Valley of the Kings rains. There is currently little year-round rain in this part of Egypt, but there are occasional flash floods that hit the valley, dumping tons of debris into the open tombs. The quality of the rock in the Valley is inconsistent, ranging from finely-grained to coarse stone, the latter with the potential to be structurally unsound. The occasional layer of shale also caused construction and conservation difficulties, as this rock expands in the presence of water, forcing apart the stone surrounding it. It is thought that some tombs were altered in shape and size depending on the types of rock the
Valley of the Kings lecture inside the tombs, and visitors are expected to proceed quietly and in single file through the tombs. This is to minimize time in the tombs and prevent the crowds from damaging the surfaces of the decoration. In 1997, 58 tourists and four Egyptians were massacred at nearby Deir el-Bahri by Islamist militants from Al-Gama'a al-Islamiyya. This led to an overall drop in tourism in the area. On most days of the week an average of 4,000 to 5,000 tourists visit the main valley. The West Valley is much less visited, as there is only one tomb that is open