against volcanic vents. Pendant shaped tower tombs or cairns in Harrat Khaybar have been dated back to the third millennium BCE. Similar funerary structures dating to the Middle Holocene are found within a range spanning across northwestern Arabia, although a particularly high density have been found in Harrat Khaybar. These groupings of structures are associated with the oases along the fringes of Harrat Khaybar. Keyhole and trumpet tombs, tomb structures not found elsewhere, have also been discovered in Harrat Khaybar. Researchers have studied hundreds of large stone structures nicknamed "desert kites" and "gates", but their exact purpose and function is still unknown. The gates of Harrat Khaybar are so named because they resemble horizontally laid barred gates. This type of structure is rarely attested to outside of Harrat Khaybar. The largest of the gates measure over 304 metres (1,000 ft) in length and 75 metres (250 ft) in width. It has been theorized that desert kites may have been used to trap and hunt wild animals. In particular, it has been theorized that they were used to corral herds of gazelles. The kites found in Harrat Khaybar are similar to other stone structures found in neighboring Syria and Jordan. However, many of the kites of Harrat Khaybar are built in a different shape than those found elsewhere. In 2004, neurologist Abdullah al-Saeed first began studying the structures in the lava fields and found them to be unimpressive, but reassessed their importance after reexamination of the area by the use of Google Earth. According to al-Saeed, he and his team did not observe the pattern and importance of the structures until observing them from an aerial viewpoint. Al-Saeed and his team later collaborated with British archaeologist David L. Kennedy, who had used aerial archaeology to study similar structures in Jordan, but had not been allowed to cross the border into Saudi Arabia. According to Kennedy, the structures in the Harrat Khaybar were created between 2,000 and 9,000 years earlier than those in Jordan. As of 2017, the team of researchers had reportedly discovered more than 900 kites in Harrat Khaybar. Umm Jirsan lava tube Within the lava field is the Umm Jirsan lava tube, with a length of in three sections including two pieces of collapsed roof. It is Saudi Arabia's longest lava tube system. In August 2021, the analysis of many thousands of animal and human bones from the cave