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The Physical World of Mountains
Bare, jagged rocks and show-capped peaks shining brilliantly against a clear blue sky
create scenery as dramatic as any the Earth can offer. Mountains inspire us with their
beauty. They also remind us of the huge forces that can crumple the surface of the Earth
as though it were made of paper, thrusting up mountains miles high in ranges thousands
of miles long.
The Earth is composed of several layers with a common center. Soil and rocks form the outermost skin of
the solid Earth, but they form only a thin layer, called the crust. Beneath the crust lies the mantle,
composed of hot, semi-molten rocks, and below that a liquid outer core encloses a solid inner core made
from almost pure iron.
It is only at the surface that the Earth is cool. If you were to drill a hole vertically into the crust, the
temperature would increase with depth. Miners deep below ground, therefore, work in a warm
environment. The rate at which the temperature increases with depth is called the geothermal gradient
(geothermal describes the heat on the inside of the Earth). This varies from place to place, averaging about
870 for every mile of depth. Almost all the warmth is produced by the decay of radioactive elements in the
rock.
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Continental and Oceanic Crust
The crust that lies beneath continents is called continental crust and is on average 25 miles thick. Its upper
part consists of rocks with an average density of about 166 pounds per cubic foot. Below these, in the
lower crust, the density increases to about 187 pounds per cubic foot.
The oceanic crust, beneath the oceans, is more complex. It consists of four layers, the uppermost layer
consisting of sedimentary rock, a type of rock formed within bodies of water as organic material and
minerals slowly deposit on the bottom. This rock varies in thickness from 3 to 6 miles. The density of the
rocks in the three lower layers is similar to that of the lower continental crust, about 187 pounds per cubic
foot.
The Mantle
The mantle is about 1800 miles thick and is made up of several layers. The uppermost part is solid.
Molten rock of the upper mantle mixed with molten rock from the base of the crust is called magma.
When it reaches the surface through volcanoes, it solidifies as lava. Below that there is a transition zone in
which the density increases, leading to the lower mantle. This extends to the boundary of the Earth’s core.
A Section Through The Earth: The solid rocks at the surface of the Earth form a thin crust beneath
which lies the mantle, a much thicker layer of hot, semi-molten rocks. Below the mantle the liquid outer
core encloses a solid inner core made from almost pure iron.
The Core
The outer core is made not from rock but from iron mixed with sulfur. It is liquid and about 1,150 miles
thick. Within the outer core lies the inner core, which is solid and made from almost pure iron. It is a
sphere with a radius of about 1000 miles and its temperature is about 10,800 0F.
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The Formation of Mountain Ranges
There is more than one way to form a mountain. One such way is a result of continents moving upon the
surface. As a plate made from oceanic crust is dragged below a lighter, more buoyant, continental plate, its
rocks enter the hot core, where they melt. It is not a smooth, gentle process. The rocks fracture, and the
cracks fill with sediments and water; these are also carried into the warmer layers. The subducting rock
fractures the overlying rock, the water vaporizes and expands, and volcanoes form on the ocean floor
behind the region where rock is being subducted.
Magma also moves upward through cracks beneath the continental crust, forming volcanoes on the
landward side. Sedimentary rocks that have formed above the hard rock of the oceanic crust are pressed
against the edge of the continental crust. These pile up as a jumbled mix, which can be raised to a
considerable height.
Mountains
are formed
by volcanic
activity at
plate
margins.
A volcano is an opening at the surface of the Earth through which magma sometimes flows. Magma is not,
molten rock from the mantle. When it cools and solidifies, it is called lava. Volcanoes are not necessarily
shaped like mountains. Magma can seep gently to the surface and spread widely, solidifying as a
horizontal sheet. The height and shape of a volcano depend on the material from which it is made. Lavas
are not all of the same composition, and volcanoes eject rocks, ash, and gases as well as molten rock. The
highest volcanoes are made from alternating layers of lava and rock debris.
“Shield” volcanoes are not usually so tall and have sides that slope more gently. They are made from very
runny lava that flows a long way before it hardens. Mauna Kea and Mauna Loa, in Hawaii are shield
volcanoes.
Lava may also form a dome. A lava dome volcano can reach a considerable size. One of the largest is
Lassen Peak, in California. Its base has a diameter of about 2 miles, and it is more than 2,000 feet tall.
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The Natural World of Mountains
Towering mountains topped with snow create a skyline of breathtaking beauty, but the
picture tells only part of the story. Mountains are not simply bare rock. Many plants and
animals live on them, yet they are often different from those on the plains at the foot of
the mountain range.
Temperature and Height
Mountains in tropical or subtropical regions can be snow-capped because the air temperature decreases
with increasing height. Mountaineers climbing in the Himalayas or the central Andes set out in warm
temperatures surrounded by lush vegetation. As they climb, the weather becomes steadily colder, and they
must put on warmer clothes.
Air can be compressed, and it also has weight, so air at a low level is compressed by the weight of the air
above it, all the way to the top of the atmosphere. Compression forces molecules closer together. When
molecules are closer they collide more often causing them to gain energy. This additional energy raises the
temperature of the air; compressing air therefore makes it warmer.
The opposite is also true. Air pressure decreases with increasing altitude because there is less air pressing
down. As the pressure decreases, molecules move farther apart and lose energy, and the air grows cooler.
The rate at which the temperature falls is called the lapse rate. This averages 3.50F per 1,000 feet.
Mountain Environmental Zones and the altitudes at which they occur around the world. The Alpine
zone is generally above 13,000 feet and above. Sub-alpine generally starts above 9,800 feet. Montane
forest begins at 6,600 feet.
Changing Vegetation With Elevation
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At each level of the mountain, plants that are suited to the temperature and rainfall at that level are found.
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In middle altitudes, broad-leaved forests, with such trees as oaks and maples appear. In northern
regions like Canada and Scandinavia the forests would be coniferous. (composed of trees that bear
cones, such as firs and pines).
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Further up the mountain the type of forest changes. Trees are decorated in mosses and surrounded
by ferns. These forests tend to be shrouded in mist because they are higher than the base of the
clouds. This is often referred to as “mossy forest” or “cloud forest.”
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Still higher is “Elfin woodland” where winds are stronger. Wind dries out the growing tips of
trees, stunting their growth. The trees are small and twisted into curious shapes. Trees also tend
to become widely spaced and scattered.
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Higher we encounter “Timberline.” There are no more trees, summers are so short that the
needles of coniferous trees cannot mature, so the first frost of winter kills them. Spring frosts kill
the leaf buds of broad-leaved trees such as beech and ash. Trees cannot grow.
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Above tree line are meadows of grasses and wildflowers, with occasional small shrubs. This is the
“Alpine zone” where the vegetation resembles that of an alpine meadow. It also resembles
tundra, and like the tundra, it ends where it meets the land of permanent snow. Grasslands in
mountain regions will contain far more species than a true tundra.
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Alpine plants tend to have attractive flowers and are small in size. Mountain herbs cannot tolerate
being shaded by trees, so they grow beyond the tree line. There the summers are cool and short,
the winters long and cold, and the growing season does not last long.
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Mountain plants have to use water very economically. Rain may fall heavily on one side of a
mountain, but the other side is usually dry. Even on the wet side it is not always easy for plants to
absorb water. Steep slopes mean that water will run from the surface quickly.
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Many plants shelter from the wind by growing close to the ground or in crevices, often forming
“mats” which cover the ground. These low growing plants are sheltered from the wind by nearby
rocks and also cover a wider area of ground, reducing the rate at which water evaporates from the
ground.
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High in the mountains the air is thinner than it is lower down, and the sunlight is more intense.
Mountain plants take advantage of this to grow rapidly during warm weather. Their dark leaves
absorb the infrared radiation (heat) from the Sun, so the plants are often a little warmer than the air
around them.
Mountain Animals
Many mountain animals are migratory, not that they travel great distances like those on the plains and
grasslands, but they change elevation. Many will climb during summer to take advantage of the short but
intense growing season and will move to the lower elevation in order to avoid harsh winter conditions when
food would be scarce.
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Mountain Goat (Oreamnos americanus) both male and female mountain goats have beards, short
tails and long horns. Feet are well suited for climbing steep, rocky slopes, sometimes with pitches
of 60 degrees or more, with inner pads that provide traction and cloven hooves that can spread
apart as needed. Also, the tip of their feet have dewclaws that are sharp to keep them from
slipping. They are largest mammals found in high altitude of 13,000 feet or more. Herbivores
that live 15 years producing one “billie” each year, usually on an isolated ledge.
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Bobcat (Felis rufus) will hunt anything from insects to deer though they prefer rabbits and hares.
Bobcats follow very predictable patterns of behavior. Start hunting 3 hours before sunset until
midnight and will cover a route of about 7 miles, and then again from dawn until 3 hours after
sunrise. They stick to well-defined territories, which are marked with feces, urine and by clawing
prominent trees in an area. Range averages about 8 square miles or more
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Mountain Lion (Felis concolor) also known as a Cougar is a large solitary cat. Prefer habitats
with dense underbrush and rocky areas for stalking. Very territorial prowling 100 mile area, they
hunt deer, elk, moose, bighorn sheep and small rodents, which they kill with a suffocating bite of
the neck. Oregon has 5000 cougars. Most active at dawn and dusk back legs are large allowing
great leaping and short-sprint ability.
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Golden Eagle (Aquila chrysaetos) dark brown bodies with lighter golden-brown wings and heads
are birds of prey with a wingspan of 7 feet. Use their speed and sharp talons to snatch up rabbits,
birds and fish. Golden Eagle pairs maintain a 60 mile range and are monogamous, mating every
year for life. Talons used for killing prey and beak is used only for eating. Excellent eyesight,
often hunt in pairs where one birds drives prey toward they other. National bird of five nations,
Albania, Germany, Austria, and Mexico as well as the U. S.
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Alpine Marmot (Marmota marmota) lives between 4,000 to 10,000 foot elevation found mostly in
Europe. Diet consists of grasses, herbs, insects, spiders and worms. Not suited to warm
temperatures, they live in burrows and only emerge in early morning and late afternoon. They
consume large amounts of food to produce fat as they may go into hibernation when temperatures
are warm. They live up to 18 years and produce litters of up to 7 babies.
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Bighorn Sheep (Ovis Canadensis) named for the large horns on both males and females, which
weigh up to 200 pounds. Herbivores adapted to climbing steep terrain where they seek cover from
predators such as mountain lions, golden eagles, and coyotes. They live in large herds but do not
have a dominant male leader. During mating season or “rut” rams establish a mating hierarchy
for access to ewes by clashing horns
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Gorilla (Gorilla gorilla) the largest living primate they are ground dwelling and predominantly
herbivorous and live in tropical mountain habitat between 7,000 to 14,000 feet of elevation.
Males reach 450 pounds and have similar blood types and fingerprint patterns as humans. Living
to 50 years of age, males will leave group at age 11 and wander for around 5 years attracting
females until they have enough to settle and establish a territory. Highly intelligent, comparable to
a high school freshman.
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Giant Panda (Ailuropoda melanoleuca) scientific name literally means ”cat-foot black and white.”
A bear native to China, though a carnivore its diet is 99% bamboo and 1% honey, eggs, fish and
shrubs. Their digestive system is still that of a carnivore, therefore , they get very little nutrition
from bamboo which they consume at a rate of 30 pounds per day. This low energy diet explains
their limited activity and social interaction. A 2006 study found about 3,000 still living in the wild
and 239 living in captivity. Paw consists of a thumb and five fingers, which aid in holding and
eating bamboo. Pandas never establish permanent dens and never hibernate
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Chinchilla (Chinchilla lanigera) live in burrows or crevices in rocks, they are native to the Andes
mountains in Chile where they are about the size of a ground squirrel and are rodents. They are
agile jumpers (to 6 feet) they are hunted by birds of prey, snakes, felines and canines. Defense
mechanisms include spraying urine and releasing fur if bitten. Mostly herbivores they will take
insects. Litters are predominately twins and are born fully furred and with eyes open. Chinchillas
lack the ability to sweat and are easily overcome by heat stroke if exposed to temperatures over
800F for any length of time.
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Mountain Goat
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Bobcat
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Golden Eagle
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