RELIEF


1.- WHAT IS THE EARTH MADE OF?


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The interior of the Earth is divided into concentrical layers.
  • CRUST: It is a thin outer layer formed by solid rocks. It is divided into continental and oceanic.
  • MANTLE: It is the middle layer, formed by solid rock or half-molten. It is divided into upper and lower.
  • CORE: It is the deepest layer. It is composed of iron and nickel. Its temperature is very high (4.300º C). It is divided into internal and external.
    The most interesting part of the Earth structure is the Lithosphere.







2.-WHAT IS THE EARTH´S RELIEF?


The Earth´s relief is the form that the surface of the earth's crust (Lithosphere) has. It includes the emerged and submerged land under the floor of the oceans and seas.
Water covers about 71% of the Earth's surface. Of this amount, 97% is salt water.
Salt water is located in oceans and seas. Fresh water is located in rivers, lakes, glaciers and groundwater.

Earth's water is contnuosly changing its physical state (liquid, solid or vapor) and moves from one to another place.
This process is called as water cycle (or hydrologic cycle) and involves evaporation, condensation andrainfall.


Continental relief

The continents occupy approximately 30% of the earth's crust. They comprise the emerged land and the nearby submerged area, called continental shelf.

There are six continents: img2.gif, Asia, America, Africa, Antarctica, Europe and Oceania.
Most of the emerged land is in the northern hemisphere.

Continental forms
The main continental relief forms are:


  • MOUNTAINS: They are natural elevations of the land with pronounced sides.
  • VALLEYS: They are sunken areas that are surrounded by high land, such as mountains. They are usually crossed by rivers.
  • PLAINS: A plain is a large geographic area slightly above sea level.They are usually made up of materials from erosion, known as sediments.:
  • PLATEAUS: They are elevated regions above their surroundings.The highest plateaus are located in Tibet (Asia) and in Bolivia (South America). They are formed by ancient eroded mountains.
  • BASIN: It is a natural depression made up from the accumulation of sediments, produced by the erosion of the Earth's surface, for example, by a river.
Some of them are below sea level.

Coastal relief


The sea produces different forms in the relief of coastal areas:
  • BEACH: It is a geographical area that consists in the accumulation of unconsolidated sediments by the effect of the local movements of the waves. These sediments are typically sand, but there are also beaches formed by gravel and rocks.
  • CLIFF: It Is a significant vertical and steepy rock formation in the coast. Cliffs are made by erosion.
  • PENINSULA: It Is a piece of land surrounded by sea water on all its sides except on one, slightly narrow, called isthmus.
  • CAPE: It is a part of the coast which extends into the sea. It can have a great influence on ocean currents and navigation.
  • GULFS: They are parts of the ocean or sea that are partly surrounded by land. If the gulf is small, it is called Bay.
  • ISLAND: It Is a piece of land smaller than a continent, which is completely surrounded by water. A group of islands is called an archipelago.

Oceanic relief


It has to do with the oceans and seas. It is varied and irregular.
It includes:
  • Continental shelf
It is the submerged margin of the continents, extending from the shore to the first prominent break in the slope, which usually occurs at a depth of about 120-200 m. It is near the coastline.
  • Continental slope
The slope that extends from the continental shelf down to the ocean depth.
  • Abyssal plain
It is the deepest part of the seafloor, below 2.000 metres.
  • Oceans trenches
Deep-sea trenches are the deepest parts of the ocean. The deepest one, the Marianas Trench in the South Pacific Ocean, is 10,668 meters deep.
  • Oceans ridges
Large mountains located in the oceans floor. Rise up as far as 3000 m. Some of them protrude from the surface and form islands.



3.-WHY DO LANDSCAPES CHANGE?

Erosion
  • What is erosion?


Erosion is the action of wind, water and ice that dislodges, dissolves or removes surface material.(1) When material is removed from one location, it is inevitably placed somewhere else; this is called deposition. Both erosion and deposition are natural processes. But when human activities substantially alter, increase or impede the natural movement of sediment, serious damage can occur.

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  • How does erosion occur?


Over time, even the largest mountains are worn down by weathering and erosion. Weathering is “rock decay,” which occurs through physical, chemical and biological processes. Once the minerals have been weathered and broken down, they are prone to being transported (eroded) by wind, water and ice.

The impact of raindrops on bare ground dislodges soil particles and causes erosion on the smallest scale, termed rainsplash erosion. When water flows across sloped surfaces, it tends to form rivulets; these can create small channels in soft soil or sediment, and cause rill erosion. With enough rainfall on exposed earth, rivulets join together and gouge gullies in the land. Such processes can transport large amounts of topsoil and sediment from the land into water bodies.

In some places, such as prairies, deserts and coastal sand dune systems, wind causes erosion. The infamous “Dust Bowl” of the prairie states and provinces in the 1930s was caused by wind-driven erosion of soil that had been damaged by drought and intense farming practices.

As explained in coastal sediment processes, shoreline erosion is a natural phenomenon. Bluffs are continually worn away by the action of waves and rainwater, and their sediment nourishes sandy beaches. Sand and cobble beaches themselves are part of a constant cycle. Winter storms wash away the fine material, and smaller summer waves gently replace it.

Erosion caused by rivers and streams is also basically a natural process. Especially during times of high rainfall, streams can move large amounts of sediment.


Sediment removed by erosion is deposited when the flow of wind or water slows down. For example, when a stream or river widens, the water slows and sediment that was carried along drops to the bottom. In this way, a delta is formed at a river mouth in a sea or lake.

  • How do human activities contribute to erosion?


Soils in this part of the world are usually covered in thick vegetation. Herbs, grasses, shrubs and trees help to prevent excessive erosion caused by heavy rains in a number of ways:


* Leaves and stems intercept the direct impact of raindrops, helping to prevent rainsplash erosion;


* Roots create channels for rainwater to soak into the ground, help to anchor soils, and protect stream banks from the force of rushing water;


* Decaying plant matter accumulates in and on top of the soil, creating a spongy “mat” that soaks up rain and prevents the soil from being washed away.

When vegetation is removed, these natural functions are lost. Agriculture, logging, construction and road building usually involve removing existing vegetation. Unless these activities are carefully planned to minimize damage, erosion often occurs.


When human-made structures stand in the way of coastal sediment processes, problems arise. One worst-case scenario is a slope failure that damages or destroys a house built too close to the shoreline. Compaction of the soil, from the weight of structures, and excessive irrigation contribute to this situation. Vegetation removal, infilling, shoreline armouring, and construction of seawalls and groynes are practices that can cause shoreline erosion (see altered shorelines).


Human activities substantially affect on the energy of a stream. Impervious surfaces such as roads and parking lots cause unnaturally large volumes of rainwater to flow into streams, increasing the stream’s destructive power. Erosion can scour away the land beside a stream, and deposit large amounts of sediment downstream, in areas of slower stream flow.

  • How does erosion affect ecosystems?


Topsoil is formed over hundreds to thousands of years, through complex interactions among the bacteria, fungi, worms and insects, that live among the roots of plants and help to break down organic matter. When topsoil is washed away by erosion, the land becomes much less fertile, and can support fewer plant and animal species.


Soil and sediment that is washed into natural water bodies degrades water quality and fish habitat in a number of ways:


* Light penetration of the water is decreased in murky water, impeding the growth of aquatic plants;


* Gravel spawning beds used by fish such as salmon and Cutthroat Trout can be buried and smothered;


* Fish gills become clogged, and sediment irritates the mucous membranes of the skin and eyes, making fish more susceptible to disease and infection.

Excessively high water flows associated with impervious surfaces and vegetation removal can destroy and degrade habitat for a wide range of plants and animals. This occurs when land adjacent to the stream is destroyed, or characteristics of the stream bed are altered, either by excessive erosion or deposition. The effects of habitat loss for even a few species are felt throughout the food web, since biodiversity is lost and ecosystems cannot function properly.

Paradoxically, a lack of sediment can cause damage to ecosystems as easily as excessive sediment. Some types of shoreline rely on the deposition of sediment supplied by natural erosion to retain their habitat characteristics. For example estuaries, deltas, salt marshes, coastal sand dunes and sand and gravel shorelines all require regular, natural deposition of various types of sediment. Fine sediment such as sand and silt provides the primary material in which plants root and certain animals burrow. Human-made structures such as seawalls and groynes prevent sediment transportation, and starve nearby shores of fine sediment (see coastal sediment processes). This results in a gradual coarsening of beaches, and habitat loss for burrowing invertebrates living in the sand, and loss of a food source for the birds that feed upon them.

Dams also prevent the downstream movement of sediment, since it falls out of the water in the calm reservoir behind the dam. Areas such as floodplains and estuaries are then deprived of the gravel and sediment necessary for their proper function. For example, salmon require gravel beds for spawning, and fine sediment accumulates among tree root masses and log jams, creating new soil for riparian plants to grow in.

Erosion damage can create a window of opportunity for invasive species. Native species often cannot cope with the changes in soil characteristics and water quality. In contrast, certain invasive species may have evolved tolerances to these conditions, since they come from a different landscape. One example is Scotch Broom, which is able to grow in very nutrient-poor soils.

  • How does erosion affect people?


  • When erosion occurs on a large scale such as a landslide, it can result in devastation of communities, roads, land and even lead to loss of life.
  • Loss of topsoil can render the soil much less fertile for farming. Three quarters of the cultivated land in B.C. is considered to have a high to severe risk of erosion by water; 36 percent of farmland in the Prairies is at a high to severe risk of wind erosion.
  • Habitat loss can negatively affect commercially important species such as salmon.
  • Excess sediment in drinking water can increase the cost and reduce the effectiveness of water treatment.
  • Coarsening and steepening of beaches, caused by shoreline erosion, makes them less attractive for recreation.
  • The effects of erosion degrade the landscape, making it less attractive from a recreational and aesthetic point of view; this can also affect the tourism economy.
  • Erosion damage to valuable ecosystems such as wetlands and estuaries reduces their ability to provide important services such as flood control, water storage and filtration, and protection from storm waves.






Sedimentation


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Sedimentation in the geological sciences, process of deposition of a solid material from a state of suspension or solution in a fluid (usually air or water). Broadly defined it also includes deposits from glacial ice and those materials collected under the impetus of gravity alone, as in talus deposits, or accumulations of rock debris at the base of cliffs. The term is commonly used as a synonym for sedimentary petrology and sedimentology.
The physics of the most common sedimentation process, the settling of solid particles from fluids, has long been known. The settling velocity equation formulated in 1851 by G.G. Stokes ..



4.-WHAT ARE VOLCANOES AND EARTHQUAKES?

A volcano is a fissure in the earth's crust through which molten lava and gases erupt.mantle-convection.gif
The leaving of the lava may be joined by explosions that eject fragments of rocks, slags and ashes.
Often the volcanoes are located on the boundaries of tectonic plates.








A geyser is a natural hot spring that periodically vaporize a fountain of water and steam into the air.
Geysers can be founded in the same areas as volcanoes.

A volcano has differents parts:


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  • CRATER: It's the top. Through him go abroad eruptive materials.
  • CONE: It's where the materials accumulated are expelled. When the volcanoes are found in marine waters, can form islands.
  • PIPE: It is the tube that connects the interior and exterior of the volcano
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An earthquake is a shaking or vibration at the surface of the earth resulting from underground movement along a fault plane of from volcanic activity.
Earthquakes are caused by movement of the tectonics plates. When two plates crash, release a large amount of energy, causing tremors that could be very violent.

Earthquakes can produce on the ocean floor. Then they are called "tsunamis".

PARTS OF AN EARTHQUAKE

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1.-HYPOCENTRE or HIPOCENTER . Literally: "'below the center", from the Greek υπόκεντρον.
It is the place inside the Earth where an earthquake originates, causing the seismic waves.

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2.-SEISMIC WAVES. They are waves that travel through the Earth. They can pass through the earth like water.
3.- EPICENTRE or EPICENTER . From the Greek επίκεντρον.It is the point on the Earth's surface that is directly above the hypocenter.
The force of an earthquake can be measured by seismographs.

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SEISMOGRAPHY is the measurement and recording of the vibrations of earthquakes with a seismograph.

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Seismometers or seismographs:They are the device used by experts to measure and record the size and force of seismic waves.
By studying seismic waves, seismologists can measure and locate earthquakes.
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5.- EXERCISES