Earth Science

13. z

24. What are the factors used to classify mountains?
-Mountains are classified on the basis of different factors
such as location, mode of origin, height and orogenesis.
Height: On this basis mountains are classified as high,
low, rugged and rough
Location: Depending upon the location of the mountains
they are classified as oceanic mountains, coastal mountains
and island mountains.
Orogenesis: On the basis of orogenesis factor the mountains are
classified taking into consideration the geologic period of its formations
such as the Caledonian mountains, Pre-Cambrian Mountains,
Hercynian Mountains, Varsican mountains and Alpine mountains. The
Pre-Cambrian Mountains are no more in existence as they have merged
with plains which are highly glaciated (Canadian Shield and Eastern
Scandinavia).

25. The Caledonian mountains have almost
become one with the plains but still
some of their existence can be seen in
Norway, Scotland, and New England.
Hercynian Mountains are the
mountainous terrains that are located in
the central European Highlands to the
north of Alps, the Applachians, Urals
(U.S.S.R.) and the mountains in the
north of Tibet.

44. Economic Values of Mountains
1. Mountains' greatest value may be as sources of
all the world's major rivers, and many smaller
ones (Mountain Agenda, 1998). Mountains play a
critical role in the water cycle by capturing
moisture from air masses; when this precipitation
falls as snow, it is stored until it melts in the
spring and summer, providing essential water for
settlements, agriculture and industries
downstream - often during the period of lowest
rainfall. In semi-arid and arid regions, over 90
percent of river flow comes from the mountains.

45. 2. Mountain water is also a source of
hydroelectric power, most of which is used on
the plains below. Historically, water wheels
have provided energy in mountain regions,
mainly for grinding grain. In rural Nepal there
are an estimated 25 000 water wheels and over
900 micro-hydropower turbines - a more
recent technology - that provide a critical
source of energy, mainly for agroprocessing
(Schweizer and Preiser, 1997).

46. 3. CENTRES OF BIODIVERSITY
Mountain ecosystems are globally important as
centres of biological diversity. The greatest
diversity of vascular plant species occurs in
mountains: Costa Rica, the tropical eastern
Andes, the Atlantic forest of Brazil, the eastern
Himalaya-Yunnan region, northern Borneo and
Papua New Guinea (Barthlott, Lauer and Placke,
1996). Other important centres are found in arid
subtropical mountains. Many of these areas with
the greatest biological diversity are designated as
national parks or other types of protected area.

47. 4. Mountain tourism; like a small hotel in the
Himalaya, Nepal
5. The Rocky Mountains are an important
habitat for a great deal of well-known wildlife,
such as elk, moose, mule and white-tailed deer,
pronghorns, mountain goats, bighorn
sheep, badgers, black bears, grizzly
bears, coyotes, lynxes, and wolverines. For
example, North America's largest herds of
moose is in the Alberta-British Columbia
foothills forests.

48. 6. Sources of Mineral Deposit. Minerals found
in the Rocky Mountains include significant
deposits of copper, gold, lead, molybdenum,
silver, tungsten, and zinc. Other areas contain
significant reserves of coal, natural gas, oil
shale, and petroleum.

49.  Minerals found in the Rocky Mountains
include significant deposits of copper,
gold, lead, molybdenum,silver, tungsten,
and zinc. The Wyoming Basin and several
smaller areas contain significant reserves
of coal, natural gas, oil shale, and petroleum.

50. Plateaus are large mountains with
large areas of flat-topped rock high
above sea level.
Most plateaus are formed when
thick, horizontal layers of rock are
slowly lifted.

51. They are found on continents around the
world, in countries ranging from Algeria to
Mexico, from Mongolia to Zimbabwe. In
Antarctica, which has a greater average
elevation than any other continent, most of
the land outside of the mountain ranges can
be considered plateaus. Covered by thick ice,
many of these areas have no names.

52. Some plateaus around the world exist at such
great heights that their climate is harsh and
living conditions are bleak. Others, at much
lower elevations, offer more favorable
conditions. The terrain of some plateaus is
unbroken and flat. The terrain of many others
has been eroded away by water and wind over
millions of years to create distinct and unusual
landforms. As such, many plateaus are
landforms filled with landforms.

54. The Shape of the Land
By definition, a plateau is a relatively level, large
expanse of land that rises some 1,500 feet (457
meters) or more above its surroundings and has at
least one steep side. A plateau may cover an area as
small as several square miles or as large as half the
size of the lower forty-eight United States. Some
plateaus formed as a result of geologic uplift, or the
slow upward movement of large parts of stable areas
of Earth's crust. Others lie between mountains,
formed in response to the collision of sections of
Earth's crust. Still others formed as a result of many
lava flows that spread out over hundreds of
thousands of square miles, building up the land
surface.

55. These latter plateaus are known as lava or basalt plateaus
(basalt is the dark, dense volcanic rock that forms these
particular lava flows). Some plateaus can form simply when
the side of a land region is weathered away
The Colorado Plateau, which spans some 130,000 square miles, is actually made up of many
plateaus . PHOTOGRAPH REPRODUCED BY PERMISSION OF THE
CORBIS CORPORATION
.
through erosion (the gradual wearing away of Earth surface
features through the action of wind and water).

56. Plateaus are widespread, covering about 45
percent of Earth's land surface. In Australia,
approximately two-thirds of the land area is
covered by the Western Plateau. This plateau
continues unbroken across much of the central
portion of the country, with only occasional
rock outcroppings. Much of the plateau has
existed as a landmass for more than 500
million years. About 25 percent of China's total
land area may be characterized as plateau. The
Tibetan Plateau in China's southwest region is
the highest and most extensive plateau in the
world.

57. As with all elevated areas, plateaus are
continuously carved by erosion, the gradual
wearing away of Earth's surfaces through the
action of wind and water. Plateaus that contain
rivers also contain canyons that have been cut
by the rivers as they have sought to reach the
level of the lake or ocean into which they flow.
Finding the path of least resistance, a river
winds across a plateau's surface, cutting
through the rock layers. Over millions of years,
a river will erode through and expose the rock
layers of a plateau, creating a canyon.

58. Plateaus may contain thousands of other landforms. Water is
the primary sculpting force for most of these. In various
forms (rain, groundwater, runoff, and rivers), water has
carved mesas, buttes, domes, towers, hoodoos, goblins,
temples, and natural rock arches and bridges across plateau
landscapes (these landforms also appear elsewhere across the
surface of Earth). In general, the relative hardness of the rock
making up a plateau determines the type of landforms
created there. If the plateau is built on sedimentary rock
(rock formed by the accumulation and compression of
sediment, which may consist of rock fragments, remains of
microscopic organisms, and minerals), its layers will tend to
be horizontal, and the landforms on it will have level or flat
tops. If the plateau is built on different types of rock of
varying hardness, its landforms may be flat or pointed.

59. Plate tectonics and plateau formation
The plates making up the lithosphere have many different
shapes and sizes. There are seven large plates, eight medium-
sized plates, and a number of smaller plates. When the plates
move, they interact with each other in one of three ways: they
converge or move toward each other, they diverge or move away
from each other, or they transform or slide past each other.
Plate margins are the boundaries or areas where the plates meet
and interact.
When two continental (land) plates converge, they crumple up
and compress, forming complex mountain ranges and very high
plateaus. This is the history of the Tibetan Plateau, created as a
result of the collision between the Indian Plate and the
Eurasian Plate. While the Himalayan Mountains formed along
the edge of the collision, the plateau rose unbroken behind
them.

60. Lava plateaus
A lava plateau (also called a basalt plateau or
flood basalt) is a special type of plateau, formed
neither by the collision of continental
plates nor by uplift. Instead, this layered
plateau is built up over millions of years by lava
repeatedly pouring forth through fissures, or
long narrow cracks in the ground. (Lava is what
magma is called once it reaches Earth's
surface.) The cracks could be where tectonic
plates are separating or where pressure from
magma underneath the crust has created cracks
in it.

61.  An area of the state of Tamil Nadu in the western portion of the Deccan Plateau.
The Deccan Plateau, which is largely made up of basalt lava, covers some
300,000 square miles in west-central India

62.  The Tibetan Plateau is the highest and most widespread plateau in the
world, with an average altitude of 16,400 feet. It also contains the two
highest peaks in the world, Mount Everest and Mount K2, and has the
deepest canyon in the world, the Yarlung Zangbo .

63. Economic Value of Plateaus
- It is an interesting place for commerse.
-The highlands are the chief seats of population; the
lowlands are the natural and the only place for the
production of most of the large and increasingly
important list of staples for which the non-tropical
regions depends upon the tropical.
-Here is a vast field for industrial readjustment by
which the people should relocate themselses where
they can have access to the best resources and those
fitted to produce the most universally desired
products.

65. Plains-type folds are local, subtle anticlines formed in
the thin sedimentary package overlying a shallow,
crystalline basement on the craton. They are small in
areal extent (usually less than 1–3 km2 [0.4–1.2 mi2]),
and their amplitude increases with depth (usually tens
of meters), which is mainly the result of differential
compaction of sediments (usually clastic units) over
tilted, rigid, basement fault blocks. The development
of these structural features by continuous but
intermittent movement of the basement fault blocks in
the late Paleozoic in the United States mid-continent is
substantiated by a record of stratigraphic and
sedimentological evidence.

66. The recurrent structural movement, which reflects
adjustment to external stresses, is expressed by the
change in thickness of stratigraphic units over the
crest of the fold compared to the flanks. By plotting
the change in thickness for different stratigraphic
units of anticlines on different fault blocks, it is
possible to determine the timing of movement of the
blocks that reflect structural adjustment. These
readjustments are confirmed by sedimentological
evidence, such as convolute, soft-sediment
deformation features and small intraformational
faults.

67. The stratigraphic interval change in thickness for
numerous structures in the Cherokee, Forest City,
and Salina basins and on the Nemaha anticline of
the mid-continent United States was determined
and compared for location and timing of the
adjustments. Most of the adjustment occurred
during and after time of deposition of the Permian–
Pennsylvanian clastic units, which, in turn, reflect
tectonic disturbance in adjacent areas, and the
largest amount of movement on the plains-type
structures occurred on those nearest and
semiparallel to major positive features, such as the
Nemaha anticline.

68. Depending on the time of origin and
development of plains-type folds, they may
control the entrapment and occurrence of oil
and gas.
Dan Merriam is a senior research scientist
(emeritus) with the Kansas Geological Survey
at the University of Kansas and a former
distinguished professor at Syracuse University
and Wichita State University. For the past
decade, he has been studying the structure
and structural development of plains-type
folds in the mid-continent and their relation to the
subsurface temperature field and occurrence of petroleum.