Deep in the earth, beneath your feet, but less deep at Yellowstone National Park than in most places, the molten rock of the earth's interior transmits heat upward through sold rock to ground water which has penetrated to that depth. This extremely hot water then forces its way upward through fissures and fractures, warming rocks and water as it goes. Where the hot water can escape at the ground surface, a hot spring is formed.
Extremely hot water has properties important to the development of a hot spring's plumbing system. First, its lower density allows it to rise more easily through small channels. Second, it is a much better solvent than is cooler water; it dissolves astounding amounts of silica, a common component of volcanic rock. In this way, channels are enlarged while others are soon clogged with new deposits. The dissolved minerals are rapidly deposited around the hot springs and geysers as the water cools and can no longer hold it in solution.
Hot springs differ from geysers in that their underground systems allow rapid circulation of water. The rising hot water dissipates heat energy by evaporation or runoff, while convection currents return the cooler water to the underground system, keeping it in equilibrium.
This material is abstracted from brochures distributed by The Yellowstone Association for Natural Science, History & Education, Inc.
