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 erosion responsible for shaping Earth’s 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 stream’s 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 stream’s 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 earth’s 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 Earth’s 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 Earth’s 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, earth’s 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