Life at High Temperatures

by Thomas D. Brock

Kinds of Hot Springs

© 1994 Yellowstone Association for Natural Science, History & Education, Inc. Yellowstone National Park, Wyoming 82190.

Fountain Paint Pots Area

Each hot spring is unique. Even springs that look the same differ in characteristics such as temperature, flow rate, and chemistry of the water. One chemical property is so important that it has great influence on the kinds of organisms present: the acidity of the water. Some springs, such as those at Norris and Mud Volcano have very acid, sour-tasting water. They contain sulfuric acid, derived from the sulfur-rich gases emanating from the earth. Acid springs are usually concentrated in special basins, such as that of Sylvan Springs shown below, an important feature at the west end of Gibbon Meadow.

Most of the dominant thermal features in the Upper, Midway, and Lower Geyser Basins are not acid, however, but contain water that is neutral or weakly alkaline in character. An example is the large spring in the Fountain area, shown above.

The microorganisms in the acid springs are entirely different from those in the neutral to alkaline springs. Indeed, the organisms of acid hot springs have two environmental hurdles to overcome, high temperature and acidity. These organisms, called thermoacidophiles, are probably derived from some of the first organisms that arose on this planet.

pH of Yellowstone's Hot Springs

An expression called pH is used to denote the acidity or alkalinity of water. Water which is exactly neutral has a pH of 7. Acid waters have pH values below 7 and alkaline waters values above 7. Most acid springs in Yellowstone have pH values between 2 and 4, and the neutral/alkaline springs have values mostly from 7 to 9. The range of pH values for some Yellowstone hot springs and pools is shown on the scale below.

Sylvan Springs at the west end of Gibbon Meadow

Life at High Temperatures Table of Contents Previous Page Next Page