An Impossible Ecosystem
The Atacama Desert is the driest non-polar desert on Earth. Some areas receive less than a millimeter of rain per year, and certain riverbeds show evidence of being dry for 120,000 years. Yet, on the steep coastal mountainsides near Paposo, isolated pockets of dense vegetation thrive. These are the lomas, or fog oases, ecosystems that survive almost entirely without rain. Their existence depends on a persistent coastal fog, known locally as the camanchaca.
This dense fog is a product of the cold, north-flowing Humboldt ocean current. The cold water cools the air above it, causing moisture to condense into a thick stratocumulus cloud bank that rolls inland. While the water droplets in the fog, measuring just 1 to 40 microns in diameter, are too small to fall as rain, they provide life-giving water through a process of direct condensation. As the fog moves through the vegetation, droplets collect on the surfaces of leaves, stems, and lichens, a phenomenon called horizontal precipitation. This process is most effective at altitudes between 300 and 1,000 meters, creating distinct bands of green on the otherwise barren hills.