Patagonian Desert - Geography and Climate

Geography and Climate

The Patagonian Desert is the largest continental landmass of the 40° parallel and is a large cold winter desert, where the temperature rarely exceeds 12°C and averages just 3°C. The region experiences about seven months of winter and five months of summer. Frost is not uncommon in the desert but, due to the very dry condition year round, snow is. The Andes, to the desert's west, are the primary reason for the Patagonian desert status as they inhibit the westerly flow of moisture from the southern Pacific from reaching inland. This creates a rain shadow that accounts for the formation of the desert and is why, despite approximately half of the desert being only about 200 miles from the ocean, such a large desert is found in the region. The cold Falkland Current off the Atlantic coast of South America also contributes to the area's aridity.

Different climates can be distinguished: the coast north of the 45th parallel is much milder because of the warm currents from Brazil, and the entire northern half of the region is significantly warmer in the summer, when sunny weather predominates. Daily temperatures in the summer reach 31°C in the Rio Colorado region, a general 26°C to 29°C in the northern coast, and 24°C to 28°C in the northern plain, with nights around 12°C to 15°C in the coast and between 7°C and 10°C in the steppe. In the south, summer temperatures decrease from 22°C to only 16°C along the coast, and from 24°C to 17°C along the steppes, while nights go from 8°C to 11°C on the coast, and from 6°C to 10°C in the steppe.

During the winter, the proximity to the coast and the altitude are the main factors: while northern coastal areas have mild winters, from 2°C at night to about 11°C during the day, southern Santa Cruz ranges from -2°C to 5°C, and Tierra del Fuego, from -3°C to 3°C, for a mean of 0°C. Inland, the northern areas range from 0°C to 10°C in low areas, and from -5°C to 5°C on the plateaus (again, mean around 0°C), while in the south, low areas range from -3°C to 4°C, and higher areas are clearly below 0°C. The coldest spots usually register temperatures between -20°C and -25°C during cold waves, and the official record is -33.9°C in Chubut province. However, some towns claim to have had records of around -35°C.

Summer frost is common everywhere except for the northern coast, and even sleet and light snow can fall during the warm season. Winds are constant and very strong, from the west in most cases.

Before the Andes were formed, the region was likely covered by temperate forests. However, after the formation of the Andes, ash from nearby volcanoes covered the forests and mineral-saturated waters seeped into the logs, thus fossilizing the trees and creating one of the world's best preserved petrified forests in the desert's center. The Patagonian is mainly composed of gravel plains and plateaus with sandstone canyons and clay shapes dotting the landscape, sculpted by the desert wind. The region encompassing the desert, however, has many diverse features. Ephemeral rivers, lakes, and drainage deposits from the Andes' spring melt form annually, hosting a variety of waterfowl and aquatic grasses. A variety of glacial, fluvial, and volcanic deposits are also found in the region and have significantly affected the desert's climate over time, especially contributing to the gravel sediments covering parts of the Patagonian.

The desert is quite windy as well, a result of the rain shadow effect and descending cool mountain air. This wind helps make the Patagonian one of the largest, if not the largest, sources of dust over the South Atlantic Ocean.

On the west the Patagonian grasslands portion of the Patagonian Desert are bounded by nothofagus forests of the Magellanic subpolar forests.

Volcanic rocks covers more than 120,000 km2 of the Patagonian Desert, mainly in the Somun Cura Massif (i.e. North Patagonian Massif) and the Deseado Massif. Some other volcanic areas include the Pali-Aike Volcanic Field near the Strait of Magellan. The volcanic rocks are the result of back-arc volcanism distributed mainly in two episodes: one in the Eocene and Miocene and the other from Late Miocene to Pleistocene.