THE LAVA CAVES OF KHAYBAR, SAUDI ARABIA

Harrat Khaybar is a lava field ~12,000 km2 in area, located north of Medina in western Saudi Arabia. Its lavas and volcanoes are mildly alkaline and the age of its flows ranges from five million years old to historic. No speleological studies are known to have been carried out in Khaybar until Dahl Rumahah, a 208-m-long lava tube, located in northern Khaybar, was mapped in 2003. Rumahah was found to contain large quantities of bones of many kinds along with hyena, wolf and fox coprolites as well as a wooden gouging tool. Because calcite-rich water percolated through ceiling cracks, the cave is decorated with calcite stalactites, curtains and flowstone. In 2007, explorers found and mapped Umm Jirsan Lava Tube System, consisting of three passages separated by two collapses. This system has a typical ceiling height of 8 to12 m and some passages as wide as 45 m. With a total length of 1481.2 m, it is the largest surveyed cave system in Saudi Arabia and the longest lava-tube system in the entire Arabian Peninsula. It is expected that much longer systems will be discovered in Harrat Khaybar because Umm Jirsan is only one of some 40 strings of collapses mapped by helicopter in the 1980s. Caches of human and animal bones were found lying on the surface of meter-deep sediment in Umm Jirsan Cave, including a human skull fragment carbon dated at 4040±30 years BP and an unidentified animal bone 2285±30 years old. It is speculated that the surveyed caves may be three million years old, but Harrat Khaybar also has very young lava, suc