A Sour World: Life and Death at Low pH

Abstract

I discussed the origin of acidic environments in Chapter 1. As noted, a solfatara is a location where elemental sulfur is precipitating out, due to surficial oxidation of H₂S rising with steam from within the earth. Solfataras are generally areas with minimum amounts of ground water, and the circulation of water through the habitat is very shallow. Thus, except for the acidity and high-sulfate content, the chemistry of acidic geothermal waters is often closer to normal ground water than to deep geothermal water. A typical solfatara, Roaring Mountain, is shown in Figure 12.1a and an acid lake associated with another solfatara is shown in Figure 12.1b. Many solfataras are characterized by crumbling rock, hollow ground, and bleached color, due to acid attack on the rock-forming minerals and to leaching of color-forming components such as iron. The rate at which rocks disintegrate in solfatara areas is amazingly high. During the 10 years that I was in Yellowstone, I actually watched several large rocks disintegrate, and the boulder shown in Figure 12.2a, about the size of an automobile, split into two and collapsed. The power of acid is even more dramatically illustrated by the Grand Canyon of the Yellowstone River (Figure 12.2b), which is riddled with solfataric ground in the area where it is the deepest.