Tectonic Processes & Hazards - EQ1 - 1.2C Flashcards
The processes which occur at the plate boundaries impact on the ….. of the eruption or earthquake
- magnitude
The ………. of the magma have a crucial role on the ………… and …………….. of eruptions
The properties of the magma have a crucial role on the magnitude and frequency of eruptions
What are eruptions usually like at divergent boundaries
- Eruptions tend to be small andeffusive
- The eruptions are usually of basalt lava:
- Low gas content
- Lowviscosity
- Higher temperature
What are earthquakes usually like at divergent boundaries
- Earthquakes tend to be mild and shallow
What are earthquakes usually like at convergent boundaries
- 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
What are eruptions usually like at convergent boundaries
- 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
What is tectonic activity like at transform boundaries
- Plates can stick causing a significant build up of pressure and powerful earthquakes
What are the 3 types of lava
- basaltic lava
- andesitic lava
- rhyolitic lava
The higher the gas level in an erruption –> the more ….
destructive
What is the tectonic setting of basaltic lava
- Oceanic Hot Spot - Hawaii
- Constructive - Iceland
What is the temperature of basaltic lava
- Hottest 1000-1200 degrees celcius
What are the main minerals in basaltic lava
- low silica (50%), water, gases & aluminium
What are the gas content of basaltic lava
- low 0.5-2%
How is basaltic lava formed
- melting of upper mantle minerals mainly from upper zone
What are the flow characteristics of basaltic lava
- thin & runny, low viscocity, gases escape
What is the erruption energy of basaltic lava
- gentle, effusive
What are the hazards of basaltic lava
- lava flow
What is the silica content % of basaltic lava
45-55%
Colour characteristics of basaltic lava
- black to dark grey
What is the tectonic setting of andesitic lava
- Destructive plate margin - Andes
- Island arc margin - Montserrat
What is the temperature of andesitic lava
- 800-1000 degrees celcius
What are the main minerals in andesitic lava
- intermediate silica (60%), gas content, magnesium & iron
What are the gas content of andesitic lava
- medium 3-4%
How is andesitic lava formed
- subducted oceanic plate melts and mixes with seawater, lithospheric mantle and continental rocks
What are the flow characteristics of andesitic lava
- show, intermediate viscocity and traps gases
What is the erruption energy of andesitic lava
- violent, moderately explosive
What are the hazards of andesitic lava
- lava flow
- ash and tephra
- pryroclastic flow
- lahar
- gas emission
What is the silica content % of andesitic lava
55-65%
Colour characteristics of andesitic lava
- medium to dark grey
What is the tectonic setting of rhyolitic lava
- Continental Hot Spot - Yellowstone
- Continental Collision Zone - Himalayas
What is the temperature of rhyolitic lava
- coolest 600-900 degrees celcius
What are the main minerals in rhyolitic lava
- high silica (70%),potassium, sodium, aluminium & gas content
What are the gas content of rhyolitic lava
- 4-6%
How is rhyolitic lava formed
- melting of lithospheric mantle & slabs of previously subducted plate
What are the flow characteristics of rhyolitic lava
- thick & stiff, high viscocity, diffult for gases to escape
What is the erruption energy of rhyolitic lava
- very violent, cataclysmic
What are the hazards of rhyolitic lava
- cataclysmic explosion
- pryroclastic flow
What is the silica content % of rhyolitic lava
65-75%
Colour characteristics of rhyolitic lava
- light colour
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
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
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
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
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
What are the 3 types of volcano
- active
- dormant
- extinct
What are the 2 main types of volcanoes
- shield & composite
What is the plate boundary of shield volcanoes
constructive
What is an example of a shield volcano
Muana Loa, Hawaii USA
What is the lava type of shield volcanoes
- thinner lava - travels a long way before it cools
What is the structure of shield volcanoes
- gentle sides
What are the eruptions of shield volcanoes
- more frequent but less violent
What is the tectonic setting of basaltic lava
- Oceanic Hot Spot - Hawaii
- Constructive - Iceland
What is the temperature of basaltic lava
- Hottest 1000-1200 degrees celcius
What are the main minerals in basaltic lava
- low silica (50%), water, gases & aluminium
What are the gas content of basaltic lava
- low 0.5-2%
How is basaltic lava formed
- melting of upper mantle minerals mainly from upper zone
What are the flow characteristics of basaltic lava
- thin & runny, low viscocity, gases escape
What is the erruption energy of basaltic lava
- gentle, effusive
What are the hazards of basaltic lava
- lava flow
What is the silica content % of basaltic lava
45-55%
Colour characteristics of basaltic lava
- black to dark grey
What is the plate boundary of composite volcanoes
destructive
What is an example of a composite volcano
Mount St. Helens, Washington USA
What is the lava type of composite volcanoes
- viscous magma, trap hot gas & large amounts of water
What is the structure of composite volcanoes
- coneshape, layered steep sides
What are the eruptions of composite volcanoes
- not frequent but very violent
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
Non-violent eruptions
The explosivity of an eruption depends on the….
composition of the magma
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
Non-violent eruptions
Lava flows rarely kill people because…
- they move slowly enough for people to get out of their way
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
What is a good example of violent eruptions
- The eruption of Washington’s Mount St. Helens
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
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
What does VEI stand for
Volcanic explosiveness index
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
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.)
