Geologic features and durability of limestones at the sphinx

Geologic features considered to influence durability of the limestone at the sphinx are depositional history, evolution of porosity, and development of joints. These strata have two orthogonal groups of vertical joints. Where these joints intersect, wedge-shaped blocks are separating, causing loss of material from the core. Major reduction of the sphinx, however, is occurring due to salt crystallization aided by the ink-bottle pore systems prevailing in these rocks.The weathering profile exhibits alternating layers, less and more highly weathered. The less weathered rock is a biomicritic grainstone with smaller quantities of halite and gypsum and a larger large-pore-to-throat ratio than the indented, predominantly micritic, layers with larger concentration of salts and a smaller large-pore-to-throat ratio. Based upon poresize distributions, pressures generated in the pores have been calculated using thermodynamic principles, and an equation has been derived that provides a quantitative measure of durability of these rocks.