THE SPHINX

[8] See, for instance, the work by Gauri and his colleagues cited above, as well as the following: A. N. Chowdhury, A. R. Punuru and K. L. Gauri, 'Weathering of limestone beds at the Great Sphinx," Environ. Geol. Water Sci. 15 (1990), 217-223; K. L. Gauri and A. R. Punuru, 'Characterization and durability of limestones determined through mercury intrusion porosimetry,' in F. Zerra, ed., The Conservation of Monuments in the Mediterranean Basin (Proc. First Intern. Syrnpos. Bari, 1989), 255- 258; A. R. Punuru, A. N. Chowdhury, N. J. Kulshreshtha and K. L. Gauri, 'Control of porosity on durability of limestone at the Great Sphinx, Egypt,' Environ. Geol. Water Sci. 15 (1990), 225-232. See also, C. Hedges, 'Sphinx poses riddle about its fate: Experts ponder ways to save monument from man and time,' New York Times (10 March Redating the Sphinx), C4.

[9] In their work on the weathering of the Sphinx, Gauri and his colleagues (see references cited above) have suggested that, in general, the upper beds of the middle member (Member II or Setepet Member) of the core body or thoracic region of the Sphinx are more durable than the lower beds. These authors have calculated durability factors for different beds of this member; such factors range from about 100 (high durability) for the uppermost bed, just below the neck of the Sphinx, to about 11 for the lowermost bed of the member. There is a general trend of increasing durability factors, as calculated by these authors, going up section. Thus, their bed 4i (located approximately halfway up the body of the Sphinx) has a calculated durability factor of 75 (see summary of this work in Gauri et al., 1988).


          The primary factor that determines the durability of the various beds, according to Gauri and colleagues, is the relative pore-size distributions in the various beds (they calculated their durability factors on the basis of the relative volume of the pores in various beds). In summary, stone with a greater volume of large pores will tend to be more durable. The reason for this is explained succinctly by Gauri et al. (1988, 727-728): "The influence upon durability of the interconnected small and large pores may also be visualized qualitatively in terms of transport of water through stone. Large pores become easily filled due to the mass movement of water into the pores. But when pores communicate with the exterior of the stone through narrow throats, the throats influence the filling of the large pores. Small (narrow) capillaries have large suction. An abundance of these capillaries will fill the small and large pores completely. But if many large pores are present and the small capillaries are somewhat larger, some empty space may then continue to exist in the stone. When crystals begin to grow in a solution, the resultant pressure will be experienced on the walls of the completely filled pores, but such pressure will be 'released' in the empty space of the partially filled pores. Consequently, stone with a large volume of large pores and a small volume of narrow capillaries will be more durable."