Saturday, September 24, 2005
GEOG - PLATE TETONICS & RESULTING LANDFORMS
OCEANIC___________________CONTINENTAL
Sima (silicon + magnesium)_______Sial (silicon + aluminium)
Mainly basaltic________________Mainly granite
Thinner (5-10km)______________Thicker (35-40. 60-70km under mountain )
Denser (3g/cm3)_______________Less Dense (2.7g/cm3)
Younger_____________________Older
More continuous_______________Less continuous
Continental Drift – Alfred Wegner: started as Pangaea, drifted apart, formed current continents
-cause: convection currents-magma in mantle heats up, expands & rises, spread outs, cools, sinks, repeat
Evidence: 1. coastlines of continents fit together like jigsaw puzzle pieces (e.g. Africa and South America)
2. similar fossil of reptile found (e.g. Africa and South America)
3. identical fossil fern found (all southern continents)
4. rocks of same age and geological structure ( e.g. SW Africa and SE Brazil)
5. coal (which is formed under warm and wet conditions) found under Antarctic icecap
Plate Movements
Divergent (O&O): plates move apart
-tensional stresses cause fractures to occur
é new basaltic magma wells up, some melt
é erupts on surface as lava
é inject near the surface
é crystallize as igneous rocks
é become new sea floor, sea floor spreading
é forms oceanic ridges
é more basaltic magma piles up and solidifies
é forms a chain of mountains
é plates continue to move apart
é mountain move away from spreading zone
é youngest closest and oldest furthest
é earthquakes occur, volcanic activity
é basaltic magma escapes up fractures
é form submarine rift volcanoes
C&C: plates move apart
é faulting occurs, causes earthquake
é no new crust form
é formation of new sea (e.g. red sea)
é magma flows up cracks in crust
é volcanoes formed
Convergent (O&O):plates edges bent into deep oceanic trench [e.g. Marianas Trench in Pacific Ocean (Pacific plate dives below Philippines)]
é plate with lower percentage of continental crust would subduct
é subduction zone, subducting plate melts under high heat and friction
é silica-rich magma produced
é form chain of subduction volcanoes- island arc
é earthquake occurs: downward movement of subducting plate is not smooth
O&C: thinner and denser oceanic plate subducts
é long, narrow and deep oceanic trench is formed (e.g. Peru-Chile Trench off South American coast)
é faulting occurs, earthquake occurs
é downwards movement of plate not smooth
é subducting plate melts under high heat and friction, silica-rich magma formed
é being less dense, magma rises up fractures
é escapes through vents to the land surface
é forms subduction volcanoes
é continental late contorted and folded
é form fold mountains
C&C: no subduction
é one may be pushed under the other for a short distance
é both light and buoyant, no volcanic activity
é folding occurs, produce great uplift and highly contorted fold mountain ranges
é e.g. Himalayan Mountains (Indo-Australian and Eurasian)
é faulting and earthquakes
Transform: same direction @ diff speeds
é Pacific Plate and North American plate along the San Andreas Fault
é lithospheric material neither created not destroyed
é plates moving in different directions
é jerky movements causes earthquakes
é no volcanic activity
fold mountains: fold is a bend in rock strata
anticline: hill syncline: valley
folds: 1. simple fold: limbs with same steepness
2. asymmetrical fold: uneven limbs, uneven forces
3. overfold: both limbs sloping in same direction
4. recumbent fold: axis of fold is almost horizontal
5. overthrust fold: fractured recumbent fold
Circum pacific region: rocky mtns & andes, island arcs (japan & the philippines)
Eurasion Indonesian belt: atlas mtns Africa; alps southern Europe; Himalayas northern India
Himalayas mtns: indo-australian & Eurasian plates
-tethys sea separating India & asia subducted under Eurasian plate
-when asia & India continental mass met, folding of sediments occurred as there was no subduction
Andes mtns: nazca & south American plates
-oceanic nazca sinks under continental SA plate, being thinner and denser
-sediment on the ocean floor squeezed & crumpled
-silica rich magma rose thru fractures: subduction vol
Faulting: break or fracture in rocks where they are displaced. caused by stresses & strains
1. normal fault: tension; lithosphere is pulled apart
- one blocked lowered; forms steep scarp/cliff
2. reverse fault: compression; one block rises, forms overhanging escarpment which may be eroded
3. transform fault: adjacent blocks slide past horizontally along the fracture
Horst(block mtn): uplifted block w/ steep fault scarps
-caused by tension or compression
Tilt block: block mtn w one scarp
Rift valley/graben: elongated deep valley
-caused by tension or compression
-parallel faults form stepped scarps
-magma rises to form rift volcanoes at sides
Lava: lower silica content >higher temperature & more fluid
Basic: low silica content, fluid, rich in iron & magnesium, hot abt 1200oC, flows slowly & far
-produced at constructive boundaries
-quiet explosion as it allows expanding gases to escape easily thru the vent
-forms gently sloping volcanoes 2o-10o
Acid: high silica content, viscous, not so hot 800oC, solidifies quickly, does not flow far
-produced at destructive boundaries
-violent explosion as lava solidifies quickly & blocks the upward movement of expanding gases
-forms steep sided volcanoes
Lava plateau: built up by basaltic lava frm fissures
-spread ovr large area, solidifies: Columbia plateau
Volcano: 1. conical or dome shaped
2. crater: throws out gases, pyroclasts & lava
-enlarged crater (>1kmD) caldera; may contain lake
-caldera formed when removal of magma is faster than it can be replenished so summit collapses into magma chamber of volcano
3. magma flows frm magma chamber to pipe to vent
4. composite volcano may have a secondary cone
Active: erupts frequently & in recent times
Dormant: not erupted recently but not extinct
Extinct: does not erupt anymore
Formation: magma rises up fractures in rocks; pressure is reduced when it moves upwards: allows gases to expand & volcanic material to be ejected
-volcanic material piles up arnd vent, forms volcano
Gases: steam, carbon dioxide, sulphur dioxide
Solids: ash, dust, volcanic bombs, cinder (pyroclasts)
types: 1. ash & cinder volcano: steep sided, gentle base symmetrical; formed frm hot ash & red hot cinders; bowl shaped summit crater
2. basic lava volcano(shield):wide base gentle slopes
Hot spot volcanoes: mauna loa in Hawaii
-far away frm plate boundary
Basaltic magma issues thru a vent to form volcano
-plate moves, chain of volcanic islands formed
3. lava dome: acid lava too viscous & solidifies ovr vent to form a bulbous structure. Sides become steep and dome shaped when lava fills up the interior
4. volcanic plug: viscous acid lava solidified in central pipe and forms a spine or volcanic plug
5. composite volcano: alternate layers of pyroclasts & viscous acid lava; steeper towards top, gentler at base – composite cones formed when lava flows out of secondary pipes
6. minor features associated with vulcanicity
a. volcanic hot spring
b. geyser: violent ejection of hot water
problems: 1. massive destruction: of lives & property; interrupt communication; gases (CO2) suffocate ppl
2. tsunamis: eruptions near coast create huge waves
3. pollution: damage respiratory systems; contaminate water sources
4. steam affects rain; sulphur affects ozone layer
Benefits: 1. weathered volcanic materials make good fertile soil with necessary minerals for cultivation
2. precious stones & minerals: mining
3. tourism: hot springs resorts, attractions
4. geothermal energy (heat below earth’s surface): produce electricity, warm houses
Earthquakes: occurs when energy built up in earth’s crust is suddenly released
-occurs when convergent movement is not smooth
-stress in rocks so great that causes the ground to vibrate when the rocks jerk free
1. focus: source of earthquake
2. epicentre: point on surface directly above focus
3. seismic waves: measured by seismograph
4. Richter scale0-9: measure amt of energy released
Problems: 1. destroy buildings & roads : toppled over, hinders rescue work
2. disrupts water, gas & electricity supplies & communication: burst pipes, broken telephone lines; fires formed, diseases rampant -water contaminated
3. causes landslides & tsunamis
Factors affecting extent of damage: 1. magnitude
2. depth of focus: shallow focus, large extent
3. epicentre: nearer, larger damage; more solid rock epicentre, less damage
4. constructions: dense built up buildings, more damage; flimsy old building cannot withstand
5. forecast: prediction & preparation help
6. tsunamis: no tsunami, less damage
Ways to reduce damage: 1. location, design & materials of buildings: don’t build on active fault zone;unstable soil, use shock absorbing rubber blocks
2. limit outbreak of fires: use fireproof materials
3. conduct drills; preparation: familiarise people with emergency procedures; have enough supplies
4. prediction & warning systems
Sima (silicon + magnesium)_______Sial (silicon + aluminium)
Mainly basaltic________________Mainly granite
Thinner (5-10km)______________Thicker (35-40. 60-70km under mountain )
Denser (3g/cm3)_______________Less Dense (2.7g/cm3)
Younger_____________________Older
More continuous_______________Less continuous
Continental Drift – Alfred Wegner: started as Pangaea, drifted apart, formed current continents
-cause: convection currents-magma in mantle heats up, expands & rises, spread outs, cools, sinks, repeat
Evidence: 1. coastlines of continents fit together like jigsaw puzzle pieces (e.g. Africa and South America)
2. similar fossil of reptile found (e.g. Africa and South America)
3. identical fossil fern found (all southern continents)
4. rocks of same age and geological structure ( e.g. SW Africa and SE Brazil)
5. coal (which is formed under warm and wet conditions) found under Antarctic icecap
Plate Movements
Divergent (O&O): plates move apart
-tensional stresses cause fractures to occur
é new basaltic magma wells up, some melt
é erupts on surface as lava
é inject near the surface
é crystallize as igneous rocks
é become new sea floor, sea floor spreading
é forms oceanic ridges
é more basaltic magma piles up and solidifies
é forms a chain of mountains
é plates continue to move apart
é mountain move away from spreading zone
é youngest closest and oldest furthest
é earthquakes occur, volcanic activity
é basaltic magma escapes up fractures
é form submarine rift volcanoes
C&C: plates move apart
é faulting occurs, causes earthquake
é no new crust form
é formation of new sea (e.g. red sea)
é magma flows up cracks in crust
é volcanoes formed
Convergent (O&O):plates edges bent into deep oceanic trench [e.g. Marianas Trench in Pacific Ocean (Pacific plate dives below Philippines)]
é plate with lower percentage of continental crust would subduct
é subduction zone, subducting plate melts under high heat and friction
é silica-rich magma produced
é form chain of subduction volcanoes- island arc
é earthquake occurs: downward movement of subducting plate is not smooth
O&C: thinner and denser oceanic plate subducts
é long, narrow and deep oceanic trench is formed (e.g. Peru-Chile Trench off South American coast)
é faulting occurs, earthquake occurs
é downwards movement of plate not smooth
é subducting plate melts under high heat and friction, silica-rich magma formed
é being less dense, magma rises up fractures
é escapes through vents to the land surface
é forms subduction volcanoes
é continental late contorted and folded
é form fold mountains
C&C: no subduction
é one may be pushed under the other for a short distance
é both light and buoyant, no volcanic activity
é folding occurs, produce great uplift and highly contorted fold mountain ranges
é e.g. Himalayan Mountains (Indo-Australian and Eurasian)
é faulting and earthquakes
Transform: same direction @ diff speeds
é Pacific Plate and North American plate along the San Andreas Fault
é lithospheric material neither created not destroyed
é plates moving in different directions
é jerky movements causes earthquakes
é no volcanic activity
fold mountains: fold is a bend in rock strata
anticline: hill syncline: valley
folds: 1. simple fold: limbs with same steepness
2. asymmetrical fold: uneven limbs, uneven forces
3. overfold: both limbs sloping in same direction
4. recumbent fold: axis of fold is almost horizontal
5. overthrust fold: fractured recumbent fold
Circum pacific region: rocky mtns & andes, island arcs (japan & the philippines)
Eurasion Indonesian belt: atlas mtns Africa; alps southern Europe; Himalayas northern India
Himalayas mtns: indo-australian & Eurasian plates
-tethys sea separating India & asia subducted under Eurasian plate
-when asia & India continental mass met, folding of sediments occurred as there was no subduction
Andes mtns: nazca & south American plates
-oceanic nazca sinks under continental SA plate, being thinner and denser
-sediment on the ocean floor squeezed & crumpled
-silica rich magma rose thru fractures: subduction vol
Faulting: break or fracture in rocks where they are displaced. caused by stresses & strains
1. normal fault: tension; lithosphere is pulled apart
- one blocked lowered; forms steep scarp/cliff
2. reverse fault: compression; one block rises, forms overhanging escarpment which may be eroded
3. transform fault: adjacent blocks slide past horizontally along the fracture
Horst(block mtn): uplifted block w/ steep fault scarps
-caused by tension or compression
Tilt block: block mtn w one scarp
Rift valley/graben: elongated deep valley
-caused by tension or compression
-parallel faults form stepped scarps
-magma rises to form rift volcanoes at sides
Lava: lower silica content >higher temperature & more fluid
Basic: low silica content, fluid, rich in iron & magnesium, hot abt 1200oC, flows slowly & far
-produced at constructive boundaries
-quiet explosion as it allows expanding gases to escape easily thru the vent
-forms gently sloping volcanoes 2o-10o
Acid: high silica content, viscous, not so hot 800oC, solidifies quickly, does not flow far
-produced at destructive boundaries
-violent explosion as lava solidifies quickly & blocks the upward movement of expanding gases
-forms steep sided volcanoes
Lava plateau: built up by basaltic lava frm fissures
-spread ovr large area, solidifies: Columbia plateau
Volcano: 1. conical or dome shaped
2. crater: throws out gases, pyroclasts & lava
-enlarged crater (>1kmD) caldera; may contain lake
-caldera formed when removal of magma is faster than it can be replenished so summit collapses into magma chamber of volcano
3. magma flows frm magma chamber to pipe to vent
4. composite volcano may have a secondary cone
Active: erupts frequently & in recent times
Dormant: not erupted recently but not extinct
Extinct: does not erupt anymore
Formation: magma rises up fractures in rocks; pressure is reduced when it moves upwards: allows gases to expand & volcanic material to be ejected
-volcanic material piles up arnd vent, forms volcano
Gases: steam, carbon dioxide, sulphur dioxide
Solids: ash, dust, volcanic bombs, cinder (pyroclasts)
types: 1. ash & cinder volcano: steep sided, gentle base symmetrical; formed frm hot ash & red hot cinders; bowl shaped summit crater
2. basic lava volcano(shield):wide base gentle slopes
Hot spot volcanoes: mauna loa in Hawaii
-far away frm plate boundary
Basaltic magma issues thru a vent to form volcano
-plate moves, chain of volcanic islands formed
3. lava dome: acid lava too viscous & solidifies ovr vent to form a bulbous structure. Sides become steep and dome shaped when lava fills up the interior
4. volcanic plug: viscous acid lava solidified in central pipe and forms a spine or volcanic plug
5. composite volcano: alternate layers of pyroclasts & viscous acid lava; steeper towards top, gentler at base – composite cones formed when lava flows out of secondary pipes
6. minor features associated with vulcanicity
a. volcanic hot spring
b. geyser: violent ejection of hot water
problems: 1. massive destruction: of lives & property; interrupt communication; gases (CO2) suffocate ppl
2. tsunamis: eruptions near coast create huge waves
3. pollution: damage respiratory systems; contaminate water sources
4. steam affects rain; sulphur affects ozone layer
Benefits: 1. weathered volcanic materials make good fertile soil with necessary minerals for cultivation
2. precious stones & minerals: mining
3. tourism: hot springs resorts, attractions
4. geothermal energy (heat below earth’s surface): produce electricity, warm houses
Earthquakes: occurs when energy built up in earth’s crust is suddenly released
-occurs when convergent movement is not smooth
-stress in rocks so great that causes the ground to vibrate when the rocks jerk free
1. focus: source of earthquake
2. epicentre: point on surface directly above focus
3. seismic waves: measured by seismograph
4. Richter scale0-9: measure amt of energy released
Problems: 1. destroy buildings & roads : toppled over, hinders rescue work
2. disrupts water, gas & electricity supplies & communication: burst pipes, broken telephone lines; fires formed, diseases rampant -water contaminated
3. causes landslides & tsunamis
Factors affecting extent of damage: 1. magnitude
2. depth of focus: shallow focus, large extent
3. epicentre: nearer, larger damage; more solid rock epicentre, less damage
4. constructions: dense built up buildings, more damage; flimsy old building cannot withstand
5. forecast: prediction & preparation help
6. tsunamis: no tsunami, less damage
Ways to reduce damage: 1. location, design & materials of buildings: don’t build on active fault zone;unstable soil, use shock absorbing rubber blocks
2. limit outbreak of fires: use fireproof materials
3. conduct drills; preparation: familiarise people with emergency procedures; have enough supplies
4. prediction & warning systems
# we mugged! @ 5:31 AM 
