.jpg)
Mostrando entradas con la etiqueta colegaio campestre colombo britanico zipaquira. Mostrar todas las entradas
Mostrando entradas con la etiqueta colegaio campestre colombo britanico zipaquira. Mostrar todas las entradas
jueves, 20 de agosto de 2009
.jpg)
The external forces of earth.
Wind, water and people erode the relief of earth surface.
These changes occur slowly, over millions of years.
External changes happen in three phases:
1. Erosion: is the constant wearing away of rocks and soil.
Temperature, water, wind and people cause erosion.
· Sharp changes in the temperature: break rocks into fragments. This occurs in areas where there is a big difference between daytime and nighttime temperatures, such as mountains and deserts. Sometimes water that has filtered through cracks in rocks freezes. This act like a wedge and breaks the rock.
· Rainwater, rivers and oceans: constantly erode the ground.
Rain and snow dissolve the materials in the soil. Rivers wear away banks and erode materials from the rivers bed.
They create deep valleys and canyons. The waves of the ocean wear away the coasts. Underground water hollows out large caves.
· The wind: mostly erodes soft rocks. It also erodes places where there is a lot of sand, like deserts and beaches.
· The people: cut down forests. They cause fires, build slopes, etc. this actions cause erosion of the soil.
2. Transporting materials: eroded materials are transported from one place to another. The wind, river currents and ocean water transport these materials. Wind curries sand and small rocks. Rivers and oceans carry large amounts of dissolved materials. They also carry larger materials floating on the surface.
3. Sedimentation: occurs when the materials carried by water, ice or wind are deposited. The accumulation of these materials leads to changes in the lanscape.
· A river transports the materials. It deposits them on its banks to create terraces. It deposits at is mouth to create deltas.
· Ocean waves deposit materials on the low shores. The deposited materials create beaches.
· The wind transports large quantities of sand. This creates dunes in deserts and on the coast
}
The internal forces of Earth
Earth changes: the relief of earth’s surface has not always been the same.
For example:
Islands and mountains have formed throughout time. Millions of years ago, there were plains where today there are mountains, and vice versa. Land now on the surface used to be under the ocean.
These changes occur as a result of the internal and external forces of earth.
Internal forces: create the surface relief.
External forces: erode the surface little by little.
Earthquakes: occur when internal forces break or move rocks inside earth. The rocks knock against each other and cause very intense and destructive seismic waves.
Earthquakes begin inside earth at a point called focus.
This point is called the epicenter on the surface.
The size or force of an earthquake is measured by a sale called richer scale and goes from 1 to about 9. The most intense earthquakes can change the lanscape.
Volcanic eruptions:
There are very hot substances inside earth. Sometimes these substances break through to the surface. They come out through to the surface. They come out through volcanoes.
The hot materials form magma. Internal forces put pressure on the magna and it rises through the central vert and comes out of the crater.
The substances that the volcano expels can be solid, like ash. They can also be liquid like lava. Volcanoes can also expel gases, which can cause explosions inside the volcano.
These expelled substances build up on the outside of the volcano and form volcanic cones. Sometimes volcanic eruptions can even create islands, such as the Hawaiian Islands.