MOUNTAIN RANGE FORMATION
By Pilar Baumann
Mr. Martinez , Instructor
East Whittier Middle School
Mountains are grouped into four types: volcanoes,
fault-block mountains, complex or folded mountains and erosional
mountains. They are categorized into different groups according to the way
they are formed. Thus, all mountains are not formed the same way.
The first type is volcanoes which are made when solid rock and
liquid lava erupt from the inside of the earth. Magma is liquefied rock .
When magma is blown or flows out of the volcano it is called lava. When a
volcano ejects ash and cinders during an eruption this is called
Pyroclastics . Volcanoes are many different sizes . They also fall into
two basic types: Cinder cones, like Mount Vesuvius in Italy are
characterized by explosive eruptions and a rhyolitic lava.1
The other kind is shield volcano like Mauna Loa, in Hawaii
which is characterized by a flattened dome that originates from flows of
fluid basaltic lava.2 Some volcanoes
grow very fast. In 1943 in Mexico a farmer spotted a small pile of ash in
the middle of his field. He thought no more of it. In a couple of hours it
was taller then he was. In six days it was nearly 500 feet. Today the pile
is called Mount Paricutin and is almost 9,000 feet.
Mt. Saint Helens
The second group is fault-block mountains which are formed by
the movement of large cluster blocks along faults formed when tensional
forces pulled apart the crust.3 A
fault is a line along where two tectonic plates4
or bits of plates come together or one is sliding on top of the other.
Faults sometimes slip or move suddenly because of the movement of the
crust, causing earthquakes. After a very big earthquake, the ground on
either side of the fault sometimes doesn't fit together as well as it did.
Sometimes the ground on one side of a fault is left higher then the other
side. The side of the ground that is left higher or any peak on it forms
what is called a fault-block, or mountain range.
The third category is folded mountains or complex mountains which are made when two tectonic plates start to push against each other. Earths crust gets pushed up and often creases up. Folded mountains take very long to form because tectonic plates only move a few centimeters a year. Millions of years ago tectonic plates crashed together and made up most of Asia . This caused the Himalaya mountain range to rise. The Himalayas now make the boundaries between Asia and the Indian sub-continent. The Himalayas are the biggest mountain in the world . The Himalayas highest point reaches 30,000 feet above sea level.
The last kind is erosional mountains which are formed when wind
and rain wear away part of a landscape . For instant a volcano is made up
of soft rock on the outside and very hard solid lava on the inside. So
when the soft rock is worn away by the weather the hard rock remains.
Erosion mountains look tall and thin like cylinders coming out of the
earth. Sometimes water and ice cuts through a rock leaving the high part
alone. The peak that remains is called an erosional mountain.
In conclusion, we have seen that there are four different types of
mountains: volcanic, which are divided into two sub-categories:
cinder cone and shield volcano; fault-block mountains, complex
or folded mountains and erosional mountains. Weve
also seen that mountain types are categorized by the way they are formed,
each group different from each other.
Deborah K. Smith, Susan E. Viewing the morphology of the
Ridge from a New perspective.
Grolier Multimedia Encyclopedia. 1997. Mindscape, Inc. mountains
Hot News. "Introduction to Mountains 1998. <http://www.eduweb.co.uk/news/mount/mrintro.html>
WVGES. Feature Article - Mountains 1998. <http://www.wvgs.wvnet.edu/www/geology/geolf001.htm>
Stokes, William and Judson, Sheldon. Introduction to Geology. New Jersey: Prentice Hall, 1968.
Fault Block Mountain
1 Rhyolitic lava is a lava that comes from rhyolite, an igneous rock that is fine grained and rich in silica.
2 Basaltic lava is lava that comes from basalt, a dark dense igneous rock made up of labradorite and pyroxene and many times displays a columnar structure.
3 The crust is the top layer of the earth.
4 Tectonic Plates are plates that are on top of the mantel and under the crust of the earth.