Tectonic Processes and Hazards - Set 1 Flashcards
1
Q
Earths internal structure
A
- Crust = 0-100km thick
- Asthenosphere
- mantle
- outer core = liquid
- Inner core Solid
2
Q
Oceanic crust
A
- Basalt rock
- up to 10km Thick = thin
- Dense at 3.0g/cm3
- Newer
3
Q
Continental crust
A
- Less dense at 2.6g/cm3
- Light coloured granite
- Up to 50km thick = thick
- Older
4
Q
Convection
A
Created in the mantle - Heat moves away from inner core - Mantle becomes more viscous under heat and pressure
5
Q
Frictional drag
A
- Convection cells make contact with the base of the crust - moves the plates by frictional drag
6
Q
Slab pull
A
Denser oceanic plates subducted at cold dwellings
7
Q
Convergent (Destructive)
A
- Oceanic and Continental plates
- Oceanic plate slides underneath continental as is more dense - Forms fold mountains
8
Q
Convergent (Destructive)
A
- Oceanic and Oceanic
- The densest is subducted beneath the other - forms volcanoes
9
Q
Convergent (Collision)
A
- Continental and Continental
- Collision margin occurs when they meet as both have same density - Sediments between them are crumpled which forms high-fold mountains e.g. Himalayas
10
Q
Divergent (Constructive)
A
- 2 plates move apart and new crust is created - creates ocean ridges
11
Q
Conservative (Transform)
A
- Plates slide past each other which creates a break in the crust = fault
- e.g. San Andres fault
12
Q
Plate numbers
A
- 7 Major plates
- 10 Minor plates
- 50 Micro plates
13
Q
Why is Asthenosphere
A
Weak layer which has plastic, molten properties - allow the Lithosphere to slide over the the asthenosphere - Without this Major plates would not be able to move making the plate tectonic theory impossible
14
Q
Volcanic hotspots theory’s
A
1 - Mantle plumes = Heat rising from mantle under mid-ocean ridge
2 - Lithosphere becomes weakened, allowing magma to flow to surface
15
Q
Primary hazards of Volcanoes - Pyroclastic flows
A
- Magma froths in vent of volcano - bubbles burst ejecting hot gases and pyroclastic materials (e.g. Glass)
- Clouds up to 1000 degrees
- Responsible for most volcanic deaths
16
Q
Primary hazards of Volcanoes - Tephra
A
- Rock fragments ejected into atmosphere
- Bombs and dust
- Cause buildings to collapse and start fires
17
Q
Primary hazards of Volcanoes - Lava flows
A
- Viscosity determined by volume of Silicon dioxide in it
- Worst in 1873 where flowed for 5 months in Iceland and killed 22% of Pop. due to famine
18
Q
Primary hazards of Volcanoes - Volcanic gases
A
- Contain Sulphur dioxide and Carbon monoxide
- Carbon monoxide biggest killer as is invisible
- 1986 emissions from Lake Nyos killed 1700
19
Q
Fumaroles
A
Opening in the planets crust which emits gases such as CO2
20
Q
Secondary hazards of Volcanoes - Lahar
A
- Volcanic mudflows
- Depends on slope angle and material etc
21
Q
Secondary hazards of Volcanoes - Jokulhlaup
A
- Glacial outburst floods
- Cause widespread land modification through erosion and deposition
22
Q
Types of volcano
A
- Shield and Strato volcanoes
- Strato more explosive
23
Q
Volcanic Explosivity Index (VEI)
A
0 - Nonexplosive = Daily
4 - Cataclysmic = every 10 years
8 - Mega colossal = every 10,000 years
- Measured by Plume size and volume height
24
Q
Types of Lava
A
- Andesitic = Slow, Violent and 1000 degrees
- Basaltic = Runny, Gentle and 1200 degrees
- Rhyolitic = Stiff, Violent and 8000 degrees
25
Decade Volcanoes
-Chosen to be monitored in 1960s - 16 Volcanoes which had histories of violent eruptions - allows for nearby pop. to be evacuated if a threat emerges
26
Different measures to monitor Volcanic eruptions
- Seismicity
- Gas emissions - CO2 main gas emitted
- Ground deformation
27
Plate boundary
When two tectonic plates meet
28
Plate margin
Areas adjacent to plate boundaries
29
Wegner - 1915
- Found Mountain ranges had similar rock types and Fossils of animals found in different continents
- Couldn't explain why
30
WW1
Development of the Sonar - Showed Ocean floor was not flat and featureless
31
Arthur Holmes - 1919
- Theory that convection in mantle causes plates to move
- Proposed convection currents move through mantle like air moves through a room
32
1954
World map of volcanic eruptions and earthquakes reveals a worldwide pattern
33
Hess and Dietz
- Idea of sea-floor spreading magma oozes up from earths interior along mid ocean ridges - creates a new sea floor
34
Wilson - 1965
Idea earths crust is made of plates
35
1983
GPS made available to public - could track movement of earth's surface
36
What is a seismic wave
Vibration through the earths crust which causes surface to oscillate
37
Wave types
- P wave = Primary - caused by compression and travel at 8km/sec
- S wave = Secondary - vibrate at 90 degree angle to direction of travel - 4km/sec
- L wave = Love - Fastest surface wave - S and L waves most destructive
38
Secondary Hazards of Earthquakes - Soil Liquefication
Water saturated material behaves like a liquid - earthquakes cause water pressure to increase which allows soil particles to move easily
39
Secondary Hazards of Earthquakes - Landslides
- Magnitude of 4+ can cause a landslide
40
Hypocentre
Focus point within the ground where the strain energy of the earthquake stored in the rock is first released
41
Wadati-Benioff zone
Area of seismicity corresponding with the slab being thrust down in a subduction zone
42
Secondary Hazards of Earthquakes - Tsunami
- Sequence of waves with deep troughs in-between - Short water = more friction = waves slow and increase in amplitude
- Created by water column displacement
- 90% found in the Pacific Basin
43
Tsunamis key terms
- Long wavelength = 1000km
- Low amplitude = 5m
- Fast velocity = 6000 km/hr
44
Mercalli scale
- Measures the experienced impacts of an earthquake
- Very subjective
45
Richter Scale
- Measures amplitude of waves - rates them from 0-9
46
Moment magnitude scale
- Describes Earthquakes in terms of energy released
47
Vulnerability
Potential for a population to be harmed
48
Difference between forecasting and predicting
- Forecasting = using data from previous natural hazards
- Predicting = Indication that a hazard will happen without previous data
49
How do Culture and Attitudes influence Vulnreability to natural hazards
Japanese Tsunami 2011 - responded rapidly and areas completely restored within months
50
Losses greater for poorer groups
During Hurricane Mitch, The poor lost 18% of their value and 40% of crop value compared to 3% and 25% for wealthier groups
