OUR CHANGING EARTH
THE LITHOSPHERIC PLATES
The outer layer of the Earth is called the lithosphere. It is broken into several big pieces, called lithospheric plates.
These plates move slowly, only a few millimetres each year. This happens because hot molten magma (liquid rock) inside the Earth moves in a circular way.
This movement causes changes on the Earth's surface.
EARTH MOVEMENTS
There are two types of forces that cause movements on Earth:
Endogenic forces – come from inside the Earth.
Exogenic forces – act on the surface of the Earth.
ENDOGENIC FORCES can be:
l Sudden, like earthquakes and volcanoes.
l Slow, like the formation of mountains.
VOLCANO
l A volcano is an opening in the Earth's surface where molten material (lava) comes out suddenly.
EARTHQUAKE
1. An earthquake happens when the plates move and cause shaking on the Earth.
2. The place inside the Earth where the earthquake starts is called the focus.
3. The place on the surface above the focus is the epicentre.
4. The shaking is strongest near the epicentre.
5. Earthquakes cannot be predicted, but we can reduce damage by being prepared.
6. People sometimes watch animals to guess when an earthquake might happen.
For example:
l Fish become restless
l Snakes come out of the ground
MAJOR LANDFORMS
l The Earth's surface is always changing because of weathering and erosion.
l Weathering: Breaking of rocks on the surface.
l Erosion: Wearing away of land by water, wind, or ice.
l The broken material is moved and then deposited elsewhere.
l This creates different landforms like mountains, valleys, and plains.
WORK OF A RIVER
l Rivers wear away land.
l When water falls from a height, it creates a waterfall.
l On flat land, rivers form meanders (big curves).
l When a meander gets cut off, it forms an ox-bow lake.
l During floods, rivers deposit sediments, creating floodplains (flat fertile land) and levees (raised banks).
l Near the sea, rivers slow down and split into small streams called distributaries.
l These form a delta (a triangle-shaped land made of deposits).
WORK OF SEA WAVES
l Sea waves break rocks on the shore.
l This creates sea caves, and later sea arches.
l When the arch breaks, only the wall is left, called a stack.
l Steep coasts are called sea cliffs.
l Waves also form beaches by depositing sand.
WORK OF ICE (GLACIERS)
l Glaciers are like rivers of ice.
l They move slowly and carry rocks, soil, and sand.
l They carve deep holes which later fill with water to become lakes.
l The deposited material is called moraines.
WORK OF WIND
l Wind is active in deserts.
l It forms mushroom rocks by eroding the bottom more than the top.
l Wind moves sand and forms small hills called sand dunes.
Very fine sand can travel far and form loess (soft soil), like in China.
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