Internal Forces Shaping the Earth
Chapter 2,Section 3
Plate Tectonics
Tectonic Plates aremassive, moving piecesof Earth’s lithosphere
Plates ride abovecirculating, heatedrock
Geographers studyplate movements tounderstand:
How the earth isreshaped
How earthquakes andvolcanoes are formed
Pate Tectonics
Plate Movement
Plates move in one of four ways:
By spreading, or moving apartDIVERGENT
Subduction, or diving under anotherplate CONVERGENT
Collision, or crashing togetherCONVERGENT
Sliding past each other in a shearingmotion TRANSFORM
PLATE TECTONICS
Divergent Boundary – platesmove apart, spreadinghorizontally
Example: Saudi Arabia-Egypt’s plates are spreadingapart, widening the Red Sea
PLATE TECTONICS
Convergent: Subduction – Asplates are pushed together,one plate is forced under theother in a process calledsubduction. (Volcanoesformed at surface)
Convergent: Collision – When2 continental plates collide,neither one is subducted,and the plates buckle andfold. (Mountains are formed)
PLATE TECTONICS
TRANSFORM BOUNDARY– Plates slide past eachother along a fault orfracture in the crust.(Does not create newlandforms, causesEARTHQUAKES)
Example: San AndreasFault in California
Plate Tectonics
Folds and Faults
2 plates meeting can cause folding, cracking ofrock
Fault – occurs when pressure causes rock tofracture, or crack
Fault Line is place where plates move past eachother
Earthquakes
THE EARTH TREMBLES
An earthquake occurs when plates grind or slip ata fault line
A seismograph detects earthquakes and measuresthe waves they create
EARTHQUAKE LOCATIONS
Location in the earth where an earthquake beginsis called the focus
Epicenter – the point directly above focus on theearth’s surface
Nearly 95% of earthquakes occur at tectonic plateboundaries
EARTHQUAKES
EARTHQUAKE DAMAGE
Earthquakes release energy in the form ofmotion, causing:
Landslides
Land displacement
Fires (broken gas lines)
Collapsed buildings
Richter Scale – numeric scale showing relativestrength of earthquake
Earthquakes
Tsunami
Tsunami – a giant ocean wave, begins atepicenter of an earthquake:
Travels up to 450 mph
Waves of 50-100 ft. or higher
Volcanoes
The Explosive Earth
Volcano – underground materials pour from crackin the earth’s surface
Most volcanoes occur at tectonic plateboundaries
Volcanic Action
Eruption – lava, gases, ash, dust, explode form ventin Earth’s crust
Lava – magma that has reached the earth’ssurface; may create landform
Volcanoes
Ring of Fire
Ring of Fire – zone around thePacific Ocean
Meeting point of 8 tectonicplates
Vast majority of the earth’sactive volcanoes locatedhere
“Hot Spots” are wheremagma rises to surface frommantle
Hot springs, geysers indicatehigh temperatures in earth’scrust
Some volcanic action isuseful:volcanic ashproduces fertile soil
Hot springs are tapped forheat, energy
Chapter 2, Section 4External Forces Shaping theEarth
Weathering
Altering the Landscape
Weathering – processes that alter rock on or nearthe earth’s surface
Can change landscapes over time and create soilfor plant life
Sediment – mud, sand, silt created by weatheringprocesses
Mechanical Weathering
Mechanical weathering – processes that breakrock into smaller pieces
Does not change rock’s composition, only size
Examples: frost, plant rocks, road construction,mining
Weathering
Chemical Weathering
Chemical weathering – interaction of elementscreates new substance
Example: when iron rusts it reacts to oxygen in airand crumbles
Warm, moist climates produce more chemicalweathering than cool, dry
Erosion
Weathered Material Moves
Erosion occurs when weathered material is moved bywinds, water, ice, gravity
Movement grinds rock into smaller pieces, carries to newlocation
Example: water carries topsoil from hill to river, river narrows
Water Erosion
Most streams erode vertically and horizontally
A valley cut by a stream gets deeper, wider; forms v-shapedvalley
A river deposits sediment at ocean, creates delta – fan-likeform
Erosion
Wind Erosion
Wind transports sediment from one place toanother
Loess – wind-blown silt and clay sediment;produces fertile soil
Glacial Erosion
Glacier – large, long-lasting mass of ice; forms inmountainous areas
Glaciation – changing of landforms by slowlymoving glaciers
Building Soil
Soil Formation
Soil – loose mix of weathered rock, organic matter, air, water
Soil supports plant growth; fertility is dependent on 3 factors:
Texture
Amount of humus, which is organic material in soil
Amount of air and water
Soil Factors
When geographers study soil, they look at 5 factors:
Parent Material – chemical composition of original rock
Relief – steeper the slope, the greater erosion, less soil made
Organisms – plants, worms, ants, bacteria loosen soil; supplynutrients
Climate – hot, cold, wet, dry climates produce different soils
Time – about 2.5 cubic cm of soil produced each century!