An Introduction to Mountains
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“Any part of a land mass which projects conspicuously
above its surroundings” (Webster’s Dictionary)
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Definitions of Mountains
Importance of Mountains
Attitudes Towards Mountains
Mountains in Physical Geography
The Alpine Treeline Ecotone
Theoretical Frameworks for Studying Mountains
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Definitions of Mountains
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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
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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
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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
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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
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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
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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
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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
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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
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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 (4070), 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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