RUB’ al KHALI (Arabic : EMPTY QUARTER) is the largest continuous sand desert in the world, encompassing most of the southern third of the Arabian Peninsula. The desert covers some 650,000sq.km, including parts of Saudi Arabia, Oman, the UAE and Yemen. It is part of the larger Arabian Desert.
The Desert is 1,000km long and 500km wide. Its surface elevation varies from 2,600ft in the southwest to around sea-level in the northeast. The terrain is covered with sand dunes with heights of up to 820ft, interspersed with gravel and gypsum plains. The sand is a reddish-orange colour due to the presence of FELDSPAR. There are also brackish salt flats in some areas, such as the UMM al SAMIM area on the desert’s eastern edge.
Along the middle length of the desert, there are a number of raised, hardened areas of calcium carbonate, gypsum, clay that were once the site of shallow lakes. These lakes existed during periods from 6,000 to 5,000 years ago and 3,000 to 2,000 years ago. The lakes are thought to have formed as a result of “cataclysmic rainfall” to present-day monsoon rainfall and most probably lasted for only a few years. However, lakes I the MUNDAFEN area in the southwest of the RUB’ al KHALI show evidence of lasting longer, up to 800 years, due to increased runoff from the TUWAIQ ESCARPMENT.
Evidence suggests that the lakes were home to a variety of flora and fauna. Fossil remains indicate the presence of hippos, water buffalo and long-horned cattle. The lakes also contained small snails, OSTRACODS, and when conditions were suitable, freshwater clams. Deposits of calcium carbonates and opal PHYTOLITHS- indicate the presence of plants and algae. There is also evidence of human activity dating from 3,000 to 2,000 years ago, but no actual human remains have been found.
Fauna includes arachnids (e.g. scorpion) and rodents, while plants thrive throughout RUB’ al KHALI. As an eco-region, it falls within the Arabian Desert and East Sahara-Arabian xeric shrub lands.
Geologically, RUB’ al KHALI is the most oil-rich site in the world. Vast oil reserves have been discovered underneath the sand dunes. SHEYBA, at the north-eastern edge of RUB’ al KHALI, is a major light crude oil-producing site in Saudi Arabia. GHAWAR, the largest oil field in the world, extends southwards into the northernmost parts of RUB’ al KHALI.
Desertification has increased through the millennia. Before desertification made the caravan trails leading across the RUB’ al KHALI so difficult, the caravans of the frankincense trade crossed the now virtually impassable stretches of wasteland until about AD300. It has been suggested that UBAR or IRAM, a lost city, depended on such trade. The traces of camel tracks, unidentifiable on the ground, appear in satellite images.. More recently, tribal populations were also present in certain parts of RUB’ al KHALI. A few road links were connected with these tribal settlements to the water resource and oil-production centres.