The central Andean west‐slope rainshadow and its potential contribution to the origin of hyper‐aridity in the Atacama Desert

Abstract

The west slope of the central Andes exhibits a pronounced rainshadow effect. Precipitation between 15°and 27°S is dominated by summer convective activity from Amazonia, and data analysis shows that the increase in precipitation with elevation due to the rainshadow effect best fits an exponential correlation. Coupling with limited data from high elevations suggests that the correlation is accurate to 4500 m above sea level (m a.s.l.) and perhaps to 5500 m a.s.l., suggesting that increased precipitation goes unrecorded over the peaks of the western Cordillera. South of 27°S the precipitation is dominated by winter frontal sources and shows no well-defined relationship with elevation. The core zone of hyper-aridity in the Atacama Desert extends from 15 to 30°S at elevations from sea level to 3500 m a.s.l. Although the Atacama Desert has existed since at least 90 Ma, it is considered that the initial onset of hyper-aridity was most likely to have developed progressively with the uplift of the Andes as they reached elevations between 1000 to 2000 m a.s.l. coupled with the intensification of a cold, upwelling Peruvian Current between 15 and 10 Ma. Also apparent in the palaeogeographic record are subsequent fluctuations between (semi-) arid to hyper-arid conditions that were probably largely controlled by changes in orbital and oceanic forcing.

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

“…Repeated onset of hyperaridity since 14 Ma may be further responsible for ambiguous records and interpretations (Jordan et al, 2014). These transitions have been tied to (1) a coastal temperature inversion from the cold Humboldt current formed concurrent with the opening of the Drake Passage (Gregory‐Wodzicki, 2000; Lawver & Gahagan, 1998; Wörner et al, 2002), (2) an Andean rain shadow blocking off Atlantic moisture as a result of post‐Miocene uplift (e.g., Houston & Hartley, 2003; Rech et al, 2006, 2010), and (3) additional shut off from Pacific moisture blocked by the Coastal Cordillera(Rech et al, 2010). Present‐day precipitation rates are recorded as low as <1 mm/yr in the coastal cities of northern Chile (e.g., Schulz et al, 2012).…”

Prospecting Glacial Ages and Paleoclimatic Reconstructions Northeastward of Nevado Coropuna (16° S, 73° W, 6377 m), Arid Tropical Andes

“…The coast of southern Peru and northern Chile is the most arid region on Earth (annual precipitation <20 mm) as a result of three main causes [52][53][54]: (1) The Andes represent a major topographic barrier to atmospheric circulation in South America; (2) A temperature inversion layer over the Pacific Ocean (700-1000 m) due to the Humboldt cold-water current and (3) Large-scale tropospheric subsidence.…”

Origin and development of theater-headed valleys in the Atacama Desert, northern Chile: Morphological analogs to martian valley networks

“…The Atacama Desert is extremely dry due to a combination of topography, atmospheric circulation, and ocean currents (e.g., Houston and Hartley, 2003). The descending Hadley circulation and easterly winds at this latitude ($20°S) combine with continentality and the Andean rain shadow to inhibit precipitation.…”

“…The cold Humboldt Current runs northward along the Pacific coast, cooling the near-surface air and creating a stable temperature profile, so moist air is trapped along the coast. In northern Chile, the annual precipitation and resulting fluvial dissection decline rapidly westward, with annual rainfall ranging from $20 cm/a at higher elevations to <0.1 cm/a near the coast (Houston and Hartley, 2003;Houston, 2006;Strecker et al, 2007;García et al, 2011). Long-term semiarid to hyperarid climates, arguably since the late Triassic (Clarke, 2006) or late Jurassic (Hartley et al, 2005), has combined with rapid uplift of the Andes since the Miocene (when the rain shadow and aridity were enhanced) to create a landscape in which tectonic features are unusually well expressed on the surface (Gregory-Wodzicki, 2000;Rech et al, 2006).…”