Subsurface Ice and Permafrost on Mars

Abstract

Terrestrial permafrost varies widely in its physical and mechanical properties and behavior. Ice content, for example, may range from 0 to 100 % by volume. The types of subsurface ice are numerous and the crystal structure of terrestrial subsurface ice is variable. Most subsurface ice is hexagonal, Ice-I; clathrate structures are known, however. The ice content of permafrost is only a fraction, albeit the predominant one, of the water present. A significant portion of the water present exists in an unfrozen state and is distributed throughout the pore space and in interfacial areas. The proportion of ice to unfrozen water varies, in a characteristic manner, with temperature and solute concentration. These basic facts are important In determining the strength and deformation properties of permafrost and also its hydrological and electrical properties. Reliable relationships among these properties are derivable from basic thermodynamic theory and from empirical relationships recently established on the basis of laboratory and field data.