Tectonics Flashcards
Where do the majority of tectonic hazards occur and what % of earthquakes are found in the Ring of Fire in the Pacific Ocean?
At plate boundaries, 70%
Why do most tectonic hazards take place at plate boundaries?
Plate boundaries can slide past or crash into each other so tectonic strain builds up between plates and when pressure exceeds friction, the rock fractures and huge amounts of energy released in form of seismic waves
What is ground-shaking in an earthquake?
Brittle crust either side of the fracture rebounding
What is the order of explosivity of different boundary types?
O-O –> O-C –> C-C
least explosive –> most explosive
What makes volcanoes more explosive at certain plate boundaries?
High silica content so high viscosity so high gas content
What are the case studies for an effusive, explosive, and very explosive volcano and what type of magma did each have?
Effusive: Iceland 2010 - basaltic
Explosive: Mt. St. Helen’s 2010 - andesitic
Very explosive: Mt. Pinatubo 1991 - rhyoltic
What was the VEI of the Icelandic eruption in 2010?
VEI 4
What was the VEI of the Mt. Pinatubo eruption in 1991?
VEI 6
Which type of plate movement has a shallow focal depth and why is this dangerous?
Conservative - seismic energy has less distance over which it can dissipate so higher magnitude earthquake due to tectonic strain
What is the case study for conservative plate movement, what was its focal depth, and what was its magnitude?
Haiti 2010, 13km, 7.0 magnitude
Which plates were involved in the 2010 Chile earthquake?
Nazca and South American plates
What was the magnitude of the 2010 Chile earthquake and how many people were killed?
8.8 magnitude, 525 people killed
What type of plate movement was involved during the 2010 Chile earthquake and why did this make it so dangerous?
Convergent, shallow focal depth so greater intensity ground-shaking
Where and how do intra-plate earthquakes occur?
Occur along ancient faults, slip easily to accommodate regional strain so forces exerted at all sides and strain on ancient fault produced which releases energy in form of seismic waves
Why are intra-plate earthquakes sometimes more dangerous than ones at plate boundaries?
Usually low level of preparedness as they are considered as low risk due to not being located at a plate boundary
What is the case study for an intra-plate earthquake?
Gujarat, India 2001
What was the magnitude and how many people were killed as a result of the 2001 Gujarat, India earthquake?
7.7 magnitude, 20,000 people killed
What is a volcanic hotspot?
Area of mantle
How can a volcanic hotspot create a volcanic island chain?
Heat rises as stationary thermal plume, high heat and low pressure at base of lithosphere melts rock so molten rock rises through cracks and erupts on Earth’s surface, tectonic plates move over stationary hotspot and oceanic volcanoes can cool, forming volcanic island chain
What is an example of a volcanic island chain?
Hawaii
How hot is the inner core and what is this caused by (convection currents)?
6000°C, caused by radioactive decay
What causes the mantle to become less dense and rise into the lithosphere (convection currents)?
Heat from the inner core radiates into the outer core and then the mantle
Which direction is the mantle forced in when it becomes less dense and rises into the lithosphere (convection currents)?
Sideways
What happens to the mantle after it is forced sideways in the lithosphere (convection currents)?
Cools down and becomes more dense so sinks back down to the core to form a convection current