The Time Has Come to Talk of Geology

Lago Ranco

How can sites of incredible beauty – massive snow-topped peaks, conical volcanoes, forest-bordered lakes, and ghostly thermal springs – also be connected to events of great tragedy? The answer lies in geology.

Zona Sur:

Chile’s Zona Sur (one of five distinct geographic zones) extends from the Bio-Bío River to the Gulf of Corcovado (just south of Chiloé island). Though this zone is further subdivided into three administrative regions — La Araucanía, historic center of the indigenous Mapuches; Los Ríos, region of rivers; and Los Lagos, of lakes — in reality, the entire area features an abundance of lakes, rivers, and Mapuche heritage.

Wikipedia image

Looking at a map, you detect a curious pattern. Some 15 lakes, interspersed with volcanoes and hot springs, form an almost straight line in the western foothills of the Andes mountains.

Why is that?

Long, long ago:

Cerro Tronador

Tectonic plates — vast sub-layers of the Earth’s crust — move, drift, and collide with the speed of a snail and the inevitability of death. Even before the plates disconnected South America from other continents (some 27 million years ago), the western Nazca plate began to slide under the eastern South America plate, and the colossal impacts (begun around 65 million years ago) have formed the Andean mountain range, longest in the world.

Long ago:

Osorno from Lago Todos los Santos

Beginning some two and a half million years ago, intervals of cold and warm temperatures caused the advance and retreat of glaciers and ice fields across the Patagonian landscape. After the end of the last glacial period, some 11,000 years ago, the lower extensions of glaciers retreated, leaving behind basins and u-shaped valleys. Accumulated glacial debris known as moraine blocked some of the basins, which then filled with melting glacial water. Voilà–lakes. In short, today’s lakes mark the western edge of much-larger glaciers that once blanketed the Andes. For more information about local geology, visit an article in Adventure Life.

Today:

Termas Geometricas

The same collision (subduction) of tectonic plates that lifted up the Andes eons ago remains at work today. Proof is in the volcanoes and hot springs found among the lakes of Zona Sur. Beneath the Earth’s crust where the plates collide, superheated liquid rock known as magma can build up pressure, eventually fracturing the rock above and spewing out hot lava, ashes, and gases. Zona Sur, the lake district, is Chile’s most active geothermal locale. Every year, visitors from around the world arrive here to view, and perhaps climb, its volcanoes and to soak in its hot springs.

Residents have long known the beauty of this region comes with a price – deadly volcanic eruptions and earthquakes so powerful they can annihilate cities. Few would trade it for anywhere else in the world.