Geography Paper 3: Tectonic Hazards

Drivers of plate movements

Convection currents, slab pull, and ridge push

Slab pull

The force that pulls plates along as they sink at a subduction zone. 

Ridge push

The force that pushes plates apart at mid-ocean ridges where new crust is formed

Convection cell

Cycle of rising and sinking magma caused by heating through radioactive decay of core

Factors affecting type of plate boundary

Plate density and direction of plate movements

Landforms at collision boundaries

Fold mountains (synclines/anticlines), accretionary wedges, and high plateaus

Landforms at subduction boundaries

Composite volcanoes, island arcs, ocean trenches, accretionary wedges

Landforms at divergent boundaries

Mid-ocean ridges, rift valleys, shield volcanoes and fissure volcanoes

Landforms at transform boundaries

Fault lines (and associated uplift/downdrop)

Events at collision boundaries

Low frequency, high magnitude earthquakes

Events at subduction boundaries

Major volcanic eruptions and earthquakes

Events at divergent boundaries

Minor volcanic eruptions and earthquakes

Events at transform boundaries

High frequency, low magnitude earthquakes

Example of convergent boundary

Indo-Australian/Eurasian (Himalayas landform)

Example of subduction boundary (oceanic/oceanic)

North-American/Pacific (Aleutian Islands landform)

Example of subduction boundary (oceanic/continental)

Nazca/South-American (Peru-Chile Trench landform)

Mantle plume

Area of superheated rising magma which spreads and melts crust, creating a hotspotSei

Seismicity

The occurrence and magnitude of earthquakes associated with an area

Earthquake focus

Origin of an earthquake within the Earth

Earthquake epicentre

The point on the Earth’s surface vertically above the origin

P wave

Longitudinal body wave that can travel through solids and liquids - faster wave, causes initial “bump” in an earthquake

S wave

Latitudinal body wave that travels through solids - slower wave, causes shaking in earthquakes and is responsible for most damage

Love wave

Latitudinal (horizontal plane only) surface wave - causes significant damage to building foundations

Rayleigh wave

Elliptical-motion surface waves - contributors to surface fissures and infrastructure damage

Secondary hazards of earthquakes

Landslides, liquefaction, tsunamis, gas leaks, flooding

Scales for earthquake magnitude

Modified Mercalli Scale (best for responders) and Richter Scale (best for seismologists)

Earthquake prediction methods

Seismic Gap Theory, stress redistribution modelling, fault tiltmeters, and monitoring unusual animal behaviour

Earthquake preparation methods

Seismic dampeners, counterweights, deep foundations, retrofitted superstructures, insurance policies, real-time warnings

Earthquake response methods

Emergency services, emergency shelters, stockpiling, international aid

Earthquake recovery methods

Earthquake-proofing, hazard-mapping and public awareness programmes

Conditions for earthquake-caused tsunami

At least 7.0 on Richter, vertical seabed displacement, shallow focus

Steps in tsunami formation

Initiation (seabed movement), split (distant/local tsunamis), amplification (steepening), and runup (onshore height above sea level)

Extrusive volcanic features

Volcanoes, geysers, and mud-pools

Intrusive volcanic features

Sills, dykes, batholiths

Characteristics of basaltic lava

Basic, low viscosity, low silica content, hotter (1200^oC), runs further and faster, and found at divergent boundaries/hotspots

Characteristics of andesitic lava

Acidic, high viscosity, high silica content, cooler (800^oC), short and slow flow, and found at destructive boundaries

Sill

Horizontal band of igneous rock

Dyke

Vertical band of igneous rock

Batholith

Large underground dome, possibly and old magma chamber

Scale for volcanic eruption magnitude

Volcanic Explosivity Index (logarithmic scale)

Example of basaltic explosion type

Icelandic eruption

Example of andesitic explosion type

Vesuvian eruption

Example of rhyolitic explosion type

Plinian eruption

Primary volcanic hazards

Lava flows, pyroclastic flows, ash/tephra fall, and volcanic gas emissions

Secondary volcanic hazards

Lahars, volcanic landslides, tsunamis