|
Isostatic Equilibrium
Isostasy (Greek ''ísos'' "equal", ''stásis'' "standstill") or isostatic equilibrium is the state of gravitational equilibrium between Earth's crust (or lithosphere) and mantle such that the crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Although originally defined in terms of continental crust and mantle, it has subsequently been interpreted in terms of lithosphere and asthenosphere, particularly with respect to oceanic island volcanoes, such as the Hawaiian Islands. Although Earth is a dynamic system that responds to loads in many different ways, isostasy describes the important limiting case in which crust and mantle are in static equilibrium. Certain areas (such as the Himalayas and other convergent margins) are not in isostatic equilibrium and are not well described by isostatic models. The general term 'isostasy' was coined in 1882 by the Am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arc Measurement
Arc measurement, sometimes degree measurement (german: Gradmessung), is the astrogeodetic technique of determining of the radius of Earth – more specifically, the local Earth radius of curvature of the figure of the Earth – by relating the latitude difference (sometimes also the longitude difference) and the geographic distance (arc length) surveyed between two locations on Earth's surface. The most common variant involves only astronomical latitudes and the meridian arc length and is called ''meridian arc measurement''; other variants may involve only astronomical longitude (''parallel arc measurement'') or both geographic coordinates (''oblique arc measurement''). Arc measurement campaigns in Europe were the precursors to the International Association of Geodesy (IAG). History The first known arc measurement was performed by Eratosthenes (240 BC) between Alexandria and Syene in what is now Egypt, determining the radius of the Earth with remarkable correctness. In the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Continental Glacier
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Last Glacial Maximum, the Laurentide Ice Sheet covered much of North America, the Weichselian ice sheet covered Northern Europe and the Patagonian Ice Sheet covered southern South America. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery. Although the surface is cold, the base of an ice sheet is generally warmer due to geothermal heat. In places, melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels in the ice sheet — these are ice streams. The present-day polar ice sheets are relatively young in geolo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithospheric Flexure
Lithospheric flexure (also called regional isostasy) is the process by which the lithosphere (rigid, thin outer layer of the Earth) bends under the action of forces such as the weight of a growing orogeny or changes in ice thickness related to glaciation. The lithosphere rests on the asthenosphere, a viscous layer that in geological time scales behaves like a fluid. Thus, when loaded, the lithosphere progressively reaches an isostatic equilibrium, which represents Archimedes' principle applied to geological settings. This phenomenon was first described in the late 19th century to explain the shorelines uplifted in Scandinavia by the removal of large ice massed during the last glaciation. G. K. Gilbert used it to explain the uplifted shorelines of Lake Bonneville. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Fillmore Hayford
John Fillmore Hayford (May 19, 1868 – March 10, 1925) was an eminent United States geodesist. His work involved the study of isostasy and the construction of a reference ellipsoid for approximating the figure of the Earth. The crater Hayford on the far side of the Moon is named after him. Mount Hayford, a 1,871 m mountain peak near Metlakatla, Alaska, United States, is named after him. A biography of Hayford may be found in the Biographical Memoirs of the National Academy of Sciences, 16 (5), 1935. See also *Hayford ellipsoid
The Hayford ellipsoid is a geodetic reference ellipsoid, named after the US geodesist John Fillmore Hayford (1868 ...
[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Veikko Aleksanteri Heiskanen
Veikko Aleksanteri Heiskanen (23 July 1895, in Kangaslampi – 23 October 1971, in Helsinki) was a famous Finnish geodesist. He is mostly known for his refinement of the theory of isostasy by George Airy and for his studies of the global geoid. *1931–1949 Professor of Geodesy, Helsinki University of Technology *1933–1936 Member of Finnish Parliament *1949–1961 Director, Finnish Geodetic Institute *1951–1961 Research professor, Ohio State University The Ohio State University, commonly called Ohio State or OSU, is a public land-grant research university in Columbus, Ohio. A member of the University System of Ohio, it has been ranked by major institutional rankings among the best publ ... External linksVeikko Heiskanen and Helmut Moritz(presentation) 1890s births 1971 deaths Finnish geodesists Ohio State University faculty Finnish expatriates in the United States {{Geoscience-bio-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Henry Pratt
John Henry Pratt FRS (4 June 1809 – 28 December 1871) was a British clergyman, astronomer and mathematician. A Cambridge Apostle, he joined the British East India Company in 1838 as a chaplain and later became Archdeacon of Calcutta. Although nominated as Bishop of Calcutta, the decision was rescinded at the last moment with George Cotton being appointed to the position. A gifted mathematician who worked on problems of geodesy and earth science, he was approached by the Surveyor General of India to examine the errors in surveys resulting from the attraction of the plumb-line to the mass of the Himalayan mountains. This led him to develop a theory based on a fluid earth of crustal balance which became the basis for the isostasy principle. He died in India of cholera while on a visit to Ghazipur. Biography Pratt was the second son of Josiah Pratt and Elizabeth née Jowett. His exact date of birth is debated and it is thought that he was born in London as he was baptised on 30 Ju ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
George Airy
Sir George Biddell Airy (; 27 July 18012 January 1892) was an English mathematician and astronomer, and the seventh Astronomer Royal from 1835 to 1881. His many achievements include work on planetary orbits, measuring the mean density of the Earth, a method of solution of two-dimensional problems in solid mechanics and, in his role as Astronomer Royal, establishing Greenwich as the location of the prime meridian. Biography Airy was born at Alnwick, one of a long line of Airys who traced their descent back to a family of the same name residing at Kentmere, in Westmorland, in the 14th century. The branch to which he belonged, having suffered in the English Civil War, moved to Lincolnshire and became farmers. Airy was educated first at elementary schools in Hereford, and afterwards at Colchester Royal Grammar School. An introverted child, Airy gained popularity with his schoolmates through his great skill in the construction of peashooters. From the age of 13, Airy stayed frequen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bouguer Anomaly
In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly. Definition The Bouguer anomaly g_B defined as: g_B = g_ - \delta g_B + \delta g_T Here, * g_F is the free-air gravity anomaly. * \delta g_B is the ''Bouguer correction'' which allows for the gravitational attraction of rocks between the measurement point and sea level; * \delta g_T is a ''terrain correction'' which allows for deviations of the surface from an infinite horizontal plane The free-air anomaly g_F, in its turn, is related to the observed gravity g_ as follows: g_F = g_ - g_\lambda + \delta g_F where: * g_\lambda is the correction for latitude (because the Earth is not a perfect sphere; see normal gravity); * \delta g_F is the free-air correction. Reduction A Bouguer reduction is called ''simple'' (or ''incomplete'') if the t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the north; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives; its Andaman and Nicobar Islands share a maritime border with Thailand, Myanmar, and Indonesia. Modern humans arrived on the Indian subcontinent from Africa no later than 55,000 years ago., "Y-Chromosome and Mt-DNA data support the colonization of South Asia by modern humans originating in Africa. ... Coalescence dates for most non-European populations average to between 73–55 ka.", "Modern human beings—''Homo sapiens''—originated in Africa. Then, int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andes Mountains
The Andes, Andes Mountains or Andean Mountains (; ) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18th parallel south, 18°S – 20th parallel south, 20°S latitude), and has an average height of about . The Andes extend from north to south through seven South American countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina. Along their length, the Andes are split into several ranges, separated by intermediate depression (geology), depressions. The Andes are the location of several high plateaus—some of which host major cities such as Quito, Bogotá, Cali, Arequipa, Medellín, Bucaramanga, Sucre, Mérida, Mérida, Mérida, El Alto and La Paz. The Altiplano, Altiplano plateau is the world's second-highest after the Tibetan plateau. These ranges are in turn grouped into three major di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.jpg "Click for more on -> Andes Mountains")