An Introduction to Mountains. “Any part of a land mass which projects conspicuously above its surroundings” (Webster’s Dictionary) Definitions of Mountains Importance of Mountains Attitudes Towards Mountains Mountains in Physical Geography The Alpine Treeline Ecotone
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An Introduction to Mountains • “Any part of a land mass which projects conspicuously above its surroundings” (Webster’s Dictionary) • Definitions of Mountains • Importance of Mountains • Attitudes Towards Mountains • Mountains in Physical Geography • The Alpine Treeline Ecotone • Theoretical Frameworks for Studying Mountains
Definitions of Mountains • Subjective: Mountains should be impressive, they should enter into the imagination of the people who live within their shadow, and they should have individuality (e.g., Mt. Fuji is benign and sacred, a symbol of peace and strength; Mt. Etna is a devil, continually sending out boiling lava and fire to destroy farms and villages). • Objective: Elevation, local relief, steepness of slope, and the amount of land in slope, dissected surface, structural origin, climatic and vegetation characteristics (i.e., ecology and topography are important); horizontal distances between ridges and valleys that establish the texture and framework for slope steepness; delimited by geologic criteria, in particular, faulted or folded strata, metamorphosed rocks. • Mountains are features of construction, they are built and produced by some internal force. But, they can also be built by destructive forces like erosion that gives mountainous character to a strongly dissected plateau.
Mountain Landscapes • High Mountain Landscapes: Alpine refers to a cold and windy zone above continuous forest, with rocky ridges and scattered tundra vegetation. The upper edge of the forest (the timberline) is generally lowest in the polar regions and rises in elevation toward the equator; timberline tends to rise from coastal areas toward the continental interiors. • Geoecological Approach: high mountains should rise above the Pleistocene snowline, the zone of rugged and serrated topography associated with mountain glaciers and frost action; should extend above the regional timberline; should display snow and ice processes such as frost-heaving and solifluction. High mountains are mountains which reach such altitudes that they offer landforms, plant cover, soil processes, and landscape characteristics.
Importance of Mountains • Mountains cover one-fifth of the Earth's land, and support ten percent of the Earth's population. • More than one-half of humanity relies on fresh water that accumulates in mountains. • Mountains are also globally important as a tourism and recreation resource. • Mountain peoples, with thousands of years of experience living and working in their rugged environments, are stewards of irreplaceable global treasures of cultural and biological diversity. • Especially in developing countries, they include some of the poorest people in the world, with little access to education, markets, and decision-making power.
Geomorphology • Most of the major mountain ranges are associated with plate boundaries and are uplifted as a result of plate collisions. Volcanic and seismic activity is also closely connected with mountain ranges. The process of mountain building arises from the movement of the earth’s crustal plates. The convergence of two or more plates causes buckling up of the intervening sediments and up thrusting to form upstanding relief. For example, the Himalayan arc, that was formed primarily around 30 millions years ago – hard core mountains beneath softer marine sediments and one the latter are stripped off by erosion I is these hard igneous masses which form the highest peaks. • Landscape of mountains, consisting of dissected and differentially eroded surfaces with abundant steep slopes and high absolute and relative relief, creates an environment of high energy that gives rise to high rates of erosion. Mountains are characterized by a preponderance of high magnitude, low frequency major landslides, earthquakes and floods. • Main processes consist of frost action, glaciers, fluvial and mass movements. Weathering is important, particularly in humid tropical environments with high temperatures and abundant water, and Aeolian processes tend to be restricted to summits and arid zones where vegetation cover is restricted.
Attitudes Towards Mountains • Today, mountains are almost universally viewed with admiration and affection. But that has not always been the case. • The Prehistoric Era: volcanoes and attitudes toward the fiery and destructive peaks were largely negative. Eruptions were interpreted as signs of the gods’ displeasure with the people, and so various cultures established elaborate taboos, ceremonies, and sacrifices to appease the wrath of the gods. Earthquakes often replaced volcanic eruptions as evidence of the violence and power of the gods who dwelled in the mountains and of their displeasure with mortals. • Primitive people often closely identified mountains with the weather – the home of storms, lightning, strong winds, cold, and clouds. Physiological reaction to mountains through high-altitude sickness.
Culture & Mountains • Mountains were also the home of great beasts – the Abominable Snowman of the Himalayas and Sasquatch (Bigfoot) of the mountains of western North America. But also mountains as something positive – givers of life since they were a source of water through rainfall and mountain streams. In Native American religion and imaginations, mountains were important – the Blackfeet Indians sang of “Going to the Sun Mountain” where the sun, a principal deity, made its home. • Perhaps the most spectacular display the world has ever known of human settlement in mountains is found in the Andes of South America – ancient Incas. • The Western Tradition: Mountains were objects of veneration and symbols of strength and peace to the Hebrews of the Old Testament – God often chose a mountain as the place to meet with one of his prophets – Mt. Sinai and Mt. Zion.
Classical & Medieval Times • Classical Heritage: Homer’s Illiad mentions mountains chiefly in contexts that evoke their wildness and isolation. They are the haunts of nymphs, wild beasts; the only men to frequent the lonely slopes are hunters and woodcutters. Mt. Olympus is the most prominent mountain in Greek mythology. • Medieval Fears: During the Middle Ages superstitions held sway, and mountains were considered no better than grotesque wastelands. Dante made mountains the guardians of hell. By the end of the 17th century, on the verge of the Enlightenment, publications began to appear which supported the idea of a purposefully designed earth and the uses of mountains – wildlife, minerals, scenery.
Far East Region & the Modern Period • The Far East: In Japan, China, Tibet, and India, mountains have long been adored and worshipped. Buddhism, Taoism, Confucianism, Shintoism, and Hinduism all incorporated mountains worship into their beliefs. In early Chinese culture, the mountain was considered to be the body of God, the rocks his bones, the water his blood, the vegetation his hair, and the clouds and mists his breath. • The Modern Period: Romantic adoration of mountains by arts and philosophers; science began studying the origin of mountains; tourist resorts sprang up and sanitariums were built to treat the sick.
Physical Geography of Mountains • Climate and Mountains: key influences on the nature and rates of geomorphological processes. Operates at different scales. Mountains can modify global atmospheric processes and generate their own climatic conditions thus affecting the climates of adjacent regions. Influences include latitude, altitude, continentality, and topography. • Latitude: affects solar radiation receipts, temperature, seasonality, and modifies the influence of altitude, causing treeline and snowline altitudes, and the occurrence of permanent snow and ice to descend polewards. • Pressure systems: Equatorial low pressure (0-20 N&S), Subtropical High Pressure (20-40), Subpolar Low pressure (40-70), and Polar high pressure (70-90). High pressure zones tend to be drier, whereas low pressure zones tend to be wetter. Seasonality and the day length vary from the equator to the pole. • Impact of latitude on solar radiation: concerns the height of the sun and the angle at which its rays hit the surface of the earth. Slope angle and slope aspect are therefore important. The influence of global circulation also contributes to precipitation.
Altitude, Position, & Barriers • Altitude: general trend with increasing altitude is a reduction in temperature, air density and pressure, proportions of carbon dioxide, water vapor and concentrations of impurities such as dust. The intensity of solar radiation, and especially the UV component, increases with altitude. • Continentality: distribution of land and sea in relation to the location of mountains is important. Oceans have the effect of moderating climate. Coastal mountains tend to be wetter and cloudier due to the effect of humid air blowing onshore and being forces up, thus giving rise to precipitation. Continental interiors tend to be more extreme with greater temperature fluctuations occurring more rapidly, drier conditions, less cloud and consequently higher solar radiation receipts. • Topographic and Barrier Effects: barriers and the importance of relief and mountain mass affecting air circulation.
Atmosphere & Mountains • Temperature: closely related to solar radiation – wet (3.2 F/1000ft) and dry adiabatic (5.5F/1000ft) lapse rates. Greater cloud cover of mountains compared with lowlands as a result of uplift and condensation enhances the effect of thinner air and reduced heat retention. • Precipitation: convectional and synoptic. The type and amount of precipitation depends on the moisture content of the air, the rate of ascent, wind speed, and degree of uplift; orographic precipitation. • Solar Radiation: thinner air at higher elevations causes rapid fluctuations in the response of temperature to changes in solar radiation. Affected by cloudiness, aspect and topography. Snow cover increases surface albedo, reduces the absorption of energy, and so affects total radiation receipts. Rapid cooling of air and surfaces causes an increase in relative humidity, less evaporation, more condensation, and fog. • Winds: occur at different scales; winds are either synoptic or thermally induced. Chinook winds on the Great Plains as air clears over the Rockies. Thermally induced winds, mountain and valley winds, and other more locally modified winds such as glacier winds.
Mountain Processes • High mountains are dominated by freeze-thaw, periglacial and glacial activity, intermediate slopes by erosion and deposition processes of glaciers and rivers as will as mass movements. • Glaciers: they reached their last maximum during the Quaternary period. The last glacial maximum ended around 14,000 years ago. • Fluvial Action: closely related to precipitation and to snow and ice melt and thus is variable in time and space. • Mass Movements: soil creep, mudflows, snow avalanches, debris flows, slumps • Mountain Soils: develop on summits from sediment collected in pockets and on slopes, anchored by vegetation and protected from high winds. They tend to be thin, stony and often low in nutrients and in need of improvement. Finer, deeper material accumulates in alluvial fans and in valley bottoms with a better developed A-horizon. Glacial tills provide the basis for many soils. In high alpine meadows, the development of dens meadow turf protects the surface as long as it remains intact. Excessive trampling or other surface disturbance can quickly lead to deep gullies once the turf mantle is broken.
Treeline & High Mountains • Treeline: most dramatic ecotone – krummholz (stunted tree). As a general rule, timberlines globally correspond with the 10 degree C July isotherm. • Meadows and Tundra: above the treeline the open meadows and tundra comprise a treeless plain, dominated by herbs and grasses and in some cases shrubs. • Wildlife: in poorly developed ecosystems, it’s advantageous for species to be more generalist in their habitat preferences to maximize options for survival. Faunas tend to be dominated by rodents, scavengers, and insects. Life resolves around an alternating life of feast or famine. Some larger mammals are well able to cope with hypoxia – lamas and alpaca. • Human Physiology: one of the most important parameters for determining stress to human biology is the fact that atmospheric pressure reduces with altitude and limits the oxygen-absorbing capacity of the blood. With the decline in pressure the process by which oxygen is bound into the hemoglobin in the bloodstream does not work so efficiently. This is known as hypoxia, normally encountered at 2500 meters at which oxygen stress can be clearly identified.
Snow, Glaciers, & Snow Avalanches • Snow – precipitation in the solid form that originates from freezing of super-cooled water around tiny nuclei of foreign matter, especially clay minerals, in the air. They grown through condensation, and diminish through evaporation; often a hexagonal pattern of the snowflakes. • Polar areas, sub-polar areas, and mid-latitudes & snow fall. • Behavior of fallen snow; densification through freeze-thaw and “firn” (i.e., dense snow at least 1-yr old). • Snowline – zone between seasonal snow that melts every summer and the permanent snow that does not melt each summer; regional snowline represents the minimum elevation where a glacier may form; generally lowest in areas of heavy precipitation.
Glaciers – Masses of Moving Ice • Mass of moving ice created by the accumulation of snow; transformation of snow into ice is a process of densification and expulsion of air, which is accomplished by sublimation, melting, refreezing, and compaction. • Firn is an intermediate stage ion the progress towards glacial ice. • Glacial retreat; height of the ice age was 1,000-yrs ago – cirque glaciers, ice-fields, valley glaciers, piedmont glaciers. • The Pleistocene represents 2.5 million years of major fluctuations in the environment; at least 4-major advances of ice. • We are now in an interglacial period, after the last major ice advance melted about 15,000 years ago.
More on Glaciers • The annual snowline or firn limit represents the maximum extent of summer melting.; from a mass balance perspective, it is the equilibrium line and the concept of steady state.; the equilibrium line marks the zone on the glacier where the mass of the glacier stays nearly the same during the year. • Periods of environmental change: following the final advance, a warm and dry period ensued (hypsithermal) that last from 4,000 – 10,000 years ago; the next major change was a widespread advance of mountain glaciers, 2000-4,000 years ago, followed by a warming trend of about 1,000 years, which was followed by a period of glacial advance during the “Little Ice Age” in the 17th and 18th centuries.
Glacial Movement • Determined by the thickness of the ice, its temperature, the steepness of the glacial surface, and the configuration of the underlying and confining topography. • In general, the greatest movement of the ice takes place in the center of the glacier and decreases towards the edges; longitudinally, greatest at the center and least at the head and terminus. • The area above the equilibrium line is the zone of accumulation, and the area below the line is the zone of ablation. • Glacier surges; move through plastic flow and basal sliding; water as a lubricant; abrasions and striations left on the bedrock are evidence of glacial movement.
Glacier Structure, Erosion, & Associated Landscape Features • Crevasse and tensional stress; increase efficiency of rock transport and hasten ablation, danger of snow-bridges, conspicuous features (e.g., lateral moraines, cirques, aretes, horns, U-shaped valleys, hanging valleys, patternoster lakes, and more). • Primary erosion processes are abrasion and plucking; upstream side of bedrock overrun by a glacier is smoother and gentle, while the lee-side becomes steep and irregular. • Erosional and depositional features. • Snow avalanches (loose snow and slab avalanches), avalanche triggers, snow avalanche paths, vegetation and geomorphic processes.
Mountain Vegetation • Mountains display the most rapid and striking changes in vegetation of any region on earth; they serve as pathways for plant migration, because they extend into areas of lower temperature and provide an environment more like that found near the poles. • Mountains act as barriers to the migration of species. • Isolated peaks often serve as mainland islands with many of the biogeographic characteristics of oceanic islands. • Migration is hindered to or from mountains, therefore, species have a limited gene pool that receives little infusion from the outside. • Adaptation becomes adjusted primarily to local conditions; evolution frequently results in the creation of species found only on the mountain (endemic).
Mountains & Vegetation Species • The number of plant species decrease with increasing elevation. • Tendency is toward smaller and less elaborate plants with slower growth rates, decreased productivity, decreased plant diversity, and less interspecies competition with increasing elevation. • The primary characteristic of mountain vegetation is the presence of sequential plant communities with increasing altitude. • Climax community is the culminating stage in natural plant succession – where a complex of species is so well adjusted to each other that they are able to reproduce and maintain themselves for long periods of time (e.g., centuries).
Mountain Forests • Consist of three dominant life forms – needle-leaf evergreen conifers, broad-leaf evergreen, & broadleaf deciduous. • Needle-leaf conifer grows primarily in middle and higher latitudes of the northern hemisphere. • Broad-leaf evergreens tend to be dominant in warm and humid regions with small temperature ranges. • Conifers dominant in the higher reaches of elevation and latitude (e.g., the boreal forest that stretches in an almost unbroken band across North America and Eurasia. • Photosynthesis as soon as conditions permit; no new leaves to grow.
Vegetation Forms • Mosaic of communities of different ages and compositions offer different habitats, but in the absence of fire the landscape becomes more homogenous. • Mountain meadows are generally maintained by either poor drainage, excessive fire, snow, or wind; meadow invasion by conifers due to environmental change. • Timberline is the transition from forest to tundra, one of the most dramatic ecotones on earth; suggests a transition from closed canopy forest to treeless tundra; upper limit of erect trees represented by scattered clumps of trees or isolated individuals; krummholz is the upper limit of stunted and deformed trees. • In general, timberlines are lower in marine locations and higher in continental areas; dominance of evergreen species and some deciduous.
More on Alpine Treeline • Patterns at treeline are characterized by different life forms, but a prostrate form is common; flagging, tree islands, ribbon forests separated by snow glades (occurring at right angles to the prevailing wind that tends to pile snow up in drifts; deep snow accumulation inhibits forest encroachment. • Causes of treeline – excessive snow, strong winds, poor or excessive drainage, lack of soil, recent disturbance; sunshine, high temperatures, and high degrees of ultraviolet radiation that can restrict tree growth; animals eat leaders, humans and fire (e.g., native Americans). • Inability of shoots to ripen when they freeze or dry out; most plants are perennials at the alpine tundra; most are evergreen and have large and extensive root systems; reproduction of tundra and alpine plants through pollination can be limited by the short growing season and late lying snow patches; plants can reproduce through rhizones, i.e., root-like stems that run out from the plant with the ability to send up new shoots.
Landforms & Geomorphic Processes • Mountains are rapidly worn-down (denudation) and can never be very old compared to the vastness of geologic time; erosion increases with increasing altitude. • The form, structure, and material composition of mountains greatly affects the rate and type of geomorphic processes. • The horizontal or vertical orientation of rock as well as the nature of the rock type have major impacts on landscape development. • Nivation is a combination of frost action and the downslope movement of earth material by gravity (mass-wasting) often resulting from the presence of snow patches; best developed at treeline and the narrow transition between the glacial and the periglacial environments.
Mass Wasting • Downslope movement of material due to gravity; creep is the slow movement; frost creep is the downslope movement as the result of frost heaving and settling upon thawing. • Solifluction (“to flow”) – essential elements include water, soil texture, slope gradient, rock type, and vegetation. • Mudflows is the massive failure of large sections of slopes and often confined to a definite channel, high speed of movement, up to several meters/second. • Conditions for mudflows: abundant water, land of stabilizing vegetation, unconsolidated material with enough fines to serve as lubrication, and moderately steep slopes. • Slumping (slippage of unconsolidated material); rockfall the falling of rock from a cliff or headwall; landslides and debris avalanches.
Features of Mass-Wasting • Talus is an accumulation of rocks at the base of cliffs, headwalls, or steep slopes; falling rocks come to rest to form a ramp or rock apron; also known as scree or a rock debris slope. • Talus slope is determined by the supply of material, movement of material within the talus, and removal of material. • Protalus rampart is an accumulation of rocky debris found near the base of a slope, but separated from it by a small trough or depression; best developed above treeline in shaded spots near steep rock walls or in cirques where there is ample rock material and where abundant snow accumulates and melts slowly; they resemble glacial moraines in that they occur as sinuous ridges. • Rock glaciers are accumulations of rocky debris with a form similar to that of true glaciers.
Some Theoretical Foundations • A Systems Approach • Hierarchy Theory • Complexity Theory • See the course outline for details.