A crevasse is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement; the resulting intensity of the shear stress causes a breakage along the faces. Crevasses have vertical or near-vertical walls, which can melt and create seracs and other ice formations; these walls sometimes expose layers. Crevasse size depends upon the amount of liquid water present in the glacier. A crevasse may be as deep as 100 metres, as wide as 20 metres, up to several hundred metres long. A crevasse may be covered, but not filled, by a snow bridge made of the previous years' accumulation and snow drifts; the result is that crevasses are rendered invisible, thus lethal to anyone attempting to navigate their way across a glacier. A snow bridge over an old crevasse may begin to sag, providing some landscape relief, but this cannot be relied upon.
Anyone planning to travel on a glacier should be trained in crevasse rescue. The presence of water in a crevasse can increase its penetration. Water-filled crevasses may reach the bottom of glaciers or ice sheets and provide a direct hydrologic connection between the surface, where significant summer melting occurs, the bed of the glacier, where additional water may moisten and lubricate the bed and accelerate ice flow. Longitudinal crevasses form parallel to flow, they develop such as where a valley widens or bends. They are concave down and form an angle greater than 45° with the margin. Splashing crevasses result from shear stress from the margin of the glacier and longitudinal compressing stress from lateral extension, they extend from the glacier's margin and are concave up with respect to glacier flow, making an angle less than 45° with the margin. At the centre line of the glacier, there is zero pure shear from the margins, so this area is crevasse-free. Transverse crevasses are the most common crevasse type.
They form in a zone of longitudinal extension where the principal stresses are parallel to the direction of glacier flow, creating extensional tensile stress. These crevasses stretch across the glacier transverse to cross-glacier, they form where a valley becomes steeper. Bergschrund – A crevasse between moving glacier ice and the stagnant ice or firn above Bowie Crevasse Field Glaciology – Scientific study of ice and natural phenomena involving ice Boon, S. & M. J. Sharp. "The role of hydrologically-driven ice fracture in drainage system evolution on an Arctic glacier". Geophysical Research Letters. 30: 1916. CS1 maint: Uses authors parameter Colgan, W. & Rajaram, H. & Abdalati, W. & McCutchan, C. & Mottram, R. & Moussavi, M. S. & Grigsby, S.. "Glacier crevasses: Observations and mass balance implications". Rev. Geophys. 54. Doi:10.1002/2015RG000504. CS1 maint: Uses authors parameter "Crevasse". Encyclopædia Britannica. Das, S. B. Joughin, I. & Behn, M. D. & Howat, I. M. & King, M. A. & Lizarralde, D. & Bhatia, M.
P.. "Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage". Science. 320: 778. CS1 maint: Uses authors parameter Mountaineering: The Freedom of the Hills. ISBN 0-89886-309-0. Paterson, W. S. B.. The Physics of Glaciers. ISBN 0-7506-4742-6. CS1 maint: Uses authors parameter van der Veen, C. J.. "Fracture mechanics approach to penetration of surface crevasses on glaciers". Cold Regions Technology. 27: 31–47. CS1 maint: Uses authors parameter Zwally, H. J. & Abdalati, W. & Herring, T. & Larson, K. & Saba, J. & Steffen, K.. "Greenland ice-sheet". Science. 297: 218–222. CS1 maint: Uses authors parameter Media related to Crevasses at Wikimedia Commons
Mount Church (Alaska)
Mount Church is a 7,621-foot mountain in the Alaska Range, in Denali National Park and Preserve, overlooking Ruth Glacier. Mountain peaks of Alaska
Granite is a common type of felsic intrusive igneous rock, granular and phaneritic in texture. Granites can be predominantly white, pink, or gray depending on their mineralogy; the word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Speaking, granite is an igneous rock with between 20% and 60% quartz by volume, at least 35% of the total feldspar consisting of alkali feldspar, although the term "granite" is used to refer to a wider range of coarse-grained igneous rocks containing quartz and feldspar; the term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks consist of feldspar, quartz and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole peppering the lighter color minerals; some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic.
A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids; the extrusive igneous rock equivalent of granite is rhyolite. Granite is nearly always massive and tough; these properties have made granite a widespread construction stone throughout human history. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength lies above 200 MPa, its viscosity near STP is 3–6·1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. Granite is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz, alkali feldspar and plagioclase feldspar on the A-Q-P half of the diagram.
True granite contains both alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite; when a granitoid contains less than 10% orthoclase, it is called tonalite. A granite containing both muscovite and biotite micas is called two-mica granite. Two-mica granites are high in potassium and low in plagioclase, are S-type granites or A-type granites. A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: Granite containing rock is distributed throughout the continental crust. Much of it was intruded during the Precambrian age. Outcrops of granite tend to form rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite occurs as small, less than 100 km2 stock masses and in batholiths that are associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are associated with the margins of granitic intrusions.
In some locations coarse-grained pegmatite masses occur with granite. Granite is more common in continental crust than in oceanic crust, they are crystallized from felsic melts which are less dense than mafic rocks and thus tend to ascend toward the surface. In contrast, mafic rocks, either basalts or gabbros, once metamorphosed at eclogite facies, tend to sink into the mantle beneath the Moho. Granitoids have crystallized from felsic magmas that have compositions near a eutectic point. Magmas are composed of minerals in variable abundances. Traditionally, magmatic minerals are crystallized from the melts that have separated from their parental rocks and thus are evolved because of igneous differentiation. If a granite has a cooling process, it has the potential to form larger crystals. There are peritectic and residual minerals in granitic magmas. Peritectic minerals are generated through peritectic reactions, whereas residual minerals are inherited from parental rocks. In either case, magmas will evolve to the eutectic for crystallization upon cooling.
Anatectic melts are produced by peritectic reactions, but they are much less evolved than magmatic melts because they have not separated from their parental rocks. The composition of anatectic melts may change toward the magmatic melts through high-degree fractional crystallization. Fractional crystallisation serves to reduce a melt in iron, titanium and sodium, enrich the melt in potassium and silicon – alkali feldspar and quartz, are two of the defining constituents of granite; this process operates regardless of the origin of parental magmas to granites, regardless of their chemistry. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was; the final texture and composition of a granite are distinctive as to its parental rock. For instance, a granite, derived from partial melting of meta
Matanuska-Susitna Borough, Alaska
Matanuska-Susitna Borough is a borough located in the U. S. state of Alaska. The borough is part of the Anchorage Metropolitan Statistical Area, along with the municipality of Anchorage on its south; the Mat-Su Borough is so designated because it contains the entire Susitna rivers. These rivers empty into Cook Inlet, the southern border of the Mat-Su Borough; this area is one of the few agricultural areas of Alaska. The borough seat is Palmer, the largest city is Wasilla; as of the 2010 census, the population was 88,995. According to the U. S. Census Bureau, the borough has a total area of 25,258 square miles, of which 24,608 square miles is land and 650 square miles is water. Denali Borough, Alaska - north Southeast Fairbanks Census Area, Alaska - northeast Valdez-Cordova Census Area, Alaska - east Municipality of Anchorage, Alaska - south Kenai Peninsula Borough, Alaska - south Bethel Census Area, Alaska - west Yukon-Koyukuk Census Area, Alaska - west Chugach National Forest Denali National Park and Preserve Denali Wilderness Lake Clark National Park and Preserve Lake Clark Wilderness As of the census of 2000, there were 59,322 people, 20,556 households, 15,046 families residing in the borough.
The population density was 2 people per square mile. There were 27,329 housing units at an average density of 1 per square mile; the racial makeup of the borough was 87.55% White, 0.69% Black or African American, 5.50% Native American, 0.70% Asian, 0.12% Pacific Islander, 0.86% from other races, 4.57% from two or more races. 2.50% of the population were Hispanic or Latino of any race. There were 20,556 households out of which 42.30% had children under the age of 18 living with them, 58.90% were married couples living together, 9.10% had a female householder with no husband present, 26.80% were non-families. 20.30% of all households were made up of individuals and 4.10% had someone living alone, 65 years of age or older. The average household size was 2.84 and the average family size was 3.29. In the borough the population was spread out with 32.20% under the age of 18, 7.40% from 18 to 24, 31.10% from 25 to 44, 23.40% from 45 to 64, 5.90% who were 65 years of age or older. The median age was 34 years.
For every 100 females, there were 108.20 males. For every 100 females age 18 and over, there were 108.10 males. Schools in the borough are administered by the Matanuska-Susitna Borough School District. Matanuska-Susitna Borough was the largest of fifteen county-equivalents in America carried by Ross Perot in the 1992 presidential election. Vern Halter is the mayor of the Matanuska-Susitna Borough; the borough has a strong manager form of government. John Moosey is the borough manager. Long-time Manager John Duffy retired in 2010. Houston Palmer Wasilla Alexander Creek Dinglishna Hills In July 2018, the borough's computer systems, including the library and animal shelter, were hit by a ransomware attack, forcing employees to do without computers, using electric typewriters where available; the borough incurred over $2 million in costs. The method is thought to have been a targeted phishing e-mail. Matanuska-Susitna Valley List of Airports in the Matanuska-Susitna Borough Matanuska Formation official government website Borough Facebook Borough newsroom Borough map, 2000 census: Alaska Department of Labor Borough map, 2010 census: Alaska Department of Labor
Climbing is the activity of using one's hands, feet, or any other part of the body to ascend a steep object. It is done for locomotion and competition, in trades that rely on it, in emergency rescue and military operations, it is done indoors and out, on man-made structures. Guides, such as professional mountain guides, have been an essential element of pursuing the sport in the natural environment, remain so today. Climbing activities include: Bouldering: Ascending boulders or small outcrops with climbing shoes and a chalk bag or bucket. Instead of using a safety rope from above, injury is avoided using a crash pad and a human spotter Buildering: Ascending the exterior skeletons of buildings without protective equipment. Canyoneering: Climbing along canyons for sport or recreation. Chalk climbing: Ascending chalk cliffs uses some of the same techniques as ice climbing. Competition climbing: A formal, competitive sport of recent origins practiced on artificial walls that resemble natural formations.
The International Federation of Sport Climbing is the official organization governing competition rock climbing worldwide and is recognized by the IOC and GAISF and is a member of the International World Games Association. The UIAA is the official organization governing competition ice climbing worldwide. Competition climbing has three major disciplines: Lead and Speed. Free Climbing: a form of rock climbing in which the climber uses climbing equipment such as ropes and other means of climbing protection, but only to protect against injury during falls and not to assist progress. Ice climbing: Ascending ice or hard snow formations using special equipment ice axes and crampons. Techniques of protecting the climber are similar to those of rock climbing, with protective devices adapted to frozen conditions. Indoor climbing: Top roping, lead climbing, bouldering artificial walls with bolted holds in a climbing gym. Ladder climbing: Climbing ladders for exercise; this may involve climbing up and down the underside of a ladder, or along a horizontally aligned ladder or'monkey bars'.
The ladder may be climbed going backwards, or sideways. Lumberjack tree-trimming and competitive tree-trunk or pole climbing for speed using spikes and belts. Mallakhamba: A traditional Indian sport which combines climbing a pole or rope with the performance of aerial Yoga and gymnastics. Mountaineering: Ascending mountains for sport or recreation, it involves rock and/or ice climbing. Pole climbing: Climbing poles and masts without equipment. Rock climbing: Ascending rock formations using climbing shoes and a chalk bag. Equipment such as ropes, nuts and camming devices are employed, either as a safeguard or for artificial aid. Rope access: Industrial climbing abseiling, as an alternative to scaffolding for short works on exposed structures. Rope climbing: Climbing a short, thick rope for speed. Not to be confused with roped climbing, as in rock or ice climbing. Scrambling which includes easy rock climbing, is considered part of hillwalking. Sport climbing is a form of rock climbing that relies on permanent anchors fixed to the rock, bolts, for protection.
Top roping: Ascending a rock climbing route protected by a rope anchored at the top and protected by a belayer below Traditional climbing is a form of climbing without fixed anchors and bolts. Climbers place removable protection such as camming devices and other passive and active protection that holds the rope to the rock in the event of a fall and/or when weighted by a climber. Solo climbing: Solo climbing or soloing is a style of climbing in which the climber climbs alone, without somebody belaying them; when free soloing, an error is fatal as no belay systems are being used. Soloing can be self-belayed, hence minimizing the risks. Tree climbing: Recreationally ascending trees using ropes and other protective equipment. A tower climber is a professional who climbs broadcasting or telecommunication towers or masts for maintenance or repair. Rock and tree climbing all utilize ropes for safety or aid. Pole climbing and rope climbing were among the first exercises to be included in the origins of modern gymnastics in the late 18th century and early 19th century.
Aid climbing Clean climbing Climbing clubs Climbing wall Climbing equipment Climbing organisations Fall factor List of climbers – notable rock and ice climbers List of climbing topics Glossary of climbing terms Glossary of knots common in climbing Outdoor education Outdoor activity Rock climbing Running belay Parkour Scrambling Solo climbing Speed climbing Climbing at Curlie
Alaska is a U. S. state in the northwest extremity of North America, just across the Bering Strait from Asia. The Canadian province of British Columbia and territory of Yukon border the state to the east and southeast, its most extreme western part is Attu Island, it has a maritime border with Russia to the west across the Bering Strait. To the north are the Chukchi and Beaufort seas—southern parts of the Arctic Ocean; the Pacific Ocean lies to southwest. It is the largest U. S. state by the seventh largest subnational division in the world. In addition, it is the most sparsely populated of the 50 United States. Half of Alaska's residents live within the Anchorage metropolitan area. Alaska's economy is dominated by the fishing, natural gas, oil industries, resources which it has in abundance. Military bases and tourism are a significant part of the economy; the United States purchased Alaska from the Russian Empire on March 30, 1867, for 7.2 million U. S. dollars at two cents per acre. The area went through several administrative changes before becoming organized as a territory on May 11, 1912.
It was admitted as the 49th state of the U. S. on January 3, 1959. The name "Alaska" was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula, it was derived from an Aleut-language idiom. It means object to which the action of the sea is directed. Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U. S. state on continental North America. It is technically part of the continental U. S. but is sometimes not included in colloquial use. S. called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system; the state is bordered by Yukon and British Columbia in Canada, to the east, the Gulf of Alaska and the Pacific Ocean to the south and southwest, the Bering Sea, Bering Strait, Chukchi Sea to the west and the Arctic Ocean to the north.
Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only 3 miles apart. Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, the next largest state. Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the combined area of the next three largest states: Texas and Montana, it is larger than the combined area of the 22 smallest U. S. states. There are no defined borders demarcating the various regions of Alaska, but there are six accepted regions: The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula. Rural unpopulated areas south of the Alaska Range and west of the Wrangell Mountains fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez.
Referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase; the region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, Ketchikan, at one time Alaska's largest city; the Alaska Marine Highway provides a vital surface transportation link throughout the area, as only three communities enjoy direct connections to the contiguous North American road system. Designated in 1963; the Interior is the largest region of Alaska. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali is the highest mountain in North America. Southwest Alaska is a sparsely inhabited region stretching some 500 miles inland from the Bering Sea. Most of the population lives along the coast.
Kodiak Island is located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands; the North Slope is tundra peppered with small villages. The area is known for its massive reserves of crude oil, contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field; the city of Utqiagvik known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and containing the Kobuk River valley, is regarded as being part of this region. However, the respective Inupiat of the No
Denali is the highest mountain peak in North America, with a summit elevation of 20,310 feet above sea level. With a topographic prominence of 20,156 feet and a topographic isolation of 4,629 miles, Denali is the third most prominent and third most isolated peak on Earth, after Mount Everest and Aconcagua. Located in the Alaska Range in the interior of the U. S. state of Alaska, Denali is the centerpiece of Preserve. The Koyukon people who inhabit the area around the mountain have referred to the peak as "Denali" for centuries. In 1896, a gold prospector named it "Mount McKinley" in support of then-presidential candidate William McKinley. In August 2015, following the 1975 lead of the State of Alaska, the United States Department of the Interior announced the change of the official name of the mountain to Denali. In 1903, James Wickersham recorded the first attempt at climbing Denali, unsuccessful. In 1906, Frederick Cook claimed the first ascent, proven to be false; the first verifiable ascent to Denali's summit was achieved on June 7, 1913, by climbers Hudson Stuck, Harry Karstens, Walter Harper, Robert Tatum, who went by the South Summit.
In 1951, Bradford Washburn pioneered the West Buttress route, considered to be the safest and easiest route, therefore the most popular in use. On September 2, 2015, the U. S. Geological Survey announced that the mountain is 20,310 feet high, not 20,320 feet, as measured in 1952 using photogrammetry. Denali is a granitic pluton lifted by tectonic pressure from the subduction of the Pacific Plate beneath the North American Plate; the forces that lifted Denali cause many deep earthquakes in Alaska and the Aleutian Islands. The Pacific Plate is seismically active beneath Denali, a tectonic region, known as the "McKinley cluster". Denali has a summit elevation of 20,310 feet above sea level, making it the highest peak in North America and the northernmost mountain above 6,000 meters elevation in the world. Measured from base to peak at some 18,000 ft, it is among the largest mountains situated above sea level. Denali rises from a sloping plain with elevations from 1,000 to 3,000 ft, for a base-to-peak height of 17,000 to 19,000 ft.
By comparison, Mount Everest rises from the Tibetan Plateau at a much higher base elevation. Base elevations for Everest range from 13,800 ft on the south side to 17,100 ft on the Tibetan Plateau, for a base-to-peak height in the range of 12,000 to 15,300 ft. Denali's base-to-peak height is little more than half the 33,500 ft of the volcano Mauna Kea, which lies under water. Denali has two significant summits: the South Summit is the higher one, while the North Summit has an elevation of 19,470 ft and a prominence of 1,270 ft; the North Summit is sometimes counted as sometimes not. Five large glaciers flow off the slopes of the mountain; the Peters Glacier lies on the northwest side of the massif, while the Muldrow Glacier falls from its northeast slopes. Just to the east of the Muldrow, abutting the eastern side of the massif, is the Traleika Glacier; the Ruth Glacier lies to the southeast of the mountain, the Kahiltna Glacier leads up to the southwest side of the mountain. With a length of 44 mi, the Kahiltna Glacier is the longest glacier in the Alaska Range.
The Koyukon Athabaskans who inhabit the area around the mountain have for centuries referred to the peak as Dinale or Denali. The name is based on a Koyukon word for "high" or "tall". During the Russian ownership of Alaska, the common name for the mountain was Bolshaya Gora, the Russian translation of Denali, it was called Densmore's Mountain in the late 1880s and early 1890s after Frank Densmore, an Alaskan prospector, the first European to reach the base of the mountain. In 1896, a gold prospector named it McKinley as political support for then-presidential candidate William McKinley, who became president the following year; the United States formally recognized the name Mount McKinley after President Wilson signed the Mount McKinley National Park Act of February 26, 1917. In 1965, Lyndon B. Johnson declared the north and south peaks of the mountain the "Churchill Peaks", in honor of British statesman Winston Churchill; the Alaska Board of Geographic Names changed the name of the mountain to Denali in 1975, how it is called locally.
However, a request in 1975 from the Alaska state legislature to the United States Board on Geographic Names to do the same at the federal level was blocked by Ohio congressman Ralph Regula, whose district included McKinley's hometown of Canton. On August 30, 2015, just ahead of a presidential visit to Alaska, the Barack Obama administration announced the name Denali would be restored in line with the Alaska Geographic Board's designation. U. S. Secretary of the Interior Sally Jewell issued the order changing the name to Denali on August 28, 2015, effective immediately. Jewell said the change had been "a long time coming"; the renaming of the mountain received praise from Alaska's senior U. S. senator, Lisa Murkowski, who had introduced legislation to accomplish the name change, but it drew criticism from several politicians from Pres