How Do Valleys Form? What Are Valleys?

in geology a valley is an extended

depression typically between hills or

mountains that is longer than it is wide

and normally has a river running through

it valleys are among the most common

features in the world and they're

typically formed through erosion which

is the gradual wearing down of material

by wind water and or other methods the

majority of valleys are either u-shaped

broad Plains or v-shaped and steep sided

or mixture of them however a valleys

form depends on many factors like what's

eroding it the slope of the land the

type of the rock and soil and the amount

of time that is vast there exist many

types of valleys however the most common

are v-shaped valleys u-shaped valleys

and flat floored valleys v-shaped

valleys are narrow with steep sloped

sides most of the time they're formed by

strong flows of water from a river or

stream which have eroded the rock under

them grinding it down to create a valley

through a process called down cutting

these rivers can often slope towards an

outlet which might be another river a

lake or an ocean these valleys often

form in mountainous or high areas with

youthful quick flowing streams that flow

rapidly a good example of this is the

Grand Canyon in the United States which

was formed by the Colorado River eroding

the rock of the Colorado Plateau over

the course of millions of years forming

its iconic shape u-shaped valleys also

known as glacial troughs have steep

sides that curve in at the base of the

valley wall and have wide floors most

are formed by massive glaciers that move

slowly down slopes eroding away the

earth these valleys are typically found

in areas high in elevation and in high

latitudes where glaciers are present

glaciers and high altitudes are called

continental glaciers or ice sheets and

while those in mountain ranges are

called alpine or mountain glaciers the

sheer size and weight of these glaciers

can completely change maps over the

course of thousands of years Yosemite

Valley in California is one of the

world's most famous u-shaped valleys it

was eroded by glaciers during the last

glaciation and now has the Merced River

running through it

flat floored valleys are the most common

in the world these like v-shaped valleys

are often formed by rivers and streams

but these streams are no longer new and

quit flowing but instead become a

meander a meander is one of a regular

series of curves bends loops turns or

windings in water course this slower

moving water tends to erode the banks of

the water channel rather than the valley

walls widening the floor of the valley

over time the shape changes from a V or

u-shape into a broad and flat valley

floor an excellent example of this type

is the Nile River Valley

there are also rift valleys that are

formed by the action of a geological

rift or Fault on the edge of tectonic

plates creating valleys like the East

African Rift at the bottom of many

valleys there's usually a base level

where the water levels smooth out due to

reaching the limits of erosion whether

by reaching sea level or erosion

resistant material this area is usually

called a floodplain

a floodplain is the area of land next to

a stream or river stretching from the

banks of the channel to the base of the

enclosing valley walls and experiences

flooding during periods of high water

discharge flood plains can support

incredibly rich ecosystems both in

quantity and in diversity they can

contain 100 or even a thousand times as

many species as rivers when they

periodically flood it releases a massive

surge in nutrients which causes

microorganisms to thrive and many other

species to take advantage of it

valleys and their associated parts

aren't just cool-looking landmarks

they've also had a great value to human

civilization from the beginning of human

society people have built near valleys

and floodplains for a number of reasons

like close proximity to rivers this is

so common there's an entire category of

River civilizations there are many

advantages to these locations like easy

access to a reliable source of water for

agriculture and human needs easy

transportation thanks to boats on the

river and very importantly the periodic

flooding of the floodplains makes for a

very nutrient-rich soil which is

excellent for farming which made it

possible to grow more crops than

necessary to sustain a population which

freed up people to engage in activities

like construction metalworking trade and

learning allowing civilizations to grow

ancient Mesopotamia was the earliest

verve Valley Civilisation forming around

3500 BC in the Tigris Euphrates River

system they were one of the first Ron's

age societies in the world developing

many technologies like metal and copper

working glass and lamp making water

storage and irrigation and many others

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