A mountain of human remains and animal carcases have been found in Saudi Arabia's Umm Jirsan, a vast underground tunnel that spreads for more than than 40 miles created by a river of lava ...Researchers found the gruesome mountain in Saudi Arabia's Umm Jirsan lava tube, which is thought to be the longest network of its kind in the country, measuring 4,900 feet long and around 26 to 29 feet. The "extremely dense accumulation of bones" was found on the lava tube's western passage...