Tectonics Flashcards
Wegners climatological evidence
Coal which must have been formed in tropical conditions found in Uk, Antarctica and USA
Wegners geological evidence
Glacial deposits found in India South America and Antarctica
Striations in same directions in Brazil and west Africa
Wegners continental evidence
Appeared fit of the continents and shorelines
Seen as Africa and South America
Two types of constructive margin
Oceanic-oceanic
Continental- continental
Plates move apart
Landform found at oceanic divergent boundaries + example
Oceanic ridges
Mid Atlantic ridge as North American plate moves away from Eurasian plate
How are oceanic ridges formed?
Constructive oceanic plate boundary
As plate moves apart at vary rates, the crust expands and becomes weaker
Increased heat at the surface and eventually the brittle crust subsidies into magma and forms ridge
Landform at continental divergence and example
Rift valleys
East African Rift Valley
Nubian-Somalian
How are Rift Valleys made?
As 2 continental plates move apart the brittle crust fractures and sinks at parallel faults towards the lithosphere
Form, lava type and eruption style of volcanoes at oceanic divergent boundary + example
VEI
Lava plateaux/fissure Basaltic Icelandic Typically submarine volcanoes but can reach surface Surtsey VEI:0-2
Wegners biological evidence
Fossils of Mesosaurus found in South America and South Africa with migration unlikely
Volcanicity at continental divergent margins
Example Mount Kilimanjaro Form: basic shield volcano Lava: basaltic Eruption: Hawaiian possibly Vesuvian VEI: 0-2
Volcanicity at continental divergent margins
Example Mount Kilimanjaro Form: basic shield volcano Lava: basaltic Eruption: Hawaiian possibly Vesuvian VEI: 0-2
What is a transform fault?
90 degrees to plate boundary as new crust is formed
As pressure builds can result in an earthquake
Can earth quakes occur at divergent plate boundaries?
Yes
3 types of destructive plate boundary
Oceanic-oceanic
Oceanic-continental
Continental-continental
Landforms at O-C destructive boundary
Deep sea trench
Fold mountains
How are deep sea trenches formed?
O-C destructive
O-o destructive
Peru chile trench as max a subducted under South American
Marianas trench as Pacific subducted under Philippine
How are fold mountains formed
O-C destructive
C-C destructive margins
As plates come together sediments are deformed by faulting and forming and are uplifted to form fold mountains
What is the Benioff zone?
Part of the subduction zone
Point at which the oceanic plate is melted/ destroyed
Volcanic activity at O-c destructive margins
Oceanic plate descends towards the mantle and becomes hotter
Increased friction also increases heat
Results in plate melting
Lava erupted in gaps in crust in volcanoes
Why is lava andesitic at o-c destructive margins
Oceanic plate melts which is typically basaltic but it combines with older elements of the crust which have a higher silica content
Form Lava type Eruption style VEI Volcanoes at O-C destructive margins
Composite cone or ash and cinder cones
Andesitic lava
Peléan eruptions
VEI 4-6
What % of active volcanoes are found at subduction zones
80
Do earthquakes occur at O-O destructive margins
Yes typically shallow focus
Very powerful
Up to magnitude 9
Is there volcanic activity at C-C destructive margins
No as no subduction
Few earthquakes occur
What are conservative plate margins
Plates move parallel to the boundary
No crust is made or destroyed
No volcanic activity
Pressure builds and released as earthquakes
Example of a conservative plate boundary
San Andreas fault California
Pacific against North American
What are hotspots
Volcanic activity that does not occur at plate boundary
Concentration of radioactive elements increases heat
Generates convection currents
More magma near surface eats into plate above
Lava breaks into surface
Is a hotspot stationary or moving?
Stationary
Where are volcanoes found
Oceanic ridges
Oceanic trenches:/ subduction zone
Rift Valleys
Hotspots
What is intrusive volcanic activity
Magma which is viscous does not reach surface and cools and intrudes the crust to form features
How are intrusive features exposed
Erosion and weathering
Batholith formation
Large mass of magma cools and solidifies
Forms granite crystals in Igneous rock
Formed as a dome
Example of a batholith
Dartmoor
Isle of Arran
What is a metamorphic aureole?
During batholith formation the surrounding rock is altered by heat and pressure of the magma intrusion
Dynamics of rock change eg limestone to marble
Laccoliths
Small injections of magma in rock strata
Causes the rock to arch upwards
Forms a lens shape
Example of a laccoliths
Eildon hills Scotland
What is a dyke
Vertical intrusion with horizontal cooling cracks
Magma shoots upwards when forming a batholith
Cut across the bedding Plane of rock which has been previously intruded
Collection of dykes
Dyke swarm
Example of a dyke
Isle of Skye
What are sills
Horizontal intrusions with vertical cooling cracks
Run along the bedding plane
Example of a Sill
Great Whin Sill Scotland
What are extrusive landforms
Molten rock reaches the surface
Solfatara
Example
Gases mainly sulfur escape onto the surface from a dormant volcano
Bay of Naples, Italy
Geysers
Large discharge of water followed by steam
Water is heated by the contact with hot rock and then constricted and pressurised
Plumbing system allows a jet of water
Old Faithful Yellowstone
Mud volcanoes
Deposition of hot water and mud onto the surface, not dangerous
Philippines
Fumaroles
Superheated water changes state into steam as a result of a large pressure decrease
Gases such as CO2 and SO2 released
Examples of intrusive and extrusive activity in the UK
Granites
Dykes and sills
Basaltic flows
Volcanic plug
Granites in UK
Intruded rock in the Grampians
Batholiths exposed
Tors made= distinctive landscape
Dykes and sills in the UK
More resistant than surrounding rock
Great Whin
Basaltic flows UK
Antrim lava plateaux in N Ireland
Volcanic plug UK
Long extinct volcano found in Edinburgh
Active 300mn years ago
Primary impacts of volcanic activity
Tephra
Pyroclastic flows
Lava
Volcanic gases
What is tephra
Solid material ejected from a volcano
Range from ash to volcanic bombs
Pyroclastic flows
Gas charged, high velocity flows of tephra and gas
Examples of volcanic gases
Example
Sulfur dioxide Carbon dioxide Carbon monoxide Chlorine 1700 suffocated in Nyos Cameroon
Example of volcanic gases
1986 Nyos Cameroon 1700 suffocated
What are lahars?
Volcanic Mud flows
Example of lahars
Village of Amero Colombia destroyed in 1985
Why is flooding a secondary effect of volcanoes and example
Melting of glaciers Iceland 1996
Example of volcanic tsunami
Krakatoa 1883 36,000 people drowned
Example of climate change due to volcanoes
Krakatoa caused 0.5degree global drop in temperature
Final secondary effect
Landslides
Focus of earthquake
point at which the pressure of plate movement has been released
Epicentre of an earthquake
Point directly above the focus on the earths surface
Depth of a shallow focus
0-70km
Which waves travel fastest
p
Movement of P waves
Compressional
Vibrate in direction that they travel
Which of the Earth’s layers can P waves travel through
Mantle and core
Can P waves travel through solids, liquids or both
Both
At what speed do s waves travel
1/2 speed of P
Movement of S waves
shear rock as they vibrate at 90 degrees to the direction of travel
Can S waves travel through solids, liquids or both
Solids only
Which of the Earth’s layers can S waves travel through
Mantle
2 types of surface wave
Love and Rayleigh
Speed of Surface waves
travel slowest and nearest to the Earth’s surface
Describe L waves
travel through solids only and move side to side and result in rock shearing
Describe Rayleigh waves
Travel in a rolling motion and through liquids and solids
What are the 4 causes of earthquakes
Plate Movement, Reactivation of old fault lines, subsidence and pressure on rocks through reservoirs and fracking
Example of reactivation of fault line quake in Uk
4.8 in Birmingham 23/09/2002
Are destructive or constructive earthquakes the most powerful
Destructive
Describe the Richter Scale
Logarithmic scale where an increase of 1 on the scale translates to 10 higher amplitude and 31 times more energy released
Mercalli Scale
measures the intensity of an earthquake using observations eg photos to assess the damage caused
