Groundwater Features: Geysers of Yellowstone National Park
The groundwater feature that is analyzed in this essay is the geysers of Yellowstone National Park. The Yellowstone National Park is located primarily in the state of Wyoming, with some small areas in neighboring states of Idaho and Montana in the United States of America.
A geyser is a type of hot spring that erupts periodically, discharging a column hot water and steam up into the air. Geysers are found only in regions of volcanic activity and are connected to masses of siliceous lava. Geysers usually have a narrow vent at the surface that is connected to the groundwater chamber through one or more narrow tubes, which form the plumbing of the geysers. The groundwater gets heated up by underlying rocks that in turn get conducted heat from the magma. This geothermally heated water gets constricted by the non-porous inner walls of a geyser and is trapped under layers of cooler water blocking the vents. The high pressure prevents ebullition and superheated temperatures are reached. Gradually, the upper layers that are not under pressure get hot enough for boiling. The steam pushes through the vents, displacing the topmost layers of water and thereby releasing the pressure on the lower superheated layers. The superheated water then gushes out and a part of it gets converted into steam. This causes the violent eruption of a geyser. Once this eruption is over, the residual water cools down below boiling point, the heated groundwater seeps back into the reservoir and the cycle begins again (Hobbs,1931).
Yellowstone contains more than 300 geysers, about two thirds of the total found on earth. The geysers of Yellowstone were created by the volcanic activity of Yellowstone Caldera, the largest volcanic system in entire North America. The current Caldera was formed 640,000 years ago by a massive eruption that released more than a thousand cubic Km of rock, ash and pyroclastic materials. This was followed by a couple of smaller eruptive cycles, the last one ending 70, 000 years ago. The caldera was nearly filled with rhyolitic and basaltic lava flows due to these eruptions. The rhyolitic flow was very viscous and the rhyolite silica rich, acidic and water soluble in nature. Parts of this rhyolitic deposits got dissolved in hot water to form siliceous sinter or geyserite deposits on the inside walls of the geyser plumbing. With time, these deposits accumulated, strengthening the plumbing walls and providing stability to the geyser. At Yellowstone, the magma lies only 6 Km below the surface. The groundwater attains temperatures of 200o C at depths of 200m. These are ideal conditions for geyser activities. Each geyser here has developed its own typical pattern of duration, height and interval of eruption depending upon its water supply, fissures and internal structure (Scarth, 1994). Yellowstone abounds in both cone geysers like the Old Faithful, where the jet of water erupts out of a small vent in a geyserite mound and fountain geysers like the Cistern Spring, that erupts violently from a pool with a relatively larger vent.
The geysers of Yellowstone National Park have been a major tourist attraction and it remains the only undisturbed geyser basin in the world. Geothermal energy harvesting, which has obliterated many geysers in Iceland and New Zealand, has not been allowed here. The geysers of Yellowstone have been researched by geophysicists for geothermal activities and by biologists for thermophilic bacteria, algae mats and predators (NPS, US Govt.).
The future of Yellowstone geysers depends upon both the natural volcanic and seismic activities in that zone and the effectiveness of controls placed on adverse human activities. The presence of water, sewer and other utilities and construction activities nearby can have disastrous impact on them. Changing energy economics may force opening up of non-federal land to geothermal drilling activities. The 1994 Water Rights Compact agreement between the state of Montana and the National Park Service that prevents adverse impact of groundwater usage on the geothermal features can serve as a future model for conservation (NPS, US Govt.).
Hobbs, W.H. (1931). Earth Features and Their Meaning. New York, Macmillan Company.
National Park Service, U.S. Department of the Interior. Yellowstone National Park.
Scrath, A. (1994). Volcanoes: An Introduction London, UCL Press.