1World Geog 3200/3202Ch #1: Major Land & Water Forms

Structure of the Earth

• structure has been defined by studying earthquakes• also known as seismology

Three main parts of the Earth:

a. Crust• outermost layer• known as the lithosphere• estimated to be anywhere from 1-100 km thick• contains mountains, hills, plains, plateaus, valleys...• made of minerals and rocks

b. Mantle• middle region of the Earth• a thick layer of dense rock and metal oxides• 2900 km thick• accounts for 82% of the Earth’s volume• made mostly of perodite which is a type of rock composed

of iron, magnesium, silicon and oxygen

c. Core• centre of the Earth • anywhere from 4000-6000 degrees Celsius even though it

has been cooling for over 4.5 billion years• has two layers called the inner (solid) and outer core

(liquid) made mostly of iron and nickel

Topography:• the natural and human features of the Earth’s surface

Four common landform features of the Earth:

a. Valleys• depressions in the Earth’s crust

b. Plains• a flat region that is frequently found along the coastal areas

or at lower elevations

c. Plateaus• another type of flat region• raised upward into a higher elevation by movements of the

Earth’s crust• found in the interior of continents or between mountain

ranges

d. Mountains and Hills• highest relief landforms on Earth’s surface• hills have a height of less than 300m...usually isolated and

made up of rock piles and soil left behind by glacial erosion

• mountains have an elevation greater than 300m• occur in long linear chains on the margins of continents• rock layers are badly deformed as a result of strong forces

in and below the Earth

Importance of PLATE TECTONICS:• volcanic activity broke the Earth’s crust into tectonic plates

that carry the continents and oceans with them• tectonic plates float on a sea of hot soft rock called magma

found in the asthenosphere• the plates are constantly moving due to convection currents

which are formed when magma near the core heats then rises towards the surface as its density decreases

Compressional Forces:

• occur when tectonic plates move towards each other causing the rock layers to bend, warp and push upward

• commonly called folding

Tensional Forces:• occur when tectonic plates move away from each other,

pulling apart the Earth’s crust until it is stretched to the point where it cracks

• commonly called faulting

Anticline and Synclines• when folding occurs with the layers of the earth two simple

structures are formed:

a. Anticlines• higher areas or peaks (upfold)

b. Synclines• lower valley areas or troughs (downfold)

Compressional forces create fold mountains:• most mountains are found on the edges of continents• continental plates lie next to oceanic plates• rock layers between these two plates are squeezed upwards

making a mountain• the process of bending, buckling and pushing is called

folding• Andes Mountains were formed when the South American

plate collided with the Nazca plate • Rocky Mountains were formed when the North American

plate collided with the Pacific plate

Explain how tensional forces create a normal fault:• when plates are compressed against each other it results in

enormous pressure• the rock layers become brittle, fracture and break into a

fault• results in great blocks of the Earth’s crust being pushed up

or dropped down • if a plate on one side drops down lower than the plate on

the other side, then it results in a normal fault

Two other types of faults:

a. Reverse Fault• simple rock layers around a fault push against each other

resulting in one block being pushed up over the other

b. Overthrust Fault• when the plate that suffers the fault has already undergone

folding and its folded layers are pushed up and thrust over layers on the fault’s other side

Explain what causes a volcano to erupt:

• a volcano is triggered by heat• the plate boundaries are very hot because of friction,

pressure and decay of radioactive materials• this heat melts the rock beneath the crust making magma• magma forms in underground pockets and flows into cracks

and fractures of crustal rock• the molten rock reaches the surface through a vent• an eruption contains:a. lava - liquid rockb. ash - small molten rock fragmentsc. cinders - fine grained molten fragmentsd. gases - carbon dioxide, hydrogen, nitrogen...

• mild volcanic eruptions have thin liquidy lava with small amounts of gas

• explosive eruptions have thick lava flows with large quantities of gas, ash and cinders

Three types of volcanic cones:

a. Ash and Cinder• symmetrical shape• steep sides• large crater• results from explosive volcanic eruptions consisting of ash

and cinder with slow flowing rapidly hardening lava

b. Shield Cones• broad and flat• gently sloping sides• results from mild explosions with little ash and very thin

liquid lava

c. Composite Cones

• have an intermediate height and steepness• develops from alternate periods of violent eruptions and

relatively quiet activities• sides are made from ash, cinder and lava• weak structure that allows lava to seep through the cracks

forming smaller cones