Download Foundations of Social Studies GEOGRAPHY

Foundations of Social Studies
GEOGRAPHY
LANDFORMS
A landform is any natural formation of rock or dirt. Landforms can be as large as a mountain range,
or as small as a hill; as “uninteresting” as a plain, or as fascinating as an arch. Geographers and
geologists study how landforms are created, how they evolve and change, and where they are
located.
A term which is synonymous with the term landforms is topography. For example, we might say
that the topography of an area is rough, if it is mountainous or hilly. We might say the topography is
smooth, if it is a plain or if we are talking about a valley which has been carved by a glacier. The
walls of many canyons have steep topography. If we are talking about a very large area, we would
not be surprised if it was described as having varied topography because it had a wide variety of
landforms.
Below is a list of some important basic types of landforms but there are many, many more.
arch
butte
dune
mountain
sinkhole
archipelago
canyon
gulf
peninsula
strait
atoll
cape
isthmus
plain
valley
basin
cliff
mesa
plateau
volcano
bay
delta
moraine
promontory
The Creation of Landforms
The great variety of landforms on earth are the result of two basic forces: internal forces –
which are those that come from deep inside the earth and push the landforms up, and external
forces – which are those present on the surface of the earth or in the earth’s atmosphere and
which wear the landforms down.
Internal Processes
The internal forces are usually called tectonic processes. The surface, or crust, of the earth
is made of about a dozen rigid slabs, called plates. These are much larger than the
continents as huge portions of the plates are under the oceans but still part of the same
plate as the neighboring continent. Through a process called plate tectonics, these giants
slabs move slowly across the surface of earth. As they do so, they grind past each other,
push on top of each other and, in some places, are torn apart. As the plates move, grind,
split, crash, and crumple they create some of the world’s largest landforms – mountain
chain, plateau lands, and islands – by pushing each other up. When it occurs it feels jarring
to humans and are called earthquakes, these changes in the plates happen very slowly,
taking millions of years.
How are these giant tectonic plates able to move slowly across the earth? Underneath the
rigid layer of crust on which we live are deeper layers which are not solid. The earth’s
crustal plates are able to move slowly across these inner layers which consist of molten rock
called magma. Sometimes this magma is able to force its way up to the surface and form a
volcano. This is especially common along the edges of some of the plates. Volcanism is
another internal process which shapes the landforms we see on the surface of the earth.
External Processes
The surface of the earth is subject to forces which change its shape. The most important
forces are weathering and erosion. Weathering occurs when rock surfaces decompose and
begin to break up. Erosion refers to the actual movement of the broken particles away from
their source. These two processes occur at the same time and result in the changing shape
of land, that is, the creation of landforms.
Weathering is caused by water on the surface of rocks, by plants whose roots break up
rocks, and even by animals. There are also many ways for erosion to take place once
weathering has begun to break a rock down. Rainfall, rivers, and glaciers, can all move those
portions of rock which have been weathered and carve the surface of the earth. Coastlines
– along lakes, seas, and oceans – are subject to erosion by the pounding of waves. Wind is
another important erosional force.
Different types of rocks result in different types of landforms. This is because different minerals,
of which the rocks are made, erode in different ways. For example, if the surface area of a
region is made of limestone it is likely that there will be many caves because limestone erodes
easily in water. If a region is made of sandstone - large dunes, gravel deposits and steep cliffs
may be expected.
Man can also effect the creation of landforms. As pollution and chemicals in the air mixes with
precipitation, the result is acid rain which can erode minerals more effectively and kill plant life.
The loss of plant life leads to increased erosion. Overgrazing of animals and deforestation can
also lead to increased erosion. Finally, man has the technological and mechanical ability – with
the use of machinery – to physically alter the landforms of the earth by digging, blasting, and
moving huge portions of the surface.
Physiographic Regions
Geographers divide the surface of the earth into huge regions based on the predominant type
of landform found in the region. These are called physiographic regions because they are based
on physical features. They are also sometimes called landform regions. The United States is
usually divided into 25 separate and distinct regions based on physical geography. The largest
region in the eastern US is the Coastal Plain. Two large regions make up most of the central
United States. They are the Central Lowland and the Great Plains. In the western United States
the largest single region is the Great Basin, but the Rocky Mountains cover nearly as large a
territory.
In summary, the earth’s surface can be divided into regions based on the topography, or
landforms, which are found there. The topography is created by internal forces which push the
land up and by external forces which wear it down into different shapes. These shapes, called
landforms, are based on the type of rock of which they are made and the type of erosion which
is wearing it down. Regions based on physical features are sometimes called physiographic
regions.