EPOW - Ecology Picture of the Week

Glacial Valley of Enchantment

Valle Encantado (Enchanted Valley), Argentina

Explanation:  What formed this most enchanted valley, here in the Andes Mountains of southern Argentina along the border with Chile?  

It was fire, ice, sun, and seeds.  In that order. 

First came the fire of the Earth that built the Andes with massive upward volcanic force, layering the terrain with basaltic flows and pyroclastic strata of ash and rock.  Over the millennia, the strata tilted and jumbled and cracked, as the volcanoes vented and spewed.

Second came the ice in the form of alpine glaciers, that scraped and carved the valley into the classic U-shape form seen here.  Glaciers scoured raw the bedrock, slicing into the basaltic floor, creating typical alpine-glacial landforms of hanging side valleys and pinnacles and passes along the ridgelines.

Classic lateral moraine -- hills of ground rock material 
deposited by the melted glaciers, on which unique 
plant associations are found today.

Third came the sun, or warming climate to be more precise, that melted the ice.  The glaciers, no longer in force, deposited their massive loads of churned rubble and rock, leaving behind well-drained moraines and dropping huge boulders as "erratics" when the force of ice was no more.  Where once there were valley-filling glaciers now runs the Limay River.  

Then came the seeds of change, literally the seeds of pioneer plants brought by wind and animals, seeds stuck to the fur of guanacos and feathers of waterfowl.  Only the heartiest of plants, including the rock lichens, first sustained the harsh bare land in an initial flush of primary succession.  Later, protected by these pioneers, other plants invaded, the shrubs and low trees.  With vegetation also came occasional fires that scar the land but provide necessary conditions for the germination of some tree species that come to eventually dominate.  

And the story continues, with humans next to appear, who carved roads, planted exotic pine trees, brought in weeds and cattle and dogs and more people.  

But nature tends to cycle, and with climates shifting and volcanoes reborn, the cycle of this Enchanted Valley might reprise again.

Hanging valleys, left stranded after the glaciers carved their
pathways and then melted.

Tilted, warped, then carved by moving ice, these landforms are called
aretes (ridges and pinnnacles) and cols (the passes) -- 
classic forms of alpine glacial valleys.

A note on this location:

This is a wonderful, isolated valley -- actually called the Enchanted Valley -- south of the more popular and populous city of Bariloche, Argentina.  It is found past Lago Metiquina, Co. del Buque (with 1,952 meter-high peaks) and Co. Bayo (2,052 m), and the near non-existent settlement of Caleufu.  I visited here with botanist colleague and friend Andy MacKinnon as we explored the Andes.  

We came upon a South American red fox dashing across the road, being chased by a Crested Caracara (of the falcon family) as if the bird was chasing it from its territory, a most unusual sight.  The fox quickly ran into a bush thicket and disappeared from view.  

The Valley also held Common Diuca-Finches, guanacos, Andean Condors, and a variety of interesting plant species of the steppe vegetation, including ... Acaena sp. (a native, low shrub, with balls of seeds with spines or burrs, the seeds transported by passing guanacos and other mammals); Mutissia decurrens (a common steppe plant and focus of a previous EPOW episode); and naneo (Mulinum spinosum), a thorny branching plant with green stems and narrow leaves whose thorns likely evolved in defense against herbivorous mammals such as the guanaco.