Repeat Photography by Robert H. Webb

Author:Robert H. Webb [Webb, Robert H.]
Language: eng
Format: epub
ISBN: 9781610910064
Publisher: Island Press
Published: 2012-09-12T05:00:00+00:00

Setting

The areas of interest to this chapter are the Lake District (ca. 39–42° S) of south-central Chile and northwestern Patagonia, Argentina (ca. 39–43° S; fig. 13.1). At about 39° S along a west-to-east transect, the physiography consists of the Coastal Cordillera and the Central Depression in Chile, the Andes, and the Patagonian Plains in Argentina (Veblen 2007). On both the Chilean and Argentine sides of the Andes, Quaternary glaciers scoured large lakes in the Andean foothills. Northward of about 43° S on the Chilean side, the Andes are paralleled by the Coastal Cordillera that rarely exceed 1,000 meters in elevation. The two mountain systems are separated by an intervening Central Depression of structural origin that is filled with Quaternary glacial, fluvioglacial, aeolian, and alluvial deposits and volcanic ash. South of about 43° S, the Andes rise directly from a coastal maze of islands and steep fiords. East of the Andean summits are the precordilleran foothills and the vast Patagonian Plains.

The dominant climate mechanisms of the southern Andes are the persistent midlatitude westerlies, the seasonally shifting subtropical anticyclone of the southeastern Pacific region, and the topographic influences of the coastal and Andean mountains (Veblen 2007). Orographic uplift of the westerly airflow results in mean annual precipitations of 3,000 to over 5,000 millimeters on the windward slopes of mountains from 40° S southward. At higher elevations (e.g., above 900 meters at 40° S), winter precipitation is mostly in the form of snow. The Andes produce a strong precipitation shadow to their lee; for example, over a west-to-east distance of only 50 kilometers at about 40° S, mean annual precipitation declines from greater than 3,000 millimeters to less than 800 millimeters.

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