Hazards- Concepts/plate tectonics

Hazards- Concepts/plate tectonics

1. Constructive

   • Two plates move apart- magma will rise
     • Ocean ridges- diverging plates underwater create this. Volcanoes erupt in mid-Atlantic ridges, go above sea. E.g., Mid-Atlantic Ridge in Iceland.
     • Rift Valley- as plates move apart, parallel faults drop down to form Rift Valleys. E.g., East African Rift system- series of riot valleys that stretches from Mozambique to Red Sea.

2. Destructive Subductive

   • Oceanic crust subducts under continental crust due to density.
     • Deep Ocean Trench- oceanic subducts under continental crust. Form deep-sea trench. E.g., Peru-chill trench in Pacific Ocean.
     • Island Arc- oceanic subducts under oceanic forming Deep Sea Trench which triggers volcanic eruptions and underwater Island Arcs forms which are chains of volcanoes. E.g., Marniqua Islands.

3. Destructive Collision

   • Plates move together (continental +continental/ oceanic +oceanic).
     • Fold mountains- when continental crust converge. E.g., Himalayas where created this way.

4. Conservative

   • Plates slide past each other. Does not expose mantle. E.g., San Andreas fault in California.

5. Magma Plumes

   • Vertical column of magma rises up mantle. Crust moves above it. Volcanoes form in crust that is above magma plume. As crust moves, chain of volcanoes form. E.g., chain of islands in Hawaii formed by this.

6. Disaster Risk Management Cycle

   • Pre-disaster- before hazard. Mitigation/prevention- warning systems. Risk assessment- potential harm.
     • Section 1- response- short-term. Service response, response to damage.
       • Section 2- post-disaster- long-term. Recovery- rebuilding the place.
         • Section 3- mitigation- acting to reduce scale of next disaster- land-use zoning, hazard-resistant buildings and infrastructure.
           • Section 4- preparedness- community education and resilience including how to act before, during and after disaster, warning and evacuation technology and systems.

7. Park Model of disaster response

   • Section 1- pre-disaster- preparation.
     • Section 2- Disaster.
       • Section 3- Relief- aid- services, rescue teams- Qaulity of life goes down.
         • Section 4- Rehabilitation- recovery- state of normality. Lasts few days to weeks.
           • Section 5- Reconstruction- rebuilding- takes weeks to even years.

8. Impacts of hazards

   • HIC- short relief. Short rehabilitation. Quality of life= high.
   • NEE- shirt relief. Long rehabilitation. Quality of life= low.
   • LIC- long relief. Long rehabilitation. Quality of life= low.

9. Lithosphere

   • Rigid top part of mantle and crust together.

10. Asthenosphere

    • Layer above lithosphere.

11. Convection currents

    • Circular movements of semi-molten rock (magma). Creates drag on base of tectonic plates, causing them to move. Cause earthquakes and eruptions.

12. Slab Pull

    • Oceanic crust is forced under becoming less dense and slowly rises. Sinking of the plate edge pulls the crust of the plate to the boundary. Can cause Volcano chains to appear.

13. Ridge Push (gravitational sliding)

    • Constructive margins. Magma rises to surface forming crust. Heats surrounding rocks, which expands above the surface of surrounding crust, forming a slope. Crust cools and gets denser. Gravity causes denser rock to move down slope, away from plate margin. Puts pressure on tectonic plates, causing them to move apart. Causes ocean ridges and rift valleys. Can cause earthquakes many kilometres away from ridge.

14. Sea-floor spreading

    • When the sea floor spreads apart along divergent boundaries and forms the mid-ocean ridge (constructive margins). New oceanic crust is formed through volcanic activity than and then gradually moves away from ridge.