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World Geography
Unit 1: Land and Water Forms
The Earth’s Surface and It’s Shape
Looking at Earth from the moon what would we see?
If we could put what we see on fast forward what would we observe?
What could we explain about the earth from our observations?
The Structure of Earth
Earth is not simply a ball of rock There are distinct layers that have different
qualities. It is difficult to study the inside of the earth
because we cannot simply gaze into the earth. One method for studying the inner structure of
the planet is to study earthquakes The study of earthquakes is known as
Seismology
The Structure of Earth
The Structure of Earth
Inner Core– 2700 km in diameter– Solid– Made mostly of iron but with some nickle– Temperature of 40000C to 60000C
The Structure of Earth
Outer Core– 2300 km– Liquid, molten iron and nickel– Temperature above 40000C
The Structure of Earth
Mantle– 2900 km in thickness– Divided into two layers, upper and lower– Lower layer is mostly solid– Upper layer is called asthenosphere– The asthenosphere is in a plastic state,
sometimes solid sometimes liquid.– Made mostly of magnesium and iron silicates.
The Structure of Earth
Mohorovicic Discontinuity– The boundary between mantle and lithosphere– This is where earthquake waves abrubtly change
speed
The Structure of Earth
Lithosphere– 1-100km thick– Made up mostly of lightest elements, magnesium,
aluminum, and iron silicates such as granite– Can be divided into two layers, one under ocean
basins and one making up continents– Rocks of continents are known as the crust– Crust is 6-70km thick
Types of rock that make up the planet
Igneous: Rock that forms when molten substances cool down and harden.
Sedimentary: Rock that forms when small pieces of other rocks merge together.
Metamorphic: Rock that undergoes some physical or chemical change due to the application of heat or pressure
Forms that make up Earth’s surface
The different forms that make up the earth’s surfaces are generally known as its Topography.
Relief is the differences in elevation and slope between the higher and lower parts of the land surface of a given area.
Plains: Large flat expanses found at low elevations. Plateaus: Large flat expanses that are at higher
elevations. Mountains: Described as elevations of more that
300m; Hills would be elevations less than 300m.
A World in Constant Change
The world did not always appear as it does today
225 million years ago all of the continents were actually connected!!!
We called this super continent Pangea, and the super ocean surrounding it Panthalas
Overtime the continents eventually drifted into the positions they occupy today.
The Forces at Work
The forces that continental drift create are responsible for many of the features we see on the surface of the earth.
Mountains, volcanoes, and earthquakes are all a result of continental drift.
Plate tectonics: the movement of plates
Forces at Work
Compressional force: The force created when two plates move toward each other.– Causes rock layers to bend, warp, and move
upward.
Tensional force: Forces of tension are created where two plates are moving away from each other.– Causes large trenches where plates move appart.
Activity 1: Mapping the Plates
1. On the provided map sketch, and label a map detailing the continental plates.
2. Indicate with arrows in which direction the plate is moving.
3. Complete the chart attached to the map4. Your map should include the following map
elements.1. Legend2. North arrow3. Title
Compressional Forces
What features are created by compressional forces?– Fold mountains– Reverse Faults – Overthrust Faults
Compressional Forces: Fold Mountains
Fold mountains: Occur where compressional forces cause the land to lift upwards, creating some of the worlds most spectacular mountains.
Compressional Forces: Fold Mountains
Fold mountains take on a wave like appearance. – The peak of these waves is called the anticline– The trough of the wave is called the syncline
Anticline and Syncline Folds
Compressional Forces: Reverse Faults
Reverse Fault: When two plates push against each other one side can be pushed up over the other.
Compressional Faults: Overthrust Faults
Overthrust Faults: When folded rock gets pushed together and thrust over other layers we get an overthrust fault
Tensional Forces
What features are created by forces of tension?– Normal Faults
Tensional Forces: Normal Fault
Normal Fault: occurs when a plate on one side of a fault drops down lower than the other.
How Are Mountains Formed
Mountains are formed in three main ways– Tensional forces– Compressional forces– Volcanoes
How Do Volcanoes Build Mountains?
There are three types of volcanoes that all have distinctive characteristics– Ash-and-cinder cones– Shield cones– Composite Cones
Volcano Terms
Volcano: most common landform that is associated with extrusive volcanic activity
Vent: area of the volcano through which volcanic products erupt
Magma: Super heated melted rock below the surface Lava: Liquid rock that has reached the surface Ash: Small molten rock fragments
Volcano Forms
Ash-and-cinder cones: Typical form is symmetrical with steep sides and a large crater at the top
They form from bits of cinder and ash being ejected from the vent and building up to form a cone
These volcanoes can grow rapidly, forming mountains within a few years.
At the start
Ash-and-Cinder Volcanoes: Paricutin
Paricutin 1943
Ash-and-Cinder Volcanoes: Paricutin
Paricutin 1944
1952 - Present day
Volcano Types
Shield Cones: – Broad flat cones– Liquid lava– Mild eruptions– Little or no ash
Types of Volcanoes
Composite Volcano– Layers of ash and cinders intermixed with layers
of lava– Weak points may develop along outer walls– Periods of explosive activity, and relative quiet
Composite Cone Volcano
What Causes Volcanoes to Erupt
Heat is the major factor in Volcanic eruptions Where plates meet there is a great amount of heat When plates are pushed together one slides under
another This heat present causes rock to melt, forming
magma The pressure from the weight of the heavier rock
drives the magma up through cracks in the earths crust
Forming volcanoes.
Global Distribution of Volcanoes
Given what we know about what causes volcanoes to erupt we may say that volcanoes occur where plates meet
The most famous region of volcanoes on earth is know as the Pacific Ring of Fire
The Pacific Ring of Fire circles the Pacific Ocean.– The west coast of north and south america.– The east coast of Asia, and South toward The
southern ocean.
The Pacific Ring of Fire
