Water Shapes the Land J. Quigley 4/2012.
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Transcript of Water Shapes the Land J. Quigley 4/2012.
Water Shapes the Land J. Quigley 4/2012 Water Shapes the Land
Water Shapes the Land The Mississippi River is like a thousand dump
trucks every year it carries more than 300 million tons of sediment
to the ocean! This sediment is being washed away from the surface
of the land and is called erosion. Water Shapes the Land The
primary force of erosion is gravity.
Gravity pulls sediment and water downhill The end result of erosion
is the deposition of sediment Deposition is the process in which
sediment is laid down in new locations Water Shapes the Land Most
sediment is moved and deposited by flowing water. Flowing water is
the major agent of erosionresponsible for shaping Earths surface
Running Water Erodes the Land
Water from rain or melted snow may soak into the ground, evaporate
or flow over the surface as runoff. Erosion begins when runoff
carries small particles of soil downhill. Runoff turns into
streams, which turn into rivers each larger body of water carries
more sediment and does more erosion and deposition Running Water
Erodes the Land
Streams and rivers erode larger particles of sediment by saltation.
Saltation is the process of particles bouncing along a stream
bottom. During floods, a fast moving river can move boulders the
size of a small car!! This breaks down the rocks into sediment.
Running Water Erodes the Land
A streams ability to erode depends mainly on its speed. Faster
streams carry more sediment than slow streams of equal size Fast
streams can also carry larger sized sediment than a slower stream
Features Formed by Water Erosion
Water erosion forms: V-shaped valleys Waterfalls Flood plains
Meanders Oxbow lakes Features Formed by Water Erosion
V-shaped valley- near a streams source, the stream flows fast as it
plunges down steep slopes. The stream erodes the rock on both sides
making the valley even steeper They often contain rapids and
waterfalls Features Formed by Water Erosion
Waterfall- A water fall develops where a stream crosses rock layers
that differ in hardness. The harder layers resist erosion, forming
the top of the waterfall. The softer rock layers are worn away,
leaving a cliff over which the waterfall tumbles. Features Formed
by Water Erosion
FLOOD PLAIN -Where a river or stream crosses gently sloping land, a
flood plain forms. As a river flows across a flood plain, it
deposits sediment The sediment builds up into long, low ridges
called natural levees These levees prevent the river from spilling
over the banks and make a channel for the river Flood plain
Features Formed by Water Erosion
MEANDERS- Where a river curves slightly, the water on the outside
of the curve moves more rapidly than water on the inside. Fast
moving water causes more erosion, there fore the river tends to
remove more soil from the outside of the curve Sediment is
deposited on the inside of the curve over time, this process forms
a loop like bend in the river called a meander. Meander Features
Formed by Water Erosion
Oxbow lake- Sometimes during a flood, a river erodes through a
narrow meander and forms a new path. Sediments build up and cut off
the old meander creating a separate, curved lake. Features Formed
by Water Deposition
As a stream or river slows down, it begins to deposit sediment.
Features deposited by flowing water include alluvial fans and
deltas. Features Formed by Water Deposition
As a stream flows out of a mountain and onto the plains, it slows
down and sediment settles out. The result is a fan-shaped deposit
of sediment on land called an alluvial fan Features Formed by Water
Deposition
When a stream flows into a lake or ocean, the water slows down. The
sediment that the stream was carrying is deposited in the form of a
delta A delta is a mass of sediment deposited where a river enters
a large body of water Groundwater Erosion The process of chemical
weathering causes much groundwater erosion, including the formation
of caves, stalactites, stalagmites and sinkholes. Groundwater
Erosion As CO2 in the air combines with rainwater it makes acid
rain. The acid rain erodes limestone making caves and caverns
Groundwater Erosion Sometimes water drips into the cavern or cave
from the rock layers above carrying minerals. Where the water drips
from the cavern ceiling, a stalactite is formed. Groundwater
Erosion If the water drips down to the floor, a pillar of minerals
called a stalagmite is formed. Groundwater Erosion If erosion
weakens a layer of limestone, entire portions of the ground can
suddenly collapse resulting in a sinkhole. Glaciers and Wind
Glaciers form in places where more snow falls than melts or
sublimates. As the layers of snow pile up, the weight on the
underlying snow increases, eventually turning the snow into ice or
a glacier Glaciers Even though glaciers appear to be stationary,
they are actually moving! The force of gravity pulls the ice down
hill, the ice flows very slowly. Glaciers There are two types of
glaciers: Continental glaciers
Valley glaciers Glaciers Continental Glacier- thick sheet of ice
that covers a huge area, such as a continent or large island. Most
of earths fresh water is frozen in the continental glaciers that
cover Antarctica and Greenland Glaciers Valley Glacier- Occur high
in a high mountain valley
A valley glacier usually begins near a mountain peak and winds down
through a valley formed originally by a stream Glacial Erosion and
Deposition
Glaciers are very effective at eroding rock. Glaciers erode rock
through abrasion and plucking. Plucking is when glacier ice widens
cracks in bedrock beneath the glacier, and those pieces are frozen
and stuck to the glacier. As the glacier moves, the rocks get
plucked out of the ground and pulled down with the glacier Features
formed by glacial erosion
Glaciers cause many distinctive features in the landscape,
including: Cirques Horns U-shaped valleys Glacial lakes Features
formed by glacial erosion
Cirque- a large bowl shaped valley in the mountain side caused by a
glacier. They look like they were made with a giant ice cream
scoop. Features formed by glacial erosion
Horns- If several cirques form close together, a ridge my be left
between them, if several ridges connect to form a pyramid-shaped
peak. The sharp peak is called a horn. The peaks of the Swiss Alps
were made by glaciers Features formed by glacial erosion
U-Shaped Valley- Glaciers widen and deepen existing valleys. When a
glacier flows through a V-shaped valley it carves out the rocks
through plucking and abrasion, making it a U shape instead Features
formed by glacial erosion
Glacial lake- Continental glaciers can enlarge and deepen natural
depressions in the ground. These depressions then fill with water
when the glaciers retreat. The Great Lakes in the USA are glacial
lakes. Features formed by glacial deposition
A glacier gathers and transports a huge amount of rock and soil as
it moves. When a glacier melts, it deposits its load of sediment,
creating a variety of landforms. Features formed by glacial
deposition
Glacial sediment is called till. Till is an unsorted mixture of
sediment containing fragments of many sizes. Giant boulders,
gravel, sand and rock dust are all found in till Glaciers deposit
till as they melt Features formed by glacial deposition
Moraines form from till. A moraine is a mound of sediment at the
downhill end of a glacier and along its sides. Wind Erosion and
Deposition
Wind can also cause erosion and deposition The speed of the wind
determines the size of the materials it carries. Slow wind carry
only small particles, while fast winds can move large boulders!
Wind Erosion and Deposition
Wind erodes the land by deflation and abrasion. Deflation occurs
when wind picks up and carries away loose surface materials. Wind
Erosion and Deposition
Dry regions where winds are strong, sand and dust are lifted from
the surface and carried away. Over time, the surface of the ground
is lowered, larger rocks are left behind, forming a rocky surface
that covers much of the land in dry regions Wind Erosion and
Deposition
Abrasion is a form of mechanical weathering. Abrasion by wind
occurs in much the same way as abrasion in flowing water. Wind
blows sand against other rocks slowly sandblasting them away and
removing the weathered particles Effects of Wind Deposition
When wind slows down it drops the sediment it is carrying. Features
deposited by wind include sand dunes and loess deposits Wind
Erosion and Deposition
Deposits formed from windblown sand are called dunes. Wind Erosion
and Deposition
Deposits formed from windblown dust are called loess. Loess
consists mainly of finely ground particles. The Restless Ocean
Oceans surround all of the continents
Earths ocean waters are divided into four major oceans: The Pacific
Atlantic Indian Arctic These oceans also include smaller bodies of
water such as seas and gulfs. Exploring the Ocean Exploring the
Ocean Most of Earths water is exists as salt water in the oceans.
Ocean water is a mixture that includes dissolved salts and gases
Salinity is the proportion of dissolved salts in water. On average
there are about 35 grams of dissolved salts in each kilogram of
ocean water. Exploring the Ocean Salt is added to the oceans by
rivers and volcanoes. Rain slowly dissolves salts out of surface
rocks All the salts get deposited in the oceans, making them salt
water Changes with Depth Conditions in the ocean, such as the
amount of sunlight, temperature and pressure change as you move
from the surface to the ocean floor. Light and temperature decrease
with depth, and pressure increases Exploring the Ocean Sunlight
decreases with depth. The deep ocean is totally dark Light cannot
penetrate deeper than 200 meters Exploring the Ocean Water
temperature decreases with depth.
The top 100 to 500 meters of the ocean are well mixed and
relatively warm. Deeper water is much colder and denser. Deep water
moves very slowly and does not interact much with the surface layer
Exploring the Ocean Pressure increases continuously with depth in
the ocean. At a depth of 500 meters, the pressure is about 50 times
greater than the atmospheric pressure at sea level. Few forms of
life can tolerate such great pressures Exploring the ocean At the
coast line, there are reefs and shallow waters called the
continental shelf At the edge of the continental shelf, the
continental slope descends steeply to the floor of the deep ocean
Exploring the Ocean The ocean floor- is a vast, flat plain dotted
with volcanic peaks. It also contains the mid ocean ridges. There
are also basins and trenches along the edges of some oceanic plates
Exploring the Ocean Mariana Trench is the deepest place on earth,
11 kilometers below sea level!!! Overall, the average depth of the
ocean is about 3.8 meters to the floor! Ocean Currents Currents are
the patterns of the oceans.
Ocean Currents are affected by winds, earths rotation and the
position and shapes of the continents. Ocean Currents Surface
currents- A surface current is a large stream of ocean water that
moves continuously in about the same path Winds blowing across the
surface of the ocean cause the continuous flows of surface currents
Ocean Currents Unlike surface currents, deep currents are not
caused by winds Deep ocean currents are caused by differences in
the density of the ocean water Denser water results from colder
temperature or high salinity Because deep ocean currents are
affected by density, they are called density currents Ocean
Currents Density currents are responsible for a slow mixing of the
water between the surface and deeper ocean. Ocean Currents In
certain places in the oceans, water from the deep oceans moves
upward toward the surface. The movement of water from the deep
ocean to the surface is called upwelling. Ocean Currents In
upwelling, winds blow warm surface water aside, this allows cold
water from the deep ocean to rise and take the place of the warmer
water. This is important for mixing oxygen and nutrients in the
ocean Wave Erosion and Deposition
Two physical processes, hydraulic action and abrasion are
responsible for wave erosion Over time, wave erosion and deposition
work together to straighten a coast line Wave Erosion In the
process of hydraulic action occurs when waves pound on cracks in
rocks. As water forces its way into the cracks, rocks break off.
The rock pieces are then turned to sediment through abrasion Wave
Erosion Sand is continuously eroded and deposited along the shore
by waves and currents Longshore drift is the process that moves
sand along the shore. As waves break, they carry sand up the beach
at an angle. This angled sand is longshore drift. Deposition by
currents and waves
Sediments in the ocean are eventually pushed up on land and create
beaches