Geology behind the Sphinx

In geological Eocene times, some 50 million years ago, most of present-day Egypt was submerged under the sea. Sedimentation and decomposing remains of marine organisms formed a carbonated mud. As the sea receded, mud petrified into a consolidated and hardened sedimentary rock, forming banks of limestone from which the pyramid builders quarried limestone blocks and from which they carved the Sphinx.
Natural limestone of the Giza Plateau in which lowest layers the Sphinx is carved is known as the Mokkatam Formation. Sphinx geological layers have been labeled as Member I, Member II, and Member III.

The Figure displays a simplified cross-section of the Giza Pyramids Plateau. The Giza Plateau is an outcrop of the Middle Eocene Mokkatam Formation. A second outcrop of the Upper Eocene Maadi Formation borders the Pyramids Plateau. A large sandy wadi separates the Mokkatam Formation from the Maadi Formation.

The Sphinx within the Giza geology

The lowest stratum of the statue, Member I, is the hard and brittle rock of an ancient reef limestone containing nummulite fossils easy to identify. This layer rises to a height of four meters at the Sphinx’s rump and only one meter at the paws.

Most of the Sphinx body is cut into Member II, seven layers that alternate softer and harder limestone, marls and claystone, as they rise in elevation. This layers show large flakes of marly limestone blow off the walls of the Sphinx quarry and since ancient times until recent restorations, most of the Sphinx body was protected by masonry cover.

Member III, from which the neck and head are carved, is softer at the neck and harder at the head. This is a good building stone. Member III’s durability explains the remarkable preservation of the Sphinx’s face while the statue’s body has been ravaged by weathering.

What happended to the nose…?

Legends have passed over hundreds of years regarding this question: What happened with the Sphinx’s nose?

Many of us have heard the tale that a cannonball fired by Napoleon’s soldiers hit the nose and caused it to break off. This is not true, since sketches of the Sphinx published well before the era of Napoleon  illustrate it without a nose…

The Egyptian Arab historian al-Magrizi wrote in the 15th century that the nose was actually destroyed by a Sufi Muslim named Muhammad Sa'im al-Dahr. In 1378 Egyptian peasants made offerings to the Great Sphinx in the hope of controlling the flood cycle, which would result in a successful harvest. Outraged by this blatant show of devotion, Sa'im al-Dahr destroyed the nose and was later executed for vandalism. Whether this is absolute fact is still debatable.

Long-term deterioration

With the Sphinx rapid erosion, age has been set to be not older than 4,500 years, tied to Pharaoh Khafre’s building program at Giza.

Until recent years, the Sphinx was still disintegrating. In the 1980s, two sizeable stones fell from the statue: masonry veneer from the left hind paw in 1981 and a large piece of bedrock from the right shoulder in 1988. The Supreme Council of Antiquities’ decade-long restoration in the 1990s was only the latest of the repairs to the Sphinx that began at least in the New Kingdom (1550-1070 BC).