Yellowstone hot spot
The northwest corner of Wyoming and adjacent parts of Idaho and Montana were established as Yellowstone National Park in 1872 by President Ulysses S. Grant, and it remains the largest national park in the conterminous united States. The park serves as a large nature preserve and has large populations of moose, bear, sheep, elk, bison, numerous birds, and a diverse flora. The park sits on a large upland plateau resting at about 8,000 feet (2,400 m) elevation straddling the continental divide. The plateau is surrounded by mountains that range from 10,000 to 14,000 feet (3,000-4,250 m) above sea level. Most of the rocks in the park formed from a massive volcanic eruption that occurred 600,000 years ago, forming a collapse caldera 28 miles (45 km) wide and 46 miles (74 km) long. Yellowstone Lake now largely occupies the deepest part of the caldera. The region is still underlain by molten magma that heats the groundwater system, which boasts more than 10,000 hot springs, 200 geysers, and numerous steaming fumaroles, and hot mud pools. The most famous geyser in the park is Old Faithful, which erupts an average of once every 64.5 minutes blowing 11,000 gallons (41,500 L) of water 150 feet (46 m) into the air. The most famous hot springs include Mammoth hot springs, on the northern side of the park, where giant travertine and mineral terraces have formed from the spring, and where simple heat-loving (ther-mophilic) organisms live in the hot waters. other remarkable features of the park include the petrified forests buried and preserved by the volcanic ash, numerous volcanic formations including black obsidian cliff, and waterfalls and canyons including the spectacular Lower Falls in the Grand Canyon of the Yellowstone.
The massive eruption from Yellowstone caldera 600,000 years ago covered huge amounts of the western United States with volcanic ash. If such an eruption were to occur today, the results would be devastating, with perhaps 20 percent of the lower united states covered with thick, hardened ash and burning fumes extending across the whole country. There has been some concern recently about an increase in some of the thermal activity in Yellowstone, although it is probably related to normal changes within the complex system of heated ground-water and seasonal or longer changes in the ground-water system. First, steamboat geyser, which had been quiet for two decades, began erupting in 2002. New lines of fumaroles formed around Nymph Lake, including one line 250 feet long (75 m) that forced the closure of the visitor trail around the geyser basin. other geysers, have seen temperature increases from 152°F (67°C) to 190°F (88°C) over a several-month period. other changes include a greater discharge of steam from some geysers, changes in the frequency of eruptions, and a greater turbidity of thermal pools. Perhaps most worrisome is the discovery of a large bulge beneath Yellowstone Lake, although its age and origin are uncertain. Fears are that the bulge may be related to the emplacement of magma to shallow crustal levels, a process that sometimes precedes eruptions. But the bulge was recently discovered because new techniques are being used to map the lake bottom. The feature has an unknown age and may have been there for decades to hundreds of years.
Yellowstone Park is underlain by a hot spot, the surface expression of a mantle plume. As the
North American plate has migrated 280 miles (450 km) southwestward with respect to this hot spot in the past 16 million years, the volcanic effects migrated from the Snake River Plain to the Yellowstone Plateau. There is currently a parabolic-shaped area of seismicity, active faulting, and centers of igneous intrusion centered around the parabolic area, all of which are migrating northeastward. Heat and magma from this mantle plume has emplaced as much as 7.5 miles (12 km) of mafic magma into the continental crust over the plume along this trace, causing the surface eruptions of the massive Snake River Plain flood basalts, and the Yellowstone volca-nics. on geological timescales massive volcanism and other effects of this hot spot will likely continue and also slowly move northeast.
See also convection and the Earth's mantle; energy in the earth system; volcano.
Fisher, R. V. Out of the Crater: Chronicles of a Volcanolo-gist. Princeton, N.J.: Princeton University Press, 2000. Francis, Peter. Volcanoes: A Planetary Perspective. Oxford:
Oxford University Press, 1993. Hawaiian Volcano Observatory. Available online. URL: http://hvo.wr.usgs.gov/. Accessed November 2, 2008. MacDougall, J. D., ed. Continental Flood Basalts. Dordrecht, Germany: Kluwer Academic Publishers, 1988. Mahoney, J. J., and M. F. Coffin, eds. Large Igneous Provinces, Continental, Oceanic, and Planetary Flood Volcanism. Washington, D.C.: American Geophysical Union, 1997.
Morgan, Lisa A., David J. Doherty, and William P. Leeman. "Ignimbrites of the Eastern Snake River Plain: Evidence for Major Caldera Forming Eruptions." Journal of Geophysical Research 89 (1984): 8,665-8,678. Morgan, W. Jason. "Deep Mantle Convection Plume and Plate Motions." American Association of Petroleum Geologists Bulletin 56 (1972): 202-213. Rogers, David W., R. William Hackett, and H. Thomas Ore. "Extension of the Yellowstone Plateau, Eastern Snake River Plain, and Owyhee Plateau." Geology 18 (1990): 1,138-1,141. Volcanoworld. Available online. URL: http://volcano.und. edu/. Accessed August 27, 2006.
Hubble, Edwin (1889-1953) American Astronomer Edwin Powell Hubble was born on November 20, 1889, in Marshfield, Missouri, but his family moved to Wheaton, Illinois, the same year. In his career Hubble made two important discoveries that changed scientists' understanding of the universe. He was the first to prove the existence of galaxies beyond the Milky Way, and he discovered that the redshift of galaxies increased with their distance from the Milky
Way, showing that the universe is expanding in all directions.
Hubble performed well in grade and high school but paid more attention to sports than academics. He completed a bachelor of science degree at the University of Chicago in 1910, with concentrations in mathematics, astronomy, and philosophy. From 1910 to 1913 Hubble was a Rhodes Scholar at Oxford, England, where he studied jurisprudence and spanish, then returned to the united states. He was inducted into the Kentucky bar association though he never practiced law. Instead he taught high school and became a basketball coach, until he served in World War I. After the war Hubble returned to astronomy studies at the Yerkes Observatory at the University of Chicago, earning a Ph.D. in 1917 for his dissertation, "Photographic Investigations of Faint Nebula." In 1919 Hubble took a position at the Mount Wilson Observatory near Pasadena, California, where he was the first person to use Palomar's 200-inch Hale Telescope. Edwin Hubble died suddenly on September 28, 1953, of a cerebral thrombosis.
When Hubble arrived at the Mount Wilson observatory in 1919, astronomers believed that the universe did not extend beyond the Milky Way, but Hubble soon made discoveries that dramatically expanded the known universe. Using the 100-inch (254-cm) Hooker Telescope (then the largest telescope in the world) Hubble identified a new type of star, a Cepheid variable, that varied in luminosity with a specific period correlated with the luminosity. On January 1, 1925, Hubble announced a correlation between the distance of these objects and their period/luminosity, showing that they were located at very distant places beyond the Milky Way Galaxy. This discovery fundamentally changed the way astronomers viewed the universe.
Hubble next spent time examining the redshift of distant galaxies. Redshifts of the electromagnetic spectrum occur when the emitted or reflected light from an object is shifted toward the less energetic (red) end of the electromagnetic spectrum by the Doppler effect. This happens for objects moving away from the observer, since the radiation needs to travel a greater distance and increases its wavelength as the object moves away from the observer. Conversely, blueshifts occur when an object is moving toward the observer and the wavelengths of radiation from the object are compressed into a smaller area, causing the wavelength to decrease. Redshift was known for some time, with general knowledge that larger redshifts meant that objects were moving away faster from the observer. Hubble and his colleague Milton Humason plotted the redshifts of 46 distant objects against their distance from Earth and found a rough proportionality with increasing redshifts with distance. They found a proportionality constant to explain this correlation and stated that the farther the object or galaxy is located from Earth, the faster it is moving away—a statement that later became known as Hubble's law. The current estimate of the constant of proportionality for Hubble's Law is 70.1 +/- 1.3 km/sec/Megaparsec, although Hubble initially estimated it to be higher. The redshift means that the more distant the galaxies, the faster they are moving away from Earth and from one another. This was found to agree with Albert Einstein's equations of general relativity and supported his ideas for a homogeneous isotropic expanding universe. Interestingly, when Einstein formulated his laws of general relativity in 1917, he did not know about the redshift and Hubble's law, so he introduced a cosmological constant (a "fudge factor") into his equations to counter the result that his calculations showed the universe must be expanding. When Hubble announced his results, Einstein retracted his cos-mological constant, calling it the biggest blunder of his life, then his calculations agreed with Hubble's observations. Hubble's law is now commonly stated as "the greater the distance between any two galaxies, the greater their speed of separation." Hubble's law is one of the major observations that supports the idea that the universe was created in a big bang, and that all matter is moving away from other matter in a homogenous, isotropically expanding universe.
See also astronomy; galaxies; origin and evolution of the universe; universe.
Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. Upper Saddle River, N.J.: Addison-Wesley, 2007.
Christianson, Gale. Edwin Hubble: Mariner of the Nebulae. New York: Farrar, Straus & Giroux, 1995. Comins, Neil F. Discovering the Universe. 8th ed. New
York: W.H. Freeman, 2008. Snow, Theodore P. Essentials of the Dynamic Universe: An Introduction to Astronomy. 4th ed. St. Paul, Minn.: West, 1991.
hurricane Intense tropical storms with sustained winds of more than 74 miles per hour (119 km/hr) are known as hurricanes if they form in the northern Atlantic or eastern Pacific Oceans, cyclones if they form in the Indian Ocean near Australia, or typhoons if they form in the western North Atlantic Ocean. Most large hurricanes have a central eye with calm or light winds and clear skies or broken clouds, surrounded by an eye wall, a ring of very tall and intense thunderstorms that spin around the eye, with some of the most intense winds and rain of the entire storm system. The eye is surrounded by spiral rain bands that spin counterclockwise in the Northern Hemisphere (clockwise in the Southern Hemisphere) in toward the eye wall, moving faster and generating huge waves as they approach the center. Wind speeds increase toward the center of the storm, and the atmospheric pressure decreases to a low in the eye, uplifting the sea surface in the storm center. Surface air flows in toward the eye of the hurricane, then moves upward, often above nine miles (15 km), along the eye wall. From there it moves outward in a large outflow, until it descends outside the spiral rain bands. Air in the rain bands is ascending, whereas between the rain bands belts of descending air counter this flow. Air in the very center of the eye descends to the surface. Hurricanes drop enormous amounts of precipitation, typically spawn numerous tornadoes, and cause intense coastal damage from winds, waves, and storm surges, where the sea surface may be elevated 10 to 30 feet (3-10 m) above its normal level.
Most hurricanes form in summer and early fall over warm tropical waters when winds are light and the humidity is high. In the North Atlantic hurricane season generally runs from June through November, when the tropical surface waters are warmer than 80°F (26.5°C). They typically begin when a trigger acts on a group of unorganized thunderstorms, causing the air to begin converging and spinning. These triggers are found in the intertropical convergence zone that separates the northeast trade winds in the Northern Hemisphere from the southeast trade winds in the Southern Hemisphere. Most hurricanes form within this zone, between 5° and 20° latitude. When a low-pressure system develops in this zone during hurricane season, the isolated thunderstorms can develop into an organized convective system that strengthens to form a hurricane. Many Atlantic hurricanes form in a zone of weak convergence on the eastern side of tropical waves that form over North Africa, then move westward, where they intensify over warm tropical waters.
For hurricanes to develop, high-level winds must be mild, otherwise they might disperse the tops of the growing thunderclouds. In addition high-level winds must not be descending, since this would also inhibit the upward growth of the thunderstorms. Once the
mass of thunderstorms is organized, hurricanes gain energy by evaporating water from the warm tropical oceans. When the water vapor condenses inside the thunderclouds, this heat energy is then converted to wind energy. The upper-level clouds then move outward, causing the storm to grow stronger and decreasing the pressure in the storm's center. The low pressure in the center draws the outlying thunderstorms in toward the surface low, and these rain bands then spiral inward because of the Coriolis force. The clouds spin progressively faster as they move inward, owing to the law of conservation of angular momentum.
The Saffir-Simpson scale classifies the strength of hurricanes by measuring the damage potential of a storm, considering factors such as the central barometric pressure, maximum sustained wind speeds, and potential height of the storm surge.
• Category 1 hurricanes have central pressures greater than 980 millibars, sustained winds between 74 and 95 miles per hour (119153 km/hr), and a likely 4-5 foot (1-1.5 m) storm surge. Damage potential is minimal, with likely effects including downed power lines, ruined crops, and minor damage to weak buildings.
• Category 2 hurricanes have central barometric pressures between 979 and 965 millibars, maximum sustained winds between 96 and 110 miles per hour (155-177 km/hr), and 6-8 foot (1.8-2.4 m) storm surges. Dam age is typically moderate, including roof and chimney destruction, beached and splintered boats, destroyed crops, road signs, and traffic lights.
• Category 3 hurricanes have central barometric pressures falling between 964 and 945 millibars, sustained winds between 111 and 130 miles per hour (179-209 km/hr), and storm surges between nine and 12 feet (2.73.6 m). Category 3 hurricanes are major storms capable of extensive property damage including uprooting large trees, destroying mobile homes, and demolishing poorly constucted coastal houses. For comparison, Hurricane Katrina was a category 3 storm when it struck New Orleans in 2005.
• Category 4 storms can be devastating, with central barometric pressures falling between 940 and 920 millibars, sustained winds between 131 and 155 miles per hour (211249 km/hr), and storm surges between 13 and 18 feet (4-5.5 m). These storms typically rip the roofs off homes and businesses, destroy piers, and throw boats well inland. Waves may breach sea walls causing large-scale coastal flooding.
• Category 5 storms are massive, with central barometric pressures dropping below 920 millibars, maximum sustained winds above 155 miles per hour (249 km/hr), and storm surges of more than 18 feet (5.5 m). Storms with this power rarely hit land, but when they do they can level entire towns, moving large amounts of coastal sediments, and causing large death tolls.
Hurricanes inflict some of the most rapid and severe damage and destruction to coastal regions, and can cause numerous deaths. The number of deaths from hurricanes has been reduced dramatically in recent years owing to an increased ability to forecast the strength and landfall of hurricanes, and the ability to monitor their progress with satellites. The cost of hurricanes in terms of property damage has greatly increased, however, as more and more people build expensive homes along the coast. The greatest number of deaths from hurricanes has been from storm surges. Storm surges typically come ashore as a wall of water that rushes onto land at the forward velocity of the hurricane, as the storm waves on top of the surge are pounding the coastal area with additional energy. For instance, when Hurricane Camille hit Mississippi in 1969 with 200-mile-per-hour winds (322 km/hr), a 24-foot (7.3-m) high storm surge moved into coastal areas, killing most of the 256 who perished in this storm. Winds and tornadoes account for more deaths. Heavy rains from hurricanes also cause considerable damage. Flooding and severe erosion is often accompanied by massive mudflows and debris avalanches, such as those caused by Hurricane Mitch in Central America in 1998. In a period of several days Mitch dropped 25 to 75 inches (63.5-190.5 cm) of rain on Nicaragua and Honduras, initiating many mudslides that were the main cause of the more than 11,000 deaths from this single storm. One of the worst events was the filling and collapse of a caldera on Casitas volcano. When the caldera could hold no more water, it gave way, sending mudflows (lahars) cascading down on several villages and killing 2,000.
storm surges are water pushed ahead of storms and moving typically on to land as exceptionally high tides in front of severe ocean storms such as hurricanes. storms and storm surges can cause some of the most dramatic and rapid changes in the coastal zones and are one of the major, most unpredictable hazards to those living along coastlines. Storms that produce surges include hurricanes (which form in late summer and fall) and extratropical lows (which form in late fall through spring). Hurricanes originate in the Tropics and (for North America) migrate westward and northwestward before turning back to the northeast to return to the cold North Atlantic, weakening the storm. North Atlantic hurricanes are driven to the west by the trade winds and bend to the right because the Coriolis force makes objects moving above Earth's surface appear to curve to the right in the Northern Hemisphere. other weather conditions further modify hurricane paths, such as the location of high- and low-pressure systems and their interaction with weather fronts. Extratropical lows (also known as coastal storms, and northeasters) move eastward across North America and typically intensify when they hit the Atlantic and move up the coast. Both types of storms rotate counterclockwise, and the low pressure at storm center raises the water up to several tens of feet. This extra water moves ahead of the storms as a storm surge that is an additional height of water above the normal tidal range. The wind from the storms adds further height to the storm surge, with the total height of the surge being determined by the length, duration, and direction of wind, plus how low the pressure becomes in the center of the storm. The most destructive storm surges are those that strike low-lying communities at high tide, as the effects of the storm surge and the regular astronomical tides are cumulative. Add high winds and large waves to the storm surge and coastal storms and hurricanes are masters of disaster, as well as powerful agents of erosion. They can remove entire beaches and rows of homes, causing extensive cliff erosion and, significantly, redistributing sands in dunes and the back beach environment. Precise prediction of the height and timing of the approach of the storm surge is necessary to warn coastal residents when they need to evacuate and leave their homes.
Like many natural catastrophic events, the heights of storm surges to strike a coastline are statistically predictable. If the height of the storm surge is plotted on a semilogarithmic plot, with the height plotted in a linear interval and the frequency (in years) plotted on a logarithmic scale, then a linear slope results. This means that communities can plan for storm surges of certain height to occur once every 50, 100, 300, or 500 years, although there is no way to predict when the actual storm surges will occur. one must remember, however, that this is a long-term statistical average, and that one, two, three, or more 500-year events may occur over a relatively short period, but averaged over a long time, the events average out to once every 500 years.
Continue reading here: Extratropical cyclones
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