Among these are the hydrosphere, including the oceans, lakes, rivers and groundwater, and the cryosphere formed by the snow and ice masses of the earth. Hydrosphere geophysics can therefore be divided to three disciplines: Physical oceanography is the study of hydrography and hydrodynamics describing the properties and motion of seawater; Hydrology examines the freshwater systems of the earth; and Cryology is the study of snow cover, glaciers, lake and river ice, sea ice and frozen ground.