An Afar camel caravan crossing the salt flats of Lake Assal, Djibouti as shadows lengthen in the late afternoon.At 509 feet below sea level, Lake Assal is the lowest place in Africa. Because of extremely high midday temperatures, the Afar will arrive in the late afternoon and immediately set about collecting salt from deposits that are at least 109 feet thick. Each camel carries between four and ten thirty-pound sacks according to the size and maturity of the animal. The caravans leave again before daylight the following day. The salt is sold across the border in Ethiopia.