Pre-modern causes of erosion theories.

Erosion of the Sphinx

The Sphinx was created by carving it from a single block of bedrock limestone measuring at 73 meters long by 20 meters high. The dates to witch archeologists determine the age of the monument to be is a mystery. Some suggest that the sphinx was crafted in the 4th dynasty while others think it was under repair during that time. It is even suggested that the sphinx was created before human kind walked the earth. The date that the sphinx was sculpted plays a very large role to determine the types of erosion to occur on the sphinx. This is due to the fact that different periods of time, different climates existed. This difference in humidity and temperature could lead to an increase in either mechanical or chemical weathering or any one particular type of weathering to take place.

Pre-modern causes of erosion theories

Sand: Almost all of the theories as to how the sphinx was eroded have reference to sand being a contributing factor. This is mainly due to that most archeologists agree that most of the sphinxes life, it has been covered in sand. Also sand has been around the sphinx for almost all of its life increasing the chance of sand being picked up and thrown into the sphinx by the wind.

Ground water erosion: From looking at the paws of the Sphinx archeologists believe that ground water caused some erosion to the sphinx. A theory was proposed that groundwater rose up through capillary action which in turn reacted with the limestone. 500 years after this event the water dropped down and never occurred again, to this date. However many arguments have been put forward against this theory such as:

To rise from a much deeper level than it is at present level seems unlikely.
To erode two feet deep channels into the body of the Sphinx, and ...

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To rise from a much deeper level than it is at present level seems unlikely.
To erode two feet deep channels into the body of the Sphinx, and the walls of the quarry pit, in the span of five hundred years seems unlikely.
For this water to all of a sudden rise to this high level and never again seems unlikely.
The other buildings around the area were not effected by this capillary action
The Temple of Khafra is 46 meters above the Giza plateau but has similar appearances of erosion.

Water erosion: The theory that the sphinx had been eroded by water was suggested due to the features of the outer layer of the sphinx. The buildings around the sphinx e.g. the temples showed that the outer rock was worn badly and “sagging.” Deep fissures could also be found in the heavily rounded rock. The cause for this erosion by water is suggested to be due to the flooding of that period between 10,000 to 5000BCE. Due to the Sphinx positioned bellow the Giza plateau it is believed that water overtime though surface run off collected around the sphinx causing flooding. This can strongly bee seen in the capillary action.

Salt crystallization: The middle of layer has been examined and shown to be slightly more pours when compared to the limestone at the top and bottom of the sphinx. Due to this larger size it has made the limestone more prone to salt crystallization. This is the process where morning moisture evaporates during the day leaving water molecules in the pores. These expand when set, causing the rock to break up.

Wind erosion: It is argued weather or not the wind combines with sand to actually protected or eroded the sphinx. Some archeologists believe that sand was picked up by fast winds and hurled against the sides of the sphinx, and due to this small force causing the rock to break down over a long period of time. Other archeologists believe that due to the Sphinx being located in a hollow and that it has mainly been covered in sand for the most part of its life; this actually protected other forms of erosion as this built up as a protective layer.

Modern causes of erosion.

Pollution: Pollution never really existed until the 20th centenary and since the start of the 20th century has rapidly increased. Limestone reacts with acid rain causing it to erode very rapidly (in geology terms). Acid rain is caused by pollution, more specifically carbon monoxide mixing with the clouds in the air. Carbon monoxide is emitted in the burning of fossil fuels such as oil and coal. Automobiles are the greatest contributor to the emission of carbon monoxide into the atmosphere causing acid ran to fall. The most common way to reduce carbon monoxide emission into the air from automobiles is by attaching a catalytic converted into the exhaust funnel in a car.