Tectonic Processes & Hazards - EQ1 - 1.2C Flashcards
1
Q
The processes which occur at the plate boundaries impact on the ….. of the eruption or earthquake
A
- magnitude
2
Q
The ………. of the magma have a crucial role on the ………… and …………….. of eruptions
A
The properties of the magma have a crucial role on the magnitude and frequency of eruptions
3
Q
What are eruptions usually like at divergent boundaries
A
- Eruptions tend to be small andeffusive
- The eruptions are usually of basalt lava:
- Low gas content
- Lowviscosity
- Higher temperature
4
Q
What are earthquakes usually like at divergent boundaries
A
- Earthquakes tend to be mild and shallow
5
Q
What are earthquakes usually like at convergent boundaries
A
- Friction and pressure build up in theBenioff zone(the area within the subduction zone where most friction and pressure build up occurs)
- which causes strong earthquakes
6
Q
What are eruptions usually like at convergent boundaries
A
- Volcanic eruptions tend to be explosive as the magma is forcing its way to the surface
- These eruptions are often rhyolite lava:
- High gas content
- High viscosity
- Lower temperature
7
Q
What is tectonic activity like at transform boundaries
A
- Plates can stick causing a significant build up of pressure and powerful earthquakes
8
Q
What are the 3 types of lava
A
- basaltic lava
- andesitic lava
- rhyolitic lava
9
Q
The higher the gas level in an erruption –> the more ….
A
destructive
10
Q
What is the tectonic setting of basaltic lava
A
- Oceanic Hot Spot - Hawaii
- Constructive - Iceland
11
Q
What is the temperature of basaltic lava
A
- Hottest 1000-1200 degrees celcius
12
Q
What are the main minerals in basaltic lava
A
- low silica (50%), water, gases & aluminium
13
Q
What are the gas content of basaltic lava
A
- low 0.5-2%
14
Q
How is basaltic lava formed
A
- melting of upper mantle minerals mainly from upper zone
15
Q
What are the flow characteristics of basaltic lava
A
- thin & runny, low viscocity, gases escape
16
Q
What is the erruption energy of basaltic lava
A
- gentle, effusive
17
Q
What are the hazards of basaltic lava
A
- lava flow
18
Q
What is the silica content % of basaltic lava
A
45-55%
19
Q
Colour characteristics of basaltic lava
A
- black to dark grey
20
Q
What is the tectonic setting of andesitic lava
A
- Destructive plate margin - Andes
- Island arc margin - Montserrat
21
Q
What is the temperature of andesitic lava
A
- 800-1000 degrees celcius
22
Q
What are the main minerals in andesitic lava
A
- intermediate silica (60%), gas content, magnesium & iron
23
Q
What are the gas content of andesitic lava
A
- medium 3-4%
24
Q
How is andesitic lava formed
A
- subducted oceanic plate melts and mixes with seawater, lithospheric mantle and continental rocks
25
What are the flow characteristics of andesitic lava
* show, intermediate viscocity and traps gases
26
What is the erruption energy of andesitic lava
* violent, moderately explosive
27
What are the hazards of andesitic lava
* lava flow
* ash and tephra
* pryroclastic flow
* lahar
* gas emission
28
What is the silica content % of andesitic lava
55-65%
29
Colour characteristics of andesitic lava
* medium to dark grey
30
What is the tectonic setting of rhyolitic lava
* Continental Hot Spot - Yellowstone
* Continental Collision Zone - Himalayas
31
What is the temperature of rhyolitic lava
* coolest 600-900 degrees celcius
32
What are the main minerals in rhyolitic lava
* high silica (70%),potassium, sodium, aluminium & gas content
33
What are the gas content of rhyolitic lava
* 4-6%
34
How is rhyolitic lava formed
* melting of lithospheric mantle & slabs of previously subducted plate
35
What are the flow characteristics of rhyolitic lava
* thick & stiff, high viscocity, diffult for gases to escape
36
What is the erruption energy of rhyolitic lava
* very violent, cataclysmic
37
What are the hazards of rhyolitic lava
* cataclysmic explosion
* pryroclastic flow
38
What is the silica content % of rhyolitic lava
65-75%
39
Colour characteristics of rhyolitic lava
* light colour
40
Where are the strongest sesimic waves (earthquakes) created
* Where there is most friction and build-up of strain between two plates
* This is greatest at destructive plate margins
41
Where have the most intense earthquakes occurred
* The five recorded earthquakes of 9 or higher on the Moment Magnitude Scale (MMS) have been on destructive plate boundaries (for example, Tohoku, Japan 2011)
* Tsunamis are also more intense with this earthquake location
42
Do transform faults have strong earthquakes
* Transform faults also have earthquakes with a strong magnitude (for example, 7 on the MMS)
* as plates are trying to slide past each other leading to friction and strain
43
Where are volcanoes strongest & why?
* Volcanoes are more explosive where the magma is viscous with a high silica and gas content;
* these are found at destructive plate margins with subduction, where the subducted plate is melted, usually under a continental plate
44
Volcanoes are landforms which develop around.......
They are closely asscoiated with.......
Volcanoes are landforms which develop around **weaknesses in the earths crust where magma, gases & preexisting volcanic material are extracted**
They are closely asscoiated with **plate boundary activities**
45
What are the 3 types of volcano activity levels
* active
* dormant
* extinct
46
What are the 2 main types of volcanoes
* shield & composite
47
What is the plate boundary of shield volcanoes
constructive
48
What is an example of a shield volcano
Muana Loa, Hawaii USA
49
What is the lava type of shield volcanoes
* thinner lava - travels a long way before it cools
50
What is the structure of shield volcanoes
* gentle sides
51
What are the eruptions of shield volcanoes
* more frequent but less violent
52
What is the tectonic setting of basaltic lava
* Oceanic Hot Spot - Hawaii
* Constructive - Iceland
53
What is the temperature of basaltic lava
* Hottest 1000-1200 degrees celcius
54
What are the main minerals in basaltic lava
* low silica (50%), water, gases & aluminium
55
What are the gas content of basaltic lava
* low 0.5-2%
56
How is basaltic lava formed
* melting of upper mantle minerals mainly from upper zone
57
What are the flow characteristics of basaltic lava
* thin & runny, low viscocity, gases escape
58
What is the erruption energy of basaltic lava
* gentle, effusive
59
What are the hazards of basaltic lava
* lava flow
60
What is the silica content % of basaltic lava
45-55%
61
Colour characteristics of basaltic lava
* black to dark grey
62
What is the plate boundary of composite volcanoes
destructive
63
What is an example of a composite volcano
Mount St. Helens, Washington USA
64
What is the lava type of composite volcanoes
* viscous magma, trap hot gas & large amounts of water
65
What is the structure of composite volcanoes
* coneshape, layered steep sides
66
What are the eruptions of composite volcanoes
* not frequent but very violent
67
Explain how magma comes to be lava
* Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma
* Since it is lighter than the solid rock around it, magma rises and collects in magma chambers
* Eventually, some of the magma pushes through vents and fissures to the Earth's surface
* Magma that has erupted is called lava
68
# Non-violent eruptions
The explosivity of an eruption depends on the....
composition of the magma
69
# Non-violent eruptions
If magma is thin and runny,................... easily from it.
When this type of magma erupts, it......
A good example is the eruptions at........
* gases can escape
* flows out of the volcano
* Hawaii's volcanoes
70
# Non-violent eruptions
Lava flows rarely kill people because...
* they move slowly enough for people to get out of their way
71
How do violent erruptions occur
* If magma is thick and sticky, gases cannot escape easily
* Pressure builds up until the gases escape violently and explode
72
What is a good example of violent eruptions
* The eruption of Washington's Mount St. Helens
73
What is tephra
* In violent eruptions (possibly of andestic lava), the magma blasts into the air and breaks apart into pieces called tephra
* Tephra can range in size from tiny particles of ash to house-size boulders
74
What is the VEI
* The VEl is a relative measure of the explosiveness of a volcanic eruption,
* the scale that enables explosive volcanic eruptions to be compared with one another
75
What does VEI stand for
Volcanic explosiveness index
76
Why is the VEI valuable
* It is very valuable because it can be used for both:
* recent eruptions that scientists have witnessed
* & historic eruptions that happened thousands to millions of years ago
77
What is the VEI based on
* The volume of tephra (ash) produced during an eruption and uses the following factors to assign a number:
- The amount of the volcanic material ejected (tephra and ash falls etc)
- How long the eruption lasts
- Height of eruption cloud
- Qualitative descriptive terms (such as 'gentle', 'explosive', etc.)
