An ancient reservoir beneath the salt
The Pampa del Tamarugal is a plateau within the Atacama Desert, the driest non-polar desert on Earth. Some areas receive less than 2 millimeters of rain per year, and geological evidence suggests parts of the desert have been hyperarid for millions of years. Beneath the salt-encrusted surface lies a vast, silent resource: the Pampa del Tamarugal Aquifer. This is not a river that flows, but a massive underground body of water held in gravel and sand.
The water in this aquifer is "fossil water." Isotope dating techniques, which measure the decay of elements like tritium or carbon-14, show that much of this water is thousands of years old. It last fell as rain during the Pleistocene epoch, a time when the climate was wetter and precipitation from the Andes mountains regularly flowed down to recharge the basin. Today, with near-zero local rainfall, the aquifer receives almost no replenishment. It is a finite resource from a different geological age. The water table lies at depths between 2 and 40 meters below the surface.
The tree that drinks ancient water
This ancient water is the sole reason for the existence of one of the world's most peculiar forests. The tamarugo tree, Prosopis tamarugo, forms woodlands in the middle of this hyperarid landscape, protected within the Pampa del Tamarugal National Reserve. These trees are phreatophytes, which depend on groundwater. To reach the fossil water, the tamarugo has a specialized dual root system. A deep taproot can penetrate up to 15 meters underground to reach the capillary fringe above the water table. A separate, dense network of shallow roots spreads out near the surface.
This adaptation allows a tree that can grow up to 18 meters tall to thrive where virtually no other trees can survive. The entire ecosystem of the Pampa del Tamarugal—from the insects that pollinate the tamarugo's yellow flowers to the Darwin's leaf-eared mouse (Phyllotis darwini)—depends on this species' ability to tap a prehistoric water source.
The aquifer and the life it supports now face a modern threat. The Atacama region has copper and lithium deposits, and large-scale mining is a water-intensive industry. To supply their operations, mining companies pump enormous quantities of water directly from the aquifer. Over the last three decades, water usage from the Pampa del Tamarugal aquifer has increased by approximately 1,900%. This rate of extraction far exceeds the negligible rate of natural recharge, causing water table levels to drop and placing the unique tamarugo forests under severe stress.