The Furnace Floor
The Turpan Depression is a 50,000-square-kilometer fault-bounded trough, a piece of Earth's crust that has sunk relative to its surroundings. Its lowest point, the salt flats of Aiding Lake, sits at 154 meters (505 feet) below sea level, making it the second or third lowest land depression on the planet. This extreme depth is a primary factor in its intense heat. The basin is ringed by high mountains, including the Bogda Shan range, which block moist air and create a severe rain shadow. Annual precipitation averages a mere 15.7 millimeters, while the potential evaporation rate is a staggering 3,000 millimeters.
The geology of the region amplifies the effect. The famous Flaming Mountains, a range of barren, red sandstone hills running through the depression, are part of this natural furnace. Formed during the tectonic plate collisions that created the Himalayas, these mountains are composed of red sandstone from the Jurassic, Cretaceous, and Tertiary periods. This dark-colored rock has a low albedo, meaning it absorbs a high percentage of incoming solar radiation. In summer, with clear skies and intense sunlight, the ground surface temperature of these mountains can exceed 70°C (158°F), with some measurements reaching as high as 82.3°C. This absorbed heat radiates into the air, which becomes trapped within the enclosed basin, forming a persistent heat island.
Life in the Oven
Despite the harsh conditions, the Turpan Depression is an important oasis and agricultural center for millennia. Human ingenuity overcame the extreme aridity through the creation of the Karez irrigation system. This ancient technology, with a history dating back over 2,000 years, consists of a network of underground tunnels that tap into groundwater from the base of the Tian Shan mountains and channel it for many kilometers to the oasis. The underground design is critical, as it minimizes water loss to evaporation in the hyper-arid climate. At its peak, the system of tunnels stretched over 5,000 kilometers.
This reliable water supply allows for the cultivation of more than 100 varieties of grapes, making Turpan responsible for 90% of China's seedless grape crop. The intense heat and long hours of sunshine result in fruits with an exceptionally high sugar concentration. The region also has unique brick drying barns, which use the hot, dry winds to produce green raisins. The area was a key stop on the ancient Silk Road, with the ruins of the city of Gaochang demonstrating its historical importance. The basin also contains a fossil record, including dinosaur footprint fossils from the mid-Jurassic period, around 165 million years ago, and bones from massive sauropods.