Researchers tell us that salt is one of the causes of the damage. The ground in the area, including the Sphinx's limestone, contains salt naturally. Damage by salt is spreading fast in the following steps.
1) As wastewater from the growing city area increases, the level of water under the ground rises.
2) The salt in the limestone mixes with the water, and then crystallizes again on the surface of the Sphinx.
3) The crystallized salt makes cracks bigger.
In addition to the Sphinx, salt has damaged the Temple of Karnak in Egypt and Mohenjo-Daro in Pakistan. Some parts of the buildings are covered with salt. These historical structures show the great creativity of people in the past. It is ironic that they are facing a hard time now because of human-caused environmental changes.