Red Creeks in the Western Alps
February 09, 2015
Walking in the beautiful Thur River Valley in the Western Italian Alps, close to France, you can't miss noticing the intense brownish red colors of a few of the creeks. On these mountains, rain infiltrates in the subsoil and runs through permeable rocks. At first, the water follows a winding route downward, then it's pushed to the surface by the pressure. When running through the subsoil, water transforms the rocks and enriches itself with compounds such as calcium sulfate (gypsum) and iron minerals that are available in large quantities. Rising to the surface, this spring water loses its iron as oxides and hydroxides, hence the eye-catching red color.
High concentrations of calcium sulfate allow the re-crystallization of gypsum (the small crystals on the rocks in the bottom photo). Both photos taken on November 24, 2014.