Appalachian. General Characteristics.
The Appalachian system extends from the northeast to the southwest over 2000 kilometers within Canada and the United States. Crossing its main part of the southern half of the temperate zone, in the south enters the subtropics. It is characterized by medium-altitude relief, significant erosion dissection, an abundance of minerals, water resources, as well as forests rich in species composition. The foothills of the Appalachians are densely populated, their natural landscapes are significantly modified by man.
Rivers crossing the mountain system are important paths connecting the interior of the United States with the Atlantic coast. In the north, the Appalachians are adjacent to the Gulf of St. Lawrence, and the ridges of these mountains enter the Gaspé and Nova Scotia peninsulas. They are separated from the Laurentian Upland by the wide valley of the St. Lawrence River. The Rdirondak Mountains, located between the St. Lawrence Valley and the Lakes of Ontario, also belong to this part of the Appalachians. By structure, they belong to the Canadian Shield, but throughout the whole complex of landscapes – to the northern Appalachians.
1. Physical and geographical zoning
The Appalachians are located in the east of the mainland North America. In the north, the mountains border the Laurentian Upland, the Central and Great Plains skirt from the west, and in the south, their border runs along the Coastal (Mexican and Atlantic) lowlands. In the east, the Appalachian Mountains are washing the waters of the Atlantic Ocean.
2. Tectonic structure
The Appalachians are ancient mountains, rejuvenated by modern tectonics. The formation of geological structures – Caledonian and Hercynian – and the emergence of modern forms are separated by a long period of time. Long-term denudation exposed the roots of the ancient folds, so there is an amazing dependence of landforms on the lithological composition of rocks. The influence of river erosion and glaciation on the relief (and directly or indirectly) on other components of nature is clearly visible.
A single orographic area consists of two areas: the Northern and Southern Appalachians, separated by depressions – Kohok Hudson and the Hudson Champlain.
The northern Appalachians, composed of crystalline rocks, are low, glacier-smoothed and covered with coniferous forests. By the nature of the landscape, they are close to the southern heights of the Canadian Shield. A significant part of them is a hilly plateau, and only in the south and southwest the territory has a mountainous character. Denudation, continuing from the Lower Paleozoic, removed the surface layers, revealing the core of the Caledonian folds of gneisses, schists, granites and other dense rocks. Large relief forms are due to block tectonics, which appeared later on Caledonian folding. There is no clear correspondence of large relief forms to ancient folded structures. The modern relief took shape in the meso-Cenozoic in the process of slowly raising the territory. Along with the Caledonian, areas of neighboring structures were raised, such a site is the Adirondack mountain range, which is part of the Canadian Shield. However, it is similar in geomorphological and other features to other areas of the Northern Appalachians. In the east, the ranges reach the ocean and form peninsulas divided by bays (rias type of coast). The largest of them – the Bay of Fundy – is known for the highest tides in the world (up to 18 meters).
The southern Appalachians, consisting of Caledonian and Hercynian structures, are composed of variegated rocks and have a diverse structural-erosional relief. They were not exposed to glaciation: the rich pre-glacial forest flora was preserved.
Three structural zones are distinguished: an ancient crystalline complex of rocks (continuation of the structures of the Northern Appalachians), structures of Hercynian age, and horizontally-lying sedimentary rocks (part of the North American platform). Belts in the meso-Cenozoic were involved in uplift. The amplitude of the uplift was not the same, which was especially pronounced within the first belt, where two types of relief appeared: in the most elevated part – mountainous (Blue ridge up to 2100 meters high), in the less elevated eastern part – Piedmont plateau with an inclined surface from 500 to 150 meters high.The belt of the Hercynian structures is expressed in relief by the alternation of wide valleys and ridges. The bottom of the valleys are usually at an altitude of 300 meters, the ridges reach 1200 meters in height. This is the most interesting geomorphologically part of the Appalachians with a pronounced fold-erosion type of relief. Surface shapes do not show direct correspondence to the structure. Wide valleys elongated in the direction of bedding (the largest of them is the Big Valley), formed not along discharge lines or syncline structures, but in the places of development of the most pliable erosion of rocks, mainly in limestone and dolomite. The ridges separating them, as a rule, are composed of more dense rocks, most often sandstones. Their forms are associated with the occurrence of seams. Often, you can observe relief inversions, i.e. inconsistency of relief and structure: usually, as depressions formed at the site of diffuse cores of anticlines, as well as positive forms associated with the prepared erosion by the layers lying in the synclinal fold.
To the west of the Hercynids lies the Appalachian Plateau – the edge of the North American Platform, raised simultaneously with the Appalachians. The horizontal occurrence of sedimentary layers causes lithological homogeneity, as a result of which selective erosion has not been developed here. The predominant type of valleys – deep antecedent cuts – gorges. The plateau reaches 1,200 meters in height and in some places is so much dismembered that it has a typical medium-mountain relief. Limestone outcrops led to widespread karst development.
The height of most of the Northern Appalachians does not exceed 1,000 meters, only individual peaks of the Adirondak Mountains rise above 1,600 meters, and Mount Washington in the White Mountains range reaches 1,916 meters. Most of the area is a hilly plateau 400 – 500 meters high with erosion-residual relief. The Northern Appalachians were covered with ice, and their relief is characterized by finite-moraine ramparts, the trough profile of the valleys, numerous waterfalls on the rivers flowing in the hanging valleys, and glacial lakes.
Gradually falling Appalachians closely approach the coast of the Atlantic Ocean. The flooding of the dissected surface of the peneplain created an exceptionally diverse coastline with a multitude of islands, peninsulas, flooded river estuaries and bays in which large and small port cities are located (Boston, etc.). At the mouth of the Hudson River and on the coastal lowland island of Long Island is the largest city and port of New York.
Southern Appalachians represent the outskirts of the mountain system, which encircled the edge of the North American platform from the south. In the formation of the modern relief of the Southern Appalachians, the main role belongs to the erosion processes, which completely transformed the initial relief and led to its inversion.
From the west, the Appalachians are limited to a high (1,000 meters or more) piedmont Appalachian Plateau, corresponding to the Pre-Appalachian Trough, which is filled with sedimentary rocks containing rich mineral resources.
The plateau is tilted from east to west and deeply dissected by the river valleys of the Ohio Basin. In the west it breaks off to the neighboring plains, and in the east it rises and in the highest part is called Allegana. The next, more eastern zone, is a system of longitudinal ridges and valleys separating them with a characteristic Appalachian structure. As a result of erosion of the anticlinal ridges, composed of loose rocks, in their place formed longitudinal valleys. The most blurred and lowest of them is called the Big Valley. The synclines, composed of more erosion resistant rocks, prepared by erosion and expressed in the relief of plateau ridges, however, even the highest points of this zone are much lower than the edge of the Appalachian plateau and the ridges lying to the east.
The next highest zone of the southern Appalachians is a system of ridges composed of crystalline rocks of the Lower Paleozoic with sharp asymmetrical crests with steep eastern slopes.In this zone, in the so-called Black Mountains, the highest mass of the Appalachian Mountains – Mitchell (2037 meters) rises and the watershed between the Atlantic Ocean and the Mississippi Basin.
The rivers of the Mississippi Basin have a characteristic stalier structure of the valleys: gorge-like transverse sections that cut through the ridges alternating with segments of wide valleys occupying anticlinal longitudinal positions.
In the far east, the Appalachian system is limited to a low (no more than 400 meters) crystalline Piedmont plateau, which rises above the Atlantic plain. Here is the famous “line of waterfalls” with its huge, intensively used water resources.
South of New York, flooded river mouths, transformed by sinking into broad sea bays, penetrated deep into the continent to the foot of the Piedmont Plateau and dismembered the coastal plain into peninsular areas that were not closely interconnected. Due to such features of the coastline, the largest cities in the area, spread out at the foot of the Appalachians, are at the same time large ocean ports. An example would be Philadelphia on the Delaware River, 160 kilometers from the ocean, Baltimore on the shores of the Chesapeake Bay, Washington in the lower reaches of the Potomac. On the sandy Atlantic coast, full of spits and lagoons, resort towns with comfortable beaches are located.
3. Inland waters
North America is rich in inland waters. By the sum of the annual runoff (331 mm), it is second only to South America. However, in many parts of North America there is a shortage of fresh water, especially natural and clean. This is due to both the uneven distribution of water resources and the peculiarities of their use.
Rivers of North America have enormous energy resources, much of which is mastered. Many rivers and lakes are of great transport value. Natural waterways complement the network of canals connecting the largest water systems.
The water balance features (in comparison with other continents) reflect the nature of the continental topography, and, above all, the presence of mountain systems that contribute to heavy precipitation (805 mm on average for the continent) and the rapid flow of water. Along with the relatively small size of areas of dry and arid climate, where large evaporation water losses usually occur, this factor causes a relatively high coefficient of water flow. The distribution of water flow is very uneven. The greatest height of the drainage layer for the Appalachians is 400-600 mm.
The regime of the rivers of North America has a number of specific features. Firstly, the glacier regime of the rivers, especially in the large glacial regions of the Arctic, is wider and fuller than in foreign Eurasia. Secondly, in North America, types of rivers with mixed snow and rain feed are very diverse. This diversity is due to significant fluctuations in the thickness and duration of the occurrence of snow cover.
The rivers flowing from the Appalachians are short, but they are deep and fast. Crossing the steep edge of the foothill plateau, almost all the rivers form waterfalls. Most of the rivers of the southeastern coast end at the Atlantic Ocean with large estuaries and are accessible in the lower reaches for ocean vessels. The most significant of them – Hudson, Delaware, Susquehanna and Potomac. For the most part of the year, the left tributaries of the Mississippi have considerable reserves of water energy, the Ohio with the Tennessee tributary having the largest reserves.
The western slope of the Appalachians, most of the Central and Great Plains belongs to the Mississippi River Basin. The river has a predominantly snow-rain regime, due to the diversity of climatic conditions, the western and eastern parts of the river basin are very different in hydrological features. The right tributaries, descending from the Rocky Mountains, flow through arid territory, cut deep into the surface of the Great Plains, carry a large amount of suspended sediment and relatively little water. That is why even after the merger with Missouri, Mississippi remains relatively shallow. It becomes a big river only after the confluence with the Ohio Mississippi River increases water consumption only 1.5 times. That is why its mode in the lower reaches is largely determined by the regime of the Ohio River. If the snowmelt period in the Appalachians coincides with the maximum precipitation, the water level in Ohio rises by 15–20 m, in the lower Mississippin, 5–6 m. This leads to the flooding of a significant part of the floodplain. Mississippi spills contribute to the features of its valley. Already in the area of confluence with the Ohio River, the Mississippi begins to postpone alluvium, which is mainly carried out by right tributaries. When flowing into the ocean, it forms one of the largest alluvial lowlands on the globe and an extensive fast-growing delta. Breaking into numerous channels bordered by coastal ramparts, the river strongly meanders across a marshy flood plain. In flood, it often overflows. Blurring the coastal ramparts, floods the upper floodplain, sometimes on the area up to hundreds of thousands of square kilometers. Mississippi is a convenient military route from the Gulf of Mexico to the central parts of the mainland and an important reserve of hydro resources.
Rivers crossing the mountain system are important paths connecting the interior of the United States with the Atlantic coast. Abundant precipitation feeds a dense hydrographic network. Of particular importance is the Hudson River, flowing through the tectonic depression of the trough-shaped form.Maintaining the quality of surface and to a large extent groundwater is one of the pressing problems of the United States, where 460 billion m3 of fresh water is used annually. The total length of polluted drains exceeded 120 thousand km, many lakes are heavily polluted. Pollution of water bodies with particulate matter occurs primarily during the erosion of agricultural land. Waste products make up more than half of the solid runoff of rivers, especially the Appalachian and Great Plains rivers. Excess nitrogen and phosphate fertilizers are carried away from the fields along with solid particles. In rivers and lakes, they serve as nutrients for rapidly developing aquatic vegetation.
Another important source of pollution is technological processes in industry, especially the chemical and petrochemical industries. The water bodies of the northeastern United States, southeastern Canada and other areas suffer from these pollution. In 25 states of the USA, cases of poisoning of water bodies with salts of heavy metals contained in industrial effluents were recorded. Water bodies also suffer from the so-called thermal pollution, which leads to disruption of the oxygen balance in the water, a strong transformation, or even a change in the indigenous aquatic biocenoses. In a particularly serious problem, thermal pollution rises in the southeastern United States, where the temperature of water in the warm period of the year is already very high (+ 32 ° C).
The Appalachian Mountains are located in the temperate and subtropical zones. Over most of the mountains dominated by continental air, since the western transfer greatly limits the influence of the Atlantic Ocean. The role of the summer monsoon, coming from the Gulf of Mexico and also having a western and southwestern component, is significant.
The Appalachians are characterized by unstable weather patterns, sudden changes in temperature and a significant amount of precipitation during all periods of the year. The average January temperatures increase from -10 ° C in the north to 4 ° C in the south, and July – from 18 ° C in the north to 25 ° C in the south. The annual precipitation is 1000-2300 mm (due to mountain conditions it is subject to considerable fluctuations). In winter there are heavy snowfalls in the northern part, thunderstorms in summer. The best time of the year is the beginning of autumn, the so-called “Indian summer”, when the days are not as sultry and hot as in summer, and less often there is rain.
The Appalachians are characterized by two main spectrums of vertical zones: the Continental-Tundra continental and the forest-meadow continental. Due to low altitudes, the bulk of the territory lies in the forest belt. Mixed forests prevail. The Appalachian highland is under the influence of the circulation coming from the Atlantic Ocean and the masses of continental air that form over the inner parts of the continent. Annual precipitation ranges from 1000 mm in the north to 2000 mm in the south. The abundance of moisture creates favorable conditions for the development of the water network, and where this contributes to the relief, for waterlogging the area.
The climate of the Northern Appalachians is about 40 ° North latitude is severe, with fairly large variations in temperature over the seasons, which is largely determined by the geographical position of this part of the mountains and the influence of the cold current. The average temperature of the coldest months in the area varies from -5 to -12 ° C. Rivers and lakes are covered with ice for the period from December to April. In winter, there is significant snow cover in the north. Summer is cool (the average temperature never reaches + 19 ° C.), Foggy and rainy.
To the south, the temperatures of summer and winter increase, but still the winter temperature is much lower than the average for these latitudes. In the mountains at an altitude of 600-700 meters, it is negative, and snow falls there. Summer is much hotter than in the north (the average July temperature is up to + 25 ° C), and more humid.
The differences in climatic conditions between the north and south of Appalachia are reflected in the nature of the land cover.
In winter, the radiation balance is negative. The land surface cools faster than the surface of the oceans, so the air entering the continent in the surface layer also cools and becomes more dense. As a result, the atmospheric pressure in the upper levels of the troposphere decreases. Isobar maps at an altitude of 5 km show a baric trough extending over the eastern part of the continent from a low-pressure area above the Arctic Ocean.
5. Soils, minerals, vegetation and wildlife
The nomenclature of soils in North America includes almost all the main soil types, characteristic of Eurasia.
In the north of both continents, tundra-gley, permafrost-taiga and podzolic soils are widespread. In more southern latitudes, they turn into sod-podzolic and brown forest (in a mild, humid climate). In the subtropical zone, a large amount of territory is occupied by yellow and red soils, as well as brown and gray-brown soils and gray soils.
For the Appalachians, mountain podzolic and brown forest predominate among the soils, and on the bottoms of the valleys – very fertile sod-calcareous soils.
The Appalachians are known for large mineral deposits. Coal, oil, iron, copper, silver, cobalt and other ores are mined here.
Similarity with Eurasia is also evident in the vegetation cover of North America. The tundra, forest-tundra and taiga formations of both continents essentially belong to the same zones, as if encircling both continents. However, the unity of the south is broken.
The ancient flora of North America has been preserved in the southern parts of the Appalachians (in deciduous forests), in the southwest (in coniferous forests), and in deserts. The existence of ancient and independent centers of the formation of floras caused a large species diversity (more than 30,000 species) and a significant number of endemic relict species in the flora of North America. The largest number of relics is known in the areas of California (sequoia, pseudotsura, cypress) and Appalachian (magnolia, tulip tree) floristic centers. A large number of plants, preserved from the Paleogene, allows us to consider these forests among the oldest in the northern hemisphere.
The Appalachians are characterized by two main spectra of vertical zones: the continental forest-tundra and the continental forest-meadow. Due to low altitudes, the bulk of the territory lies in the forest belt. Mixed forests prevail. One of the classic variants of deciduous forests, formed by dozens of chestnuts and oaks, as well as maples, beeches, etc., is associated with the concept of the Appalachian Forest.
The dense forest overgrown with vines is especially attractive in the “Indian summer”, when the foliage acquires a calm golden and reddish-yellow color. Forests were badly affected by logging and no longer preserved in the valleys.
At an altitude of 700-1000 meters coniferous species are mixed with broadleaf species. In this belt, sugar maple, yellow birch, black spruce and hemlock are more common. The spruce-fir forest (balsam fir with an admixture of thuja) dominates even higher, from about 1500m, and subalpine meadows and shrubs (rhododendron and alder) are on the highest peaks. North of 41 north latitude the lower zone of the deciduous forest wedges out. The mountains are dominated by a typical coniferous forest, but along the coast many broadleaf species reach Newfoundland.
At 42 north latitude typical representatives of Appalachian deciduous forests appear – plane trees, beeches, linden trees, and further south – tulip tree, chestnut and walnut. Broad-leaved forests climb into the mountains not higher than 600 m, and then are replaced by mixed forests. Coniferous forests are preserved only on mountain tops and in the most damp and shady places. The mountains almost never rise above the forest boundary. Thick, rich in composition relict Appalachian forests, by the time Europeans arrived on the mainland, covered the entire southern part of the Appalachians. The abundance of vines and evergreens gave them a real subtropical look. These forests served as a refuge and livelihood for many hunting tribes of Indians, including the tribe of the Indians of the Appalachians, who gave the name of the Appalachian mountain system.
At present, the forests of the Southern Appalachians are very sparse, and in many areas completely reduced. In the foothills, almost everywhere, the cultural landscape dominates with very small remnants of the former rich vegetation.In the Atlantic areas covered with glacier sand, and in some places with clay, in former times pine trees grew in the south and spruce forests in the north. Currently, these areas are also densely populated and have largely changed their natural landscape. But in some places on the coast there are still areas covered with pine forests. They are used as resorts and holiday homes.
Most of North America is zoogeographically close to Eurasia and falls within the Holarctic zoogeographic region. This similarity can be explained by the recent existence of a land connection between Northeast Asia and Northeastern America. But since North America is currently isolated from Eurasia, animal forms that are absent in Eurasia have taken shape on its territory, and at the same time there are not many forms characteristic of the latter.
Of the large land mammals of the tundra, the musk ox, or musk ox, is a strong, massive and very hardy animal. Currently, it can be found only on the Arctic islands of America and in Greenland. American caribou reindeer are much more common, belonging to the same species as the Eurasian wild reindeer, and represented by two races – the tundra and the forest. A polar bear is found along the northern coasts of the mainland and in the ice zone. Arctic wolf and polar weasel are also common in the tundra. Arctic fox is of great commercial importance. Lemming, hare and vole mice are widely represented among rodents. Of the birds wintering in the tundra, the most typical are the white and tundra partridges Of migratory birds, the Alaskan plantain, the white owl and various waterfowl nesting near lakes and swamps are found. There are a lot of fish in inland waters (lake trout, whitefish, grayling, etc.)
The fauna of the coastal waters of North America is rich. The Greenland whale, white whale and narwhal are still found. Numerous seals, walruses.
The taiga fauna is characterized by a much greater variety. The largest animal in the past was the wood buffalo, but now it is preserved only in reserves. Everywhere, moose is common, feeding on leaves and young shoots of trees and shrubs, as well as aquatic vegetation. There are numerous predators, most of which are valuable fur-trade animals: the northern skunk, the otter, the North American marten, or the American sable, the American mink, and the weasel. Among large predatory animals, bears (brown and black American), wolves, lynx, and wolverine are characteristic.
Canadian beaver and muskrat muskrat are the most typical rodents. These valuable fur-bearing animals were completely exterminated in many areas, but as a result, hunting restrictions have again spread. Interesting is the endemic iglosherst, or porcupin, a large rodent from the family of porcupines living mainly in trees. The igloshersta is hunted for its fur and meat. Of the smaller rodents should be called red squirrel, American hare, chipmunk and mice.
The fauna of mixed and deciduous forests is close to the taiga fauna, but there are some animals that are unknown in the taiga forests. In the deciduous forests there is a black baribal bear, characteristic of taiga. Like in taiga forests, wolves, foxes, minks, otters, raccoons, skunks, and American badgers are common. The characteristic hoofed of deciduous forests is the virginian or white-tailed deer, a relative of the European red deer.
Some representatives of the reptile fauna are characteristic – the Mississippi alligator and the Mississippi alligator turtle. Of amphibians interesting frog – bull, reaching 20 cm in length.