Chapter 2: Plate Tectonics and Physical Hazards

Earth Structure
- Inner Core - Solid, High Temperature, 90% Iron, 1300 km thick
- Outer Core - Liquid, similar to inner core, 2000 km thick, density of 10.7 g/cm3
- Mantle - Solid, iron & magnesium-rich silicate rocks, 3000 km thick, density of 4.5 g/cm3
-Lithosphere
- Outer rind of the Earth - made up of tectonic plates
- Asthenosphere - Below lithosphere - Hot layer of weak rocks
- Crust - Outer rock layer of Earth, density of 2.8 g/cm3 - Moho – the boundary between Earth’s crust and mantle, marks the base of the continental crust, separates lighter crustal rocks from the more dense mantle
- Isostacy (buoyancy) is the reason why there’s a difference in elevation between continental and oceanic crusts
- Plate tectonics describes the movements of Earth’s plate (moves up to 11 cm/year)

Hazards and Plate Boundaries
- Most of tectonic actions, like earthquakes and volcanoes, occur near boundaries of the plates
- Divergent boundaries: plates pulled away from each other by the sinking of lithosphere at oceanic trenches - If the plates are continental plates, once pulled apart they will form a continental rift zone, which can develop into a new ocean. Spreading continues allowing basaltic magma to push to the surface.
- Convergent boundaries: plates moving towards each other
- Subduction zone: when one or both plates are oceanic and the denser ones slides down into the asthenosphere.
- Collision zone: In cases, where neither is dense enough to be subducted, it will collide into a continental material, creating mountain ranges.
- Transform boundaries: two plates sliding pass each other, can cause major earthquakes
- Seafloor spreading: when oceanic crusts well up, spread apart, and form trenches.
- Hotspots: chains of volcanoes within individual plates, lying above a