An answer to the sphinx's problem.

An answer to the sphinx's problem

Researchers from the University of Louisville are attempting to save an endangered creature that has sat for almost 5,000 years as a guard to the great Egyptian pyramids. Carved out of a limestone knoll, the sphinx has spent most of the millennia buried up to its neck in the desert sands. But workers cleared away the protective sand in the late 1800s, and weathering has started to claim the lower portion, causing Egyptian officials to fear that the monument might suffer irreparable damage.

For most of the last decade, K. Lal Gauri, director of the Stone Conservation Research Laboratory at the University of Louisville, has studied the decay of limestone at the sphinx. Early on, he discovered that the weakest rock layers contained high salt concentrations. Recently, however, he has discovered how salts have contributed to the decay.

During the cool desert nights, moisture condenses inside the pores of the limestone and dissolves the embedded salts. Then when the sun heats the stone in the day, the salts recrystallize, creating pressure in the pores of the stone that can break the limestone apart. Rocks with the smallest pores are the most susceptible to weathering because the tiny pores draw moisture further into the interior of the stone. These findings, says Gauri, are aiding those who are selecting replacement stones for restoration work on the sphinx.