Geothermal areas of Yellowstone
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The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs, mud pots and fumaroles. In total, the number of thermal features in Yellowstone is estimated at 10,000Geothermal Features and How They Work and 200 to 250 geysers erupt in Yellowstone each year, making it the the place with the highest concentration of active geysers in the world.Windows into the Earth, page 73 Many of these features build up sinter, geyserite or travertine deposits around and within them.
The various geyser basins are located where rainwater and snowmelt can easily percolate into the ground, get indirectly superheated by the underlying Yellowstone hotspot, and then easily erupt at the surface as geysers, hot springs, and fumaroles. Thus flat-bottomed valleys between ancient lava flows and glacial moraines are where most of the large geothermal areas are located. Smaller geothermal areas can be found where fault lines reach the surface, in places along the circular fracture zone around the caldera and at the base of slopes that collect excess groundwater. Due to high elevation of the Yellowstone Plateau, the average boiling temperature at Yellowstone's geyser basins is 199 °F (93 °C). When properly confined and close to the surface it can periodically release some of the built-up pressure in eruptions of hot water and steam that can reach up to 390 feet (120 m) into the air (see Steamboat Geyser, the world’s tallest geyser).Windows into the Earth, page 79 Water erupting from Yellowstone's geysers is superheated above that boiling point to an average of 204 °F (95.5 °C) as it leaves the vent. The water cools significantly while airborne and is no longer scalding hot by the time it strikes the ground, nearby boardwalks, or even spectators. However, because of the high temperatures of the water in the features, it is important that spectators remain on the boardwalks and designated trails. Several deaths have occurred in the park as a result of falls into hot springs.
Prehistoric Native American artifacts has been found at Mammoth Hot Springs and other geothermal areas in Yellowstone. Some accounts state that they used hot water from the geothermal features for bathing and cooking. In the 19th century, Father Pierre-Jean De Smet reported that natives he interviewed thought that geyser eruptions were "the result of combat between the infernal spirits."Windows into the Earth, page 70 The Lewis and Clarke Expedition traveled north of the Yellowstone area in 1806. Local natives that they came upon seldom dared to enter what we now know is the caldera because of frequent loud noises that sounded like thunder and the belief that the spirits that possessed the area did not like human intrusion into their realm.Windows into the Earth, page 71 The first Caucasian known to travel into the caldera and see the geothermal features was John Colter, who had left the Lewis and Clarke Expedition. He described what he saw as "hot spring brimstone." Beaver trapper Joseph Meek recounted in 1830 that the steam rising from the various geyser basins reminded him of smoke coming from industrial stacks on a cold winter morning in Pittsburgh, Pennsylvania. In the 1850s, famed trapper Jim Bridger called it "the place where Hell bubbled up.".
Types of features found in the park
The heat that drives geothermal activity in the Yellowstone area comes from a brine (salty water) that is 1.5 to 3 miles (2.4 to 4.8 km) below the surface. This is actually below the solid volcanic rock and sediment that extends to a depth of 3,000 to 6,000 feet (900 to 1800 m) and is inside the hot but mostly solid part of the pluton that contains Yellowstone’s magma chamber.Windows into the Earth", page 69 At that depth the brine is superheated to temperatures that exceed 400° F (double the boiling point at the surface) but is able to remain a liquid because it is under great pressure (not unlike a huge pressure cooker).Yellowstone Resources and Issues: 2006'', page 41Convection of the churning brine and conduction from surrounding rock transfers heat to an overlaying layer of fresh groundwater. Movement of the two liquids is facilitated by the highly fractured and porous nature of the rocks under the Yellowstone Plateau. Some silica is dissolved from the fractured rhyolite into the hot water as it travels through the fractured rock. Part of this hard mineral is later redeposited on the walls of the cracks and fissures to make a nearly pressure-tight system. At the surface, silica precipitates to form either geyserite or sinter, creating the massive geyser cones, the scalloped edges of hot springs, and the seemingly barren landscape of geyser basins.
Geysers are a type of geothermal feature that erupt scalding hot water. Increased pressure exerted by the enormous weight of the overlying rock and water prevents deeper water from boiling. As the hot water rises it is under less pressure and steam bubbles form. They, in turn, expand on their ascent until the bubbles are too big and numerous to pass freely through constrictions. At a critical point, the confined bubbles actually lift the water above, causing the geyser to splash or overflow. This decrease the pressure of the system and violet boiling results. Large quantities of water flash into tremendous amounts of steam that force a jet of water out of the vent; an eruption begins. Water and heat is expelled faster than the geyser’s recharge rate, gradually decreasing the system’s pressure and eventually ending the eruption.
Hot springs such as Grand Prismatic Spring are the most common hydrothermal features in the park. Their plumbing has no constrictions. Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below. This circulation, called convection, prevents water from reaching the temperature needed to set off an eruption.
Mudpots such as Fountain Paint Pot are acidic hot springs with a limited water supply. Some microorganisms use hydrogen sulfide (rotten egg smell), which rises from deep within the earth, as an energy source. They convert the gas into sulfuric acid, which breaks down rock into clay.
Fumaroles or steam vents, are the hottest hydrothermal features in the park. They have so little water that it all flashes into steam before reaching the surface. At places like Roaring Mountain, the result is loud hissing of steam and gases.
Travertine terraces, found at Mammoth Hot Springs, are formed from limestone (a rock type made of calcium carbonate) Thermal waters rise through the limestone, carrying high amounts of dissolved carbonate. At the surface, carbon dioxide is released and calcium carbonate is deposited as travertine, the chalky white rock of the terraces. Due to the rapid rate of deposition, these features constantly and quickly change.
Geyser Basins
Norris Geyser Basin
Norris Geyser Basin is the hottest geyser basin in the parkNorris Geyser Basin Tour and is located near the northwest edge of Yellowstone Caldera near Norris Junction and on the intersection of three major faults. The Norris-Mammoth Corridor is a fault that runs from Norris north through Mammoth to the Gardiner, Montana, area. The Hebgen Lake fault runs from northwest of West Yellowstone, Montana, to Norris. This fault experienced an earthquake in 1959 that measured 7.4 on the Richter scale (sources vary on exact magnitude between 7.1 and 7.8). These two faults intersect with a ring fracture that resulted from the Yellowstone Caldera of 630,000 years ago. These faults are the primary reason that Norris Geyser Basin is so hot and dynamic.Geological Overview of the Norris Area
Unlike most of other geyser basins in the park, the waters from Norris are acidicNatural Highlights of the Norris Area rather than alkaline. The difference in pH allows for a different class of bacterial thermophiles to live at Norris, creating different color patterns in and around the Norris Basin waters.
The tallest active geyser in the world is Steamboat GeyserGeological Overview of the Norris Area and it is located in Norris Basin. Unlike the slightly smaller but much more famous Old Faithful Geyser located in Upper Geyser Basin, Steamboat has an erratic and lengthy timetable between major eruptions. During major eruptions, which may be separated by intervals of more than a year (the longest span between major eruptions was 50 years), Steamboat erupts over 300 feet (90 m) into the air. However, Steamboat does not lie dormant between eruptions, instead displaying minor eruptions of approximately 40 feet (12 m).
The Ragged Hills that lie between Back Basin and One Hundred Springs Plain are thermally altered glacial moraines. As glaciers receded, the underlying thermal features began to express themselves once again, melting remnants of the ice and causing masses of debris to be dumped. These debris piles were then altered by steam and hot water flowing through them. Madison lies within the eroded stream channels cut through lava flows formed after the caldera eruption. The Gibbon Falls lies on the caldera boundary as does Virginia Cascades.Norris Geyser Basin Tour
Upper Geyser Basin
South of Norris along the rim of the caldera is the Upper Geyser Basin, which has the highest concentration of geothermal features in the park. This complement of features includes the most famous geyser in the park, Old Faithful Geyser, as well as four other predictable large geysers. One of these large geysers in the area is Castle Geyser which is about 1400 feet northwest of Old Faithful. Castle Geyser has an interval of approximately 13 hours between major eruptions, but is unpredictable after minor eruptions. The other three predictable geysers are Grand Geyser, Daisy Geyser, and Riverside Geyser.
The hills surrounding Old Faithful and the Upper Geyser Basin are reminders of Quaternary rhyolitic lava flows. These flows, occurring long after the catastrophic eruption of 600,000 years ago, flowed across the landscape like stiff mounds of bread dough due to their high silica content.
Evidence of glacial activity is common, and it is one of the keys that allows geysers to exist. Glacier till deposits underlie the geyser basins providing storage areas for the water used in eruptions. Many landforms, such as Porcupine Hills north of Fountain Flats, are comprised of glacial gravel and are reminders that as recently as 13,000 years ago, this area was buried under ice.
Signs of the forces of erosion can be seen everywhere, from runoff channels carved across the sinter in the geyser basins to the drainage created by the Firehole River. Mountain building is evident on the drive south of Old Faithful, toward Craig Pass. Here the Rocky Mountains reach a height of 8,262 feet (2518 m), dividing the country into two distinct watersheds.Geological Overview of the Old Faithful Area
Midway Geyser Basin
This basin is much smaller than the other basins found alongside the Firehole River. Despite its small size, this basin contains two large features, the Excelsior Geyser which pours over 4,000 gallons (15,000 liter) per minute into the Firehole River. The largest hot spring in Yellowstone, the Grand Prismatic Spring is also found here.Natural Highlights of the Old Faithful Area
Lower Geyser Basin
Further south is the Lower Geyser Basin, which has a much less concentrated set of geothermal features, including Fountain Paint Pots. Fountain Paint Pots are mud pots, that is, a hot spring that contains boiling mud instead of water. The mud is produced by a higher acidity in the water which enables the spring to dissolve surrounding minerals to create an opaque, usually grey, mud.
West Thumb Geyser Basin
The West Thumb Geyser Basin, including Potts Basin to the north, is unique in that it is the largest geyser basin on the shores of Yellowstone Lake. The heat source of the thermal features in this location is thought to be relatively close to the surface, only 10,000 feet (3000 m) down. The West Thumb of Yellowstone Lake was formed by a large volcanic explosion that occurred approximately 150,000 years ago (125,000-200,000). The resulting caldera later filled with water forming an extension of Yellowstone Lake. The West Thumb is about the same size as another famous volcanic caldera, Crater Lake in Oregon, but much smaller than the great Yellowstone Caldera which formed 600,000 years ago. It is interesting to note that West Thumb is a caldera within a caldera.Ring fractures formed as the magma chamber bulged up under the surface of the earth and subsequently cracked, releasing the enclosed magma. This created the source of heat for the West Thumb Geyser Basin today.
The thermal features at West Thumb are found not only on the lake shore, but extend under the surface of the lake as well. Several underwater geysers were discovered in the early 1990s and can be seen as slick spots or slight bulges in the summer. During the winter, the underwater thermal features are visible as melt holes in the icy surface of the lake. The ice averages about three feet thick during the winter.Geological Overview of the Grant Village & West Thumb Areas
Backcountry Geyser Basins
The Gibbon, Heart Lake, Lone Star, and Shoshone Geyser Basins are located away from the heavily traveled portions of the park. Some require several miles of off-trail hiking to reach. These areas also generally lack the boardwalks and other safety features of the developed areas. As falling into geothermal features can be fatal, it is usually advisable to visit these areas with an experienced guide or at the very least, travelers need to ensure they remain on well marked trails.
Hot Springs Basin is is located 15 miles (24 km) north-northeast of Fishing Bridge and has one of Yellowstone's largest collections of hot springs and fumaroles.For the whole paragraph, except where noted: Windows into the Earth, page 73, paragraph 5 The geothermal features there release large amounts of sulpher. This makes water from the springs so acidic that it has disolved holes in the pants of people who sit on wet ground and causes causes monds of sulpher three feet (1 m) high to develop around fumaroles. The very hot acidic water and steam has also created easily exposed hollows in the ground that are only covered by a thin crust.
Mammoth Hot Springs
In the northwest corner of the park there is a large hot spring complex near Fort Yellowstone called Mammoth Hot Springs. Mammoth is a large hill of travertine that has been created over thousands of years as hot water from the spring cooled and deposited calcium carbonate (over 2 tons of calcium carbonate flows into Mammoth each day in a solution). Although these springs lie outside the caldera boundary, their energy is attributed to the same magmatic system that fuels other Yellowstone geothermal areas.
The hot water that feeds Mammoth comes from Norris Geyser Basin after traveling underground via a fault lineMammoth Hot Springs Tour Home that runs through limestone and roughly with the Norris to Mammoth road (the limestone is the source of the calcium carbonate). Shallow circulation along this corridor allows Norris' super-heated water to cool somewhat before surfacing at Mammoth, generally at about 170° F (~77° C). Algae living in the warm pools have tinted that travertine shades of brown, orange, red and green.
Thermal activity here is extensive both over time and distance. Terrace Mountain at Mammoth Hot Springs is the largest known carbonate-depositing spring in the world. The most famous feature at the springs is the Minerva Terrace, a series of travertine terraces. The terraces have been deposited by the spring over many years, but due to recent minor earthquake activity, the spring vent has shifted, rendering the terraces dry.
The Mammoth Terraces extend all the way from the hillside, across the Parade Ground, and down to Boiling River. The Mammoth Hotel, as well as all of Fort Yellowstone, is built upon an old terrace formation known as Hotel Terrace. There was some concern when construction began in 1891 on the Fort site that the hollow ground would not support the weight of the buildings. Several large sink holes (fenced off) can be seen out on the Parade Ground. This area has been thermally active for several thousand years.
The Mammoth area exhibits much evidence of glacial activity from the Pinedale Glaciation. The summit of Terrace Mountain is covered with glacial till, thereby dating the travertine formation there to earlier than the end of the Pinedale Glaciation. Several thermal kames, including Capitol Hill and Dude Hill, are major features of the Mammoth Village area. Ice-marginal stream beds are in evidence in the small, narrow valleys where Floating Island Lake and Phantom Lake are found. In Gardner Canyon, one can see the old, sorted gravel bed of the Gardner River covered by unsorted glacial till.
Mud Volcano and Sulphur Caldron
The thermal features at Mud Volcano and Sulphur Caldron are primarily mud pots and fumaroles because the area is situated on a parched water system with little water available. Fumaroles or "steam vents" occur when the ground water boils away faster than it can be recharged. Also, the vapors are rich in sulfuric acid that leaches the rock, breaking it down into clay. Because no water washes away the acid or leached rock, it remains as sticky clay to form a mud pot. Hydrogen sulfide gas is present deep in the earth at Mud Volcano. As this gas combines with water and the sulfur is metabolized by cyanobacteria, a solution of sulfuric acid is formed that dissolves the surface soils to create pools and cones of clay and mud. Along with hydrogen sulfide, steam, carbon dioxide, and other gases explode through the layers of mud.
A series of shallow earthquakes associated with the volcanic activity in Yellowstone struck this area in 1978. Soil temperatures increased to nearly 200° F (93° C). The slope between Sizzling Basin and Mud Geyser, once covered with green grass and trees, became a barren landscape of fallen trees known as "the cooking hillside."
See also
References
Works cited
- Bryan, T. Scott (1995). The geysers of Yellowstone. Niwot, Colorado: University Press of Colorado. ISBN 087081365X
- Harris, Ann G.; Tuttle, Esther; and Tuttle, Sherwood D. (1995). Geology of national parks: fifth edition. Iowa: Kendall/Hunt Publishing. ISBN 0-7872-5353-7
- [National Park Service - Geological Overview of Specific Yellowstone National Park Areas]
Notes
External links
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