Chemical Precipitation in the Rocky Mountains

September 18, 2012

DeerCreekSnakeRiver (2)

Photographer: Thomas McGuire
Summary Author: Thomas McGuire

September 2012 Viewer's Choice In high school chemistry, you may have watched a mixture of dissolved chemicals in a test tube produce a dramatically colored precipitate. Such rapid chemical reactions are not common in nature. But this is exactly what occurs when Deer Creek meets the upper Snake River near the Continental Divide, about 40 mi (64 km) west of Denver, Colorado. At the confluence (image on the left), the fledgling Snake River is naturally acidic (low pH) with high concentrations of dissolved aluminum and iron ions. Note that iron precipitation gives the streambed a rusty brown color. Deer Creek, on the other hand, is naturally basic (high pH) and appears colorless. The mixing of the streams reduces the acidity of the water, leading to precipitation of oxides of iron and aluminum. A few hundred yards below the confluence (right image), aluminum oxide causes the stream to appear a pale white to milky blue color. Photos taken in September 2005.

Photo Details: Camera: Konica DiMAGE A2; Focal Length: 11.1mm (35mm equivalent: 43mm); Aperture: f/5.6; Exposure Time: 0.017 s (1/60); ISO equiv: 64; Software: Adobe Photoshop Elements 9.0 Macintosh.