EROSION PROCESSES ON THE GREAT SPHINX AND ITS DATING
Many recent Egyptologists have attributed the carving of the Great Sphinx of Giza to the Old Kingdom Pharaoh Khafre (Chephren), ca. 2500 B.C. On the basis of a number of lines of geological, seismological, Egyptological, and related evidence, I have come to the conclusion that the structure commonly known as the Great Sphinx was built in stages (originally it may not have even been a Sphinx). Initial carving of the core body of the Sphinx is estimated to have taken place during the period of approximately 7,000 to 5,000 B.C. The Sphinx has subsequently been reworked and refurbished many times over the succeeding millennia -- including, probably, during the reign of Khafre. In particular, the rump or rear of the Sphinx was carved out much later than the core body, and the head of the Sphinx has been recarved.
My geological work suggests that Khafre merely restored the Sphinx.
The body of the Sphinx, carved from the local bedrock and thus sitting
in the bottom of an artificial hollow (ditch), and the walls of the Sphinx
enclosure exhibit well-developed precipitation-induced (p-i) weathering
(characterized by a rolling and undulating vertical profile) not typically
seen on Old Kingdom Giza Plateau structures (which exhibit primarily wind-induced
weathering marked by a more angular profile with soft layers removed by
wind abrasion) also excavated from the Mokattam limestone. This deep
p-i weathering of the Sphinx is interpreted as predating the current arid
regime of the area, and thus indicates that the body of the Sphinx predates
Old Kingdom times by perhaps several millennia. Though we continue
to refine our knowledge of the details of the paleoclimatic history of
the Giza Plateau over the last 10,000 years, we already know enough to
associate certain dominant modes of weathering with certain parts of that
climatic history. Portions of the Sphinx predate Old Kingdom times. The
temples adjacent to the Sphinx are built of limestone coreblocks taken
from the ditch quarried out to form the body of the Sphinx. These
coreblocks are faced with Aswan granite attributed to Khafre, but the coreblocks
were already deeply weathered when the granite facing was originally applied.
The first of several ancient repair campaigns to the weathered body of
the Sphinx was done with typical Old Kingdom style masonry, but the core
body of the Sphinx was already deeply weathered when this earliest repair
work was carried out (see Robert M. Schoch, 1992, KMT, A Modern Journal
of Ancient Egypt, vol. 3, no. 2, pp. 52-59, 66-70; Robert M. Schoch with
Robert Aquinas McNally, 1999, VOICES OF THE ROCKS, New York: Harmony Books).
Corroborative evidence includes low-energy seismic refraction data that
records up to 100\% deeper weathering below the original floor of the Sphinx
enclosure as compared to weathering seen in the identical limestones in
an area presumably quarried during Khafre's time in the rear of the Sphinx
enclosure. Seismic investigations have also uncovered a series of cavities
or chambers under the Sphinx (see Thomas Dobecki and Robert M. Schoch,
1992, Geoarchaeology, vol. 7, no. 6, pp. 527-544).