How did the great pyramid of giza get 30 feet shorter?

The Great Pyramid of Giza was built around 2560 BC. It is believed to had then 481 feet while now it has about 455 feet. These approximately 30 feet that are missing are due to land movements, causing the pyramid to sink in the soil, as well as erosion. Over so many years since its construction, the pyramid has been exposed to strong winds and general weather erosion, much thanks to the type of stone that is its structure, as well, which is prone to erosion.