A river delta is a landform that forms from deposition of sediment, carried by a river as the flow leaves its mouth and enters slower-moving or stagnant water. This occurs where a river enters an ocean, estuary, reservoir, or another river that cannot carry away the supplied sediment; the size and shape of a delta is controlled by the balance between watershed processes that supply sediment, receiving basin processes that redistribute and export that sediment. The size and location of the receiving basin plays an important role in delta evolution. River deltas are important in human civilization, as they are major agricultural production centers and population centers, they can impact drinking water supply. They are ecologically important, with different species' assemblages depending on their landscape position. River deltas form when a river carrying sediment reaches either a body of water, such as a lake, ocean, or reservoir, another river that cannot remove the sediment enough to stop delta formation, or an inland region where the water spreads out and deposits sediments.
The tidal currents cannot be too strong, as sediment would wash out into the water body faster than the river deposits it. The river must carry enough sediment to layer into deltas over time; the river's velocity decreases causing it to deposit the majority, if not all, of its load. This alluvium builds up to form the river delta; when the flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity, which diminishes the ability of the flow to transport sediment; as a result, sediment drops out of deposits. Over time, this single channel builds a deltaic lobe; as the deltaic lobe advances, the gradient of the river channel becomes lower because the river channel is longer but has the same change in elevation. As the slope of the river channel decreases, it becomes unstable for two reasons. First, gravity makes the water flow in the most direct course down slope. If the river breaches its natural levees, it spills out into a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope.
Second, as its slope gets lower, the amount of shear stress on the bed decreases, which results in deposition of sediment within the channel and a rise in the channel bed relative to the floodplain. This makes it easier for the river to breach its levees and cut a new channel that enters the body of standing water at a steeper slope; when the channel does this, some of its flow remains in the abandoned channel. When these channel-switching events occur, a mature delta develops a distributary network. Another way these distributary networks form is from deposition of mouth bars; when this mid-channel bar is deposited at the mouth of a river, the flow is routed around it. This results in additional deposition on the upstream end of the mouth-bar, which splits the river into two distributary channels. A good example of the result of this process is the Wax Lake Delta. In both of these cases, depositional processes force redistribution of deposition from areas of high deposition to areas of low deposition.
This results in the smoothing of the planform shape of the delta as the channels move across its surface and deposit sediment. Because the sediment is laid down in this fashion, the shape of these deltas approximates a fan; the more the flow changes course, the shape develops as closer to an ideal fan, because more rapid changes in channel position results in more uniform deposition of sediment on the delta front. The Mississippi and Ural River deltas, with their bird's-feet, are examples of rivers that do not avulse enough to form a symmetrical fan shape. Alluvial fan deltas, as seen by their name and more approximate an ideal fan shape. Most large river deltas discharge to intra-cratonic basins on the trailing edges of passive margins due to the majority of large rivers such as the Mississippi, Amazon, Ganges and Yangtze discharging along passive continental margins; this phenomenon is due to three big factors: topography, basin area, basin elevation. Topography along passive margins tend to be more gradual and widespread over a greater area enabling sediment to pile up and accumulate overtime to form large river deltas.
Topography along active margins tend to be steeper and less widespread, which results in sediments not having the ability to pile up and accumulate due to the sediment traveling into a steep subduction trench rather than a shallow continental shelf. There are many other smaller factors that could explain why the majority of river deltas form along passive margins rather than active margins. Along active margins, orogenic sequences cause tectonic activity to form over-steepened slopes, brecciated rocks, volcanic activity resulting in delta formation to exist closer to the sediment source; when sediment does not travel far from the source, sediments that build up are coarser grained and more loosely consolidated, therefore making delta formation more difficult. Tectonic activity on active margins causes the formation of river deltas to form closer to the sediment source which may affect channel avulsion, delta lobe switching, auto cyclicity. Active margin river deltas tend to be much smaller and less abundant but may transport similar amounts of sediment.
However, the sediment is never piled up in thick sequences due to the sediment traveling and depositing in de
A spruce is a tree of the genus Picea, a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal regions of the Earth. Spruces are large trees, from about 20–60 m tall when mature, have whorled branches and conical form, they can be distinguished from other members of the pine family by their needles, which are four-sided and attached singly to small persistent peg-like structures on the branches, by their cones, which hang downwards after they are pollinated. The needles are shed. In other similar genera, the branches are smooth. Spruce are used as food plants by the larvae of some Lepidoptera species, such as the eastern spruce budworm, they are used by the larvae of gall adelgids. In the mountains of western Sweden, scientists have found a Norway spruce, nicknamed Old Tjikko, which by reproducing through layering, has reached an age of 9,550 years and is claimed to be the world's oldest known living tree; the word spruce comes from a Middle English adjective spruse which meant from Prussia.
The adjective comes from an unknown alteration of an Old French form of Prussia - Pruce, which itself comes from New Latin, which adapted it from Old Prussian. Spruce and Sprws seem to have been generic terms for commodities brought to England by Hanseatic merchants, the tree thus was believed to be particular to Prussia, which for a time was figurative in England as a land of luxuries. DNA analyses have shown that traditional classifications based on the morphology of needle and cone are artificial. A recent study found that P. breweriana had a basal position, followed by P. sitchensis, the other species were further divided into three clades, suggesting that Picea originated in North America. Spruce has been found in the fossil record from the early Cretaceous, 136 million years ago. Thirty-five named species of spruce exist in the world; the Plant List has 59 accepted spruce names. Basal species: Picea breweriana – Brewer's spruce, Klamath Mountains, North America. Beyond that, determination can become more difficult.
Intensive sampling in the Smithers/Hazelton/Houston area of British Columbia showed Douglas, according to Coates et al. that cone scale morphology was the feature most useful in differentiating species of spruce. Daubenmire, after range-wide sampling, had recognized the importance of the 2 latter characters. Taylor had noted that the most obvious morphological difference
The Alaska Range is a narrow, 650-km-long mountain range in the southcentral region of the U. S. state of Alaska, from Lake Clark at its southwest end to the White River in Canada's Yukon Territory in the southeast. The highest mountain in North America, Denali, is in the Alaska Range, it is part of the American Cordillera. The range is the highest in the world outside Asia and the Andes; the range forms a east-west arc with its northernmost part in the center, from there trending southwest towards the Alaska Peninsula and the Aleutians, trending southeast into the Pacific Coast Ranges. The mountains act as a high barrier to the flow of moist air from the Gulf of Alaska northwards, thus has some of the harshest weather in the world; the heavy snowfall contributes to a number of large glaciers, including the Canwell, Black Rapids, Yanert, Eldridge, Ruth and Kahiltna Glaciers. Four major rivers cross the Range, including the Delta River, Nenana River in the center of the range and the Nabesna and Chisana Rivers to the east.
The range is part of the Pacific Ring of Fire, the Denali Fault that runs along the southern edge of the range is responsible for a number of earthquakes. Mount Spurr is a stratovolcano located in the northeastern end of the Aleutian Volcanic Arc of Alaska, USA which has two vents, the summit and nearby Crater Peak. Parts of the range are protected within Wrangell-St. Elias National Park and Preserve, Denali National Park and Preserve, Lake Clark National Park and Preserve; the George Parks Highway from Anchorage to Fairbanks, the Richardson Highway from Valdez to Fairbanks, the Tok Cut-Off from Gulkana Junction to Tok, Alaska pass through low parts of the range. The Alaska Pipeline parallels the Richardson Highway; the name "Alaskan Range" appears to have been first applied to these mountains in 1869 by naturalist W. H. Dall; the name became "Alaska Range" through local use. In 1849 Constantin Grewingk applied the name "Tschigmit" to this mountain range. A map made by the General Land Office in 1869 calls the southwestern part of the Alaska Range the "Chigmit Mountains" and the northeastern part the "Beaver Mountains".
However the Chigmit Mountains are now considered part of the Aleutian Range. Denali Mount Foraker Mount Hunter Mount Hayes Mount Silverthrone Mount Moffit Mount Deborah Mount Huntington Mount Brooks Mount Russell Neacola Mountains Revelation Mountains Teocalli Mountains Kichatna Mountains Central Alaska Range/Denali Massif Eastern Alaska Range/Hayes Range Delta Mountains Mentasta Mountains Nutzotin Mountains Mentasta Lake to Kitchatna Mountains: Scott Woolums, George Beilstein, Steve Eck, Larry Coxen by skis: first traverse. 375 miles in 45 days. Canada to Lake Clark: Roman Dial, Carl Tobin, Paul Adkins by mountain bike and packraft: first full length traverse. 775 miles in 42 days. Tok to Lake Clark: Kevin Armstrong, Doug Woody, Jeff Ottmers by snowshoe and packraft: first foot traverse. 620 miles in 90 days. Lake Clark to Mentasta Lake: Gavin McClurg by paraglider and foot: first vol-biv traverse. 466 miles in 37 days. Summit Lake, Alaska Churkin, M. Jr. and C. Carter.. Stratigraphy and graptolites of an Ordovician and Silurian sequence in the Terra Cotta Mountains, Alaska Range, Alaska.
Washington, D. C.: U. S. Department of the Interior, U. S. Geological Survey
An ice road is a winter road, or part thereof, that runs on a frozen water surface in cold regions. Ice roads allow temporary transport to isolated areas with no permanent road access, they reduce transportation cost of materials that otherwise would ship as expensive air freight, they allow movement of large or heavy objects for which air freight is impractical. Ice roads may be winter substitutes for summer ferry services. Ferry service and an ice crossing may operate yearly at the same time for several weeks. Ice roads provide a flat, smooth driving surface devoid of trees and other obstacles, they can be snow plowed, may comprise a series of short overland portages - overland segments linking lakes. Similar to ice roads, ice runways are common in the polar regions and include the blue ice runways such as Wilkins Runway in Antarctica or lake ice runways like Doris Lake Aerodrome in the Arctic. Ice can be used as an emergency landing surface. In general, these roads are built in areas where construction of year-round roads is expensive due to boggy muskeg land and a number of other reasons.
In the winter, these obstacles are therefore easier to cross. Ice roads, such as the stretch between Inuvik and Tuktoyaktuk, Northwest Territories, provide an level driving surface with few detours several months of the year; when frozen in winter, the waterway crossings can be built up with auger holes to flood and thicken the crossing. The act of clearing snow makes ice thicker by exposing the road directly to subfreezing air. In the summer, after the ice melts, effects of the roads can still be seen from overhead in a bush plane, as bare strips remain on the lake floor where the ice blocked light and prevented plants and algae from growing. There is a car ferry used in summer time. There are periods in spring and fall where there is too much ice for the ferry, but too little for an ice road. While easier to drive across in the winter than land, roads over water present a great danger to anyone using them. Speeds are limited to 25 km/h to prevent a truck's weight from causing waves under the surface.
These waves can dislodge the ice from the shoreline and create a hazard. Another hazard on large lakes is the pressure ridge, a break in the ice created by the expansion and contraction of the surface ice due to variations in temperature; the roads are the domain of large trucks, although lighter vehicles, such as pickup trucks small cars, can be seen, as are snowmobiles. Use of ice as the main construction material allows unusual construction techniques: to make a ramp to get the road over a step such as the shore of a lake, for example, lake water is pumped out and mixed with snow to make slush, formed into the shape of the ramp, allowed to freeze in the intense cold. Worn and damaged roads are repaired by flooding with shallow water that freezes into a new surface layer; the South Pole Traverse is 1,400 km long and links the United States' McMurdo Station on the coast to the Amundsen–Scott South Pole Station. It is not paved. There are flags to mark the route; the United States Antarctic Program maintains two ice roads during the austral summer.
One provides access to Pegasus Field on the Ross Ice Shelf. The ice road between Pegasus Field and McMurdo Station is about 14 miles; the other road provides access to the Ice Runway, on sea ice. The road between the Ice Runway and McMurdo Station varies in length from year to year depending on many factors, including ice stability; these roads are critical for resupplying McMurdo Station, Scott Base, Amundsen–Scott South Pole Station. Some of the first ice roads in history were built in the 1930s in northern Canada, for use by caterpillar sleds pulling heavy loads called tractor trains for mines where loads were too heavy for transport by aircraft and the soil too boggy for standard roads when the land was not frozen. Tractor-freighting was phased out in the north and replaced with truck transport over well-maintained ice roads. Winter roads and ice roads in Canada are found in northern parts of some provinces, as well as the sparsely-populated northern territories of Yukon, Northwest Territories and Nunavut.
In Nunavut, while there are a number of permanent roads within the territory, the Tibbitt to Contwoyto Winter Road, linking Nunavut to Tibbitt Lake in the Northwest Territories, forms the territory's only road access to the rest of North America's road network. Winter roads in the Northwest Territories, most notably the Tuktoyaktuk Winter Road, link various isolated communities and mineral exploration sites to the territory's highway network. Winter roads may be found in the sparsely populated northernmost regions of some Canadian provinces. Most communities north of Ontario's Albany River are served by winter roads. Most of these roads in Northwestern Ontario are linked to the Northern Ontario Resource Trail, a permanent gravel road which extends northerly from the end of Highway 599 at Pickle Lake, the northernmost community in the province with year-round highway access. In Northeastern Ontario, some communities are linked to Moosonee, a town that has rail access but no road access to the south.
Saskatchewan has an ice road in the southern part of the province at the Riverhurst Ferry. Transport links between Russia and
Yukon–Koyukuk Census Area, Alaska
Yukon–Koyukuk Census Area is a census area in the U. S. state of Alaska. As of the 2010 census, the population was 5,588, it has the largest area of any county-equivalent in the United States. It therefore has no borough seat, its largest communities are the cities of Galena, in the west, Fort Yukon, in the northeast. According to the U. S. Census Bureau, the census area has 147,805 square miles, of which 145,505 square miles is land and 2,300 square miles is water; the area is the same size as the U. S. state of Montana or the country of Germany. The area is bigger than 47 of the 50 states, with only California and Alaska itself being bigger than the county size, its population density, at 0.0449 inhabitants per square mile, is the lowest in the United States. As of the census of 2000, there were 6,551 people, 2,309 households, 1,480 families residing in the census area; the population density was 22.3 square miles per person. It is the least densely populated county-equivalent of all 3,141 county-equivalents of the United States.
There were 3,917 housing units at an average density of 0.027 per square mile. The racial makeup of the census area was 24.27% White, 0.09% Black or African American, 70.89% Native American, 0.37% Asian, 0.05% Pacific Islander, 0.43% from other races, 3.91% from two or more races. 1.19% of the population were Hispanic or Latino of any race. 12.95% reported speaking an Athabaskan language at home. There were 2,309 households out of which 38.90% had children under the age of 18 living with them, 36.90% were married couples living together, 16.90% had a female householder with no husband present, 35.90% were non-families. 30.50% of all households were made up of individuals and 6.20% had someone living alone, 65 years of age or older. The average household size was 2.81 and the average family size was 3.53. In the census area the population was spread out with 35.00% under the age of 18, 8.70% from 18 to 24, 26.90% from 25 to 44, 22.10% from 45 to 64, 7.30% who were 65 years of age or older. The median age was 31 years.
For every 100 females there were 118.60 males. For every 100 females age 18 and over, there were 122.60 males. Galena City School District operates public schools serving Galena. Nenana City School District operates public schools serving Nenana. Yukon–Koyukuk School District and Yukon Flats School District operate public schools serving rural areas. List of airports in Yukon–Koyukuk Census Area Crow Lake U. S. Geological Survey Geographic Names Information System: Yukon–Koyukuk Census Area "Census Area map: Alaska Department of Labor"
The Yukon–Kuskokwim Delta is a river delta located where the Yukon and Kuskokwim rivers empty into the Bering Sea on the west coast of the U. S. state of Alaska. At 129,500 square kilometers in size, it is one of the largest deltas in the world, it is larger than the Mississippi River Delta, comparable in size to the entire U. S. state of Louisiana. The delta, which consists of tundra, is protected as part of the Yukon Delta National Wildlife Refuge; the delta has 25,000 residents. 85 % of these are Alaska Natives: Athabaskan Indians. The main population center and service hub is the city of Bethel, with an estimated population of around 6,219. Bethel is surrounded by 49 smaller villages, with the largest villages consisting of over 1,000 people. Most residents live a traditional subsistence lifestyle of hunting and gathering. More than 30 percent have cash incomes well below the federal poverty threshold; the area has no roads. Bethel is the location of the Yukon Kuskokwim Correctional Center. Yukon Delta National Wildlife Refuge In rural Alaska villages, families struggle to survive – CNN
Alaska Natives are indigenous peoples of Alaska, United States and include: Iñupiat, Aleut, Tlingit, Tsimshian, a number of Northern Athabaskan cultures. They are defined by their language groups. Many Alaska Natives are enrolled in federally recognized Alaska Native tribal entities, who in turn belong to 13 Alaska Native Regional Corporations, who administer land and financial claims. Ancestors of Alaska Natives migrated into the area thousands of years ago, in at least two different waves; some are descendants of a third wave of migration in which people settled across the northern part of North America. They never migrated to southern areas. For this reason, genetic studies show they are not related to Native Americans in South America. Throughout the Arctic and the circumpolar north, the ancestors of Alaska Natives established varying indigenous, complex cultures that have succeeded each other over time, they developed sophisticated ways to deal with the challenging climate and environment, cultures rooted in the place.
Historic groups have been defined by their languages, which belong to several major language families. Today, Alaska Natives comprise over 15% of the population of Alaska. Below is a full list of the different Alaska Native peoples, which are defined by their historic languages. Within each culture are many different tribes. Ancient Beringian Alaskan Athabaskans Ahtna Deg Hit'an Dena'ina Gwich'in Hän Holikachuk Koyukon Lower Tanana Tanacross Upper Tanana Upper Kuskokwim Eyak Tlingit Haida Tsimshian Eskimo Iñupiat, an Inuit group Yupik Siberian Yupik Yup'ik Cup'ik Nunivak Cup'ig Sugpiaq ~ Alutiiq Chugach Sugpiaq Koniag Alutiiq Aleut The Alaska Natives Commission estimated that there were about 86,000 Alaska Natives living in Alaska in 1990, with another 17,000 who lived outside Alaska. A 2013 study by the Alaska Department of Labor and Workforce Development documented over 120,000 Alaska Native people in Alaska. While the majority of Alaska Natives live in small villages or remote regional hubs such as Nome and Bethel, the percentage who live in urban areas has been increasing.
In 2010, 44 % lived compared to 38 % in the 2000 census. The modern history of Alaskan natives begins with the arrival of Europeans. Unusually for North America it was the Russians, coming from Siberia in the eighteenth century, who were the first to make contact. British and American traders did not reach the area until the nineteenth century, in some cases missionaries were not active until the twentieth century. Arriving from Siberia by ship in the mid-eighteenth century, Russians began to trade with Alaska Natives. New settlements around trading posts were started by Russians, including Russian Orthodox missionaries; these were the first to translate Christian scripture into Native languages. In the 21st century, the numerous congregations of Russian Orthodox Christians in Alaska are composed of Alaska Natives. Rather than hunting the marine life, the Russians forced the Aleuts to do the work for them; as word spread of the riches in furs to be had, competition among Russian companies increased and they forced the Aleuts into slavery.
Catherine the Great, who became Empress in 1763, proclaimed good will toward the Aleut and urged her subjects to treat them fairly. The growing competition between the trading companies, merging into fewer and more powerful corporations, created conflicts that aggravated the relations with the indigenous populations. Over the years, the situation became catastrophic for the natives; as the animal populations declined, the Aleuts too dependent on the new barter economy created by the Russian fur trade, were coerced into taking greater risks in the dangerous waters of the North Pacific to hunt for more otter. As the Shelikhov-Golikov Company and Russian-American Company developed as a monopoly, it used skirmishes and systematic violence as a tool of colonial exploitation of the indigenous people; when the Aleut revolted and won some victories, the Russians retaliated, killing many and destroying their boats and hunting gear, leaving them no means of survival. The most devastating effects were from disease: during the first two generations of Russian contact, 80 percent of the Aleut population died from Eurasian infectious diseases.
These were endemic among the Europeans, but the Aleut had no immunity against the new diseases. Geopolitical reasons drove the Tsarist government to expand into Indigenous territory in present day Alaska, spreading Russian Orthodoxy and consuming the natural resources of the territory along their way, their movement into these populated areas of Indigenous communities altered the demographic and natural landscape. Historians have suggested that the Russian-American Company exploited Indigenous peoples as a source of inexpensive labour; the fur trade led the Russian American Company to not only use Indigenous populations for labour, but to use them as hostages to acquire iasak. Iasak, a form of taxation used by the Russians, was a tribute in the form of otter pelts, it was a taxation method the Russians had found useful in their early encounter with Indigenous communities of Siberia during the Siberian fur trade. Beaver pelts were customary to be given to fur traders upon first contact with various communities.
The Russian American Company used military force on Indigenous families as they were taken hostage and held until the male community members brought forth furs. Otter furs on Kodiak Island and Aleutian Islands enticed the Russians to start these taxations. Robbery and maltreatment in the form of corporal punishment and the withholding of food was present upon the arrival of fur traders. Catherine the Great dissolv