Tectonic processes and Hazards (EQ 1) Flashcards
Causes of Earthquakes
Earthquakes are primarily caused by the movement of Earth’s tectonic plates and the stress that accumulates along faults, volcanic activity and human activities can also contribute to seismic events.
Causes of Volcanic eruptions
Volcanic eruptions are primarily caused by the movement of magma from the Earth’s mantle to the surface due to pressure build up and geological processes associated with tectonics plates.
Causes of Tsunami’s
Tsunamis are primarily caused by the sudden displacement of a large volume of water, often resulting from underwater earthquakes, volcanic eruptions and landslides, the displacement of water sets off a series of powerful waves in both directions that can travel across entire ocean basins, posing significant threats to coastal areas.
Global Distribution patterns of volcanos and earthquakes
Plate Boundaries: The majority of volcanoes are located along tectonic plate boundaries
Anomalies being from intraplate earthquakes and hotspots
What are Convergent Plate Boundaries
Convergent boundaries occur where tectonic plates move toward each other. This motion results in the collision or subduction of plates, leading to intense geological activity.
What are Divergent Plate Boundaries
Divergent boundaries occur where tectonic plates move away from each other. This motion is typically associated with the upwelling of material from the mantle, creating new crust.
What are Conservative Plate Boundaries
Conservative boundaries occur where tectonic plates slide past each other horizontally. This lateral motion results in strike-slip faulting and seismic activity
Distribution of Convergent Plate Boundaries
Commonly located around the edges of ocean basins there are 3 main types being : Ocean-ocean convergence , ocean-continent convergence and continent-continent convergence
Distribution of Divergent Plate Boundaries
Divergent plate boundaries are often found along mid-ocean ridges, which are long underwater mountain ranges that traverse the ocean basins
Causes of volcanoes associated with hot spots from mantle plumes
When one of the Earth’s plates moves over an unusually hot part of the Earth’s mantle. These hot areas are usually relatively stationary and result in large amounts of magma rising up, piercing a hole in the plate to form a volcano
7 Factors that influence the severity of an earthquake on a place
- Tectonics and the global distribution of earthquakes
- earthquake magnitude and depth
- Population density
- Building and structural vulnerability
- Extent of earthquake awareness
- levels of development
- Governance
How is the force of an earthquake measured
On the Richter scale
How does the depth of the earthquake cause greater loss of property and life
Shallow earthquakes that occur close to the surface tend to result in a greater intensity of surface shaking and often cause the greatest loss of life and damage to property
How do shallow earthquakes occur
Destructive margins where the subducting plate descends at a slight angle thereby creating stresses close to the surface.
What is liquefaction and how does it exacerbate impacts of earthquakes
Some materials are vulnerable to becoming jelly-like when shaken, commonly associated with clays and silts. causing foundations of certain areas to become unstable and slopes become vulnerable to mass movement
Explain why hotspots occur
An area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.
Evidence for continental drift
- Jigsaw fit
- Geological fit
- Tectonic fit
- Glacial deposits
- Fossil evidence
What is isostatic change
- layers of ice weigh down plates during ice ages
- when the ice melts, the land rises again
What is slab pull
Theory of plate tectonics which occurs at subduction zones. The thinner denser oceanic crust subducts below the thicker less dense continental crust. Convection currents move this crust, causing the subduction to become deeper. Gravity causes the subducted crust to be pulled down further and at a faster rate than the convection current
What is ridge push
- Due to convection currents in the mantle, hot magma rises and at divergent boundaries along mid ocean ridges, the magma erupts through and cools, forming dense volcanoes. gravity acts on the volcanoes and pushes them down and away form the ridge causing the plates to move apart
What is a tsunami
A series of waves, generated by a sudden displacement of water in the ocean.
Why were the tsunamis from the Indian ocean in 2004 so devastating
-there is no early warning system for the Indian ocean unlike the pacific basin due to the infrequency of tsunamis here, unprepared.
-Earthquake its self was a 9.0 on the Richter scale
Island chains were low lying
-Densely populated
- Extremely poor countries were affected such as Indonesia and Sri Lanka
How did the world respond to the 2004 disaster
Over £700 million had been committed for the recovery by foreign governments. £300 million in the first seven days
Emergency supplies being flown in
How can the tsunami hazard be reduced?
-One is behavioural and relates to forecasting, warning and evacuation. Such an approach also encompasses land use management, public awareness and education.
- The other is structural and involves the building of structures to physically withstand tsunami and protect coastlines.
Tsunami mitigation in Japan
- Dwelling houses to high ground
- Evacuation roads
- flood proof buildings
- Sea walls up to 10 metres high
- Offshore breakwaters
Explain the global distribution of earthquakes
The global distribution of earthquakes is predominantly associated with tectonic plate boundaries, where the movement and interaction of Earth’s plates generate stress along faults and release it in the form of seismic events. However, intraplate earthquakes, hot spots, and human-induced seismicity can also contribute to earthquake activity around the world.
Explain the causes of intra-plate earthquakes (4 marks)
The reactivation of ancient fault lines within a tectonic plate. These fault lines formed millions of years ago and since have become locked. Over time, stress accumulates along the faults due to movement of the earth’s interior, eventually leading to fault slippage and an intra plate earthquake.
What is palaeomagnetism and sea floor spreading?
- Mid ocean ridges are formed when hot magma from the asthenosphere rises and forms new oceanic crust
- The new crust pushes the tectonic plates apart in a process called sea floor spreading
- Magnetic materials in the magma align themselves in the direction of the earths magnetic field, which cool and solidify once becoming crust
- Alternating magnetic stripes in the sea floor indicated that crust has formed at different times of polarity.
- Age of rocks mirrored either side of the mid ocean ridge
