Physical Geography: Living with Tectonic Hazards

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Physical Geography: Living with Tectonic Hazards by Mind Map: Physical Geography: Living with Tectonic Hazards

1. Tectonic Plates

1.1. Can be either

1.1.1. Oceanic Crust

1.1.2. Continental Crust

1.2. Always moving

1.2.1. Why? Convection currents 1. Convection currents move within the mantle, causing it to expand, rise and spread out beneath the plates 2. Plates are dragged along and move away from each other 3. Hot mantle material cools slightly and sink, pulling the plates along 4. Sinking mantle material reheats as it nears the core 5. Whole process repeats Slab-pull force Thought to be main driving force for plate movement Dense, sinking oceanic plate at subduction zones pulls rest of the plate behind it Sinking/Subducting of plates drives downward-moving portion of convection currents Mantle material (away from where the plates subduct) drives the rising portion of convection currents

1.2.2. Move a few centimetres a year Noticeable after centuries Movements have altered distribution of land masses over hundreds of millions of years

2. Rock types

2.1. Sedimentary

2.1.1. Formed from multiple layers of sediments

2.2. Igneous

2.2.1. Formed when molten rocks cool and solidify

2.3. Metamorphic

2.3.1. Formed when rocks are changed by high temperatures or pressure within the crust

3. Earth's Internal Structure

3.1. Crust

3.1.1. Outermost layer of the earth

3.1.2. Occupies less than 1% of earth's volume

3.1.3. Few km to <70 km thick

3.1.4. Oceanic crust beneath the oceans 5-8 km thick Consists mainly of basalt heavy and dense rock formed from magma which has cooled quickly

3.1.5. Continental crust beneath earth's continental land masses/continents shallow seas close to continents 35 - 70 km thick Consists of lighter rock eg. Granite

3.2. Lithosphere

3.2.1. Rigid and Brittle

3.2.2. Consists of upper mantle and the overlying crust

3.2.3. Floats on softer asthenosphere

3.3. Mantle

3.3.1. Lies above the core

3.3.2. Mostly solid rock that flows under high temperature and pressure

3.3.3. Occupies 80% of earth's volume

3.3.4. 2,900 km thick

3.3.5. Temperature: 800°C-3,000°C

3.3.6. Two layers: Upper mantle Part of the lithosphere Lower mantle

3.3.7. Consists of Asthenosphere Weak sphere High temperatures and pressure Causes rocks to melt and be deformed easily

3.4. Core

3.4.1. Centre of the earth

3.4.2. Mostly composed of Iron Nickel

3.4.3. ~3,500 km thick

3.4.4. Temperature: 3,000°C - 5,000°C

3.4.5. Separated into: Outer core Liquid Inner core Solid Extreme pressure exerted on it by surrounding layers

4. Tectonic Hazards

4.1. Caused by plate movements when continental crusts and ocean floor move

4.2. Mainly concentrated near coastlines of Pacific Ocean

5. Plate boundaries

5.1. Most of the tectonic hazards occur here

5.2. Plates move at different speeds, in different directions

5.3. Divergent plate boundaries

5.3.1. Plates move away from each other

5.3.2. 1. Magma moves towards the surface

5.3.3. 2, Cools, and forms new oceanic crust along these boundaries

5.3.4. Oceanic-oceanic plate divergence Sea-floor spreading Magma rises from mantle 2. Magma cools and solidifies 3. New sea floor is formed between plates as they move apart Forms mid-oceanic ridge Example Mid-Atlantic ridge (middle of Atlantic ocean)

5.3.5. Continental-continental plate divergence Rift Valleys 1. Plates diverge or move apart 2. Plates are stretched 3. Fractures are formed on the continental crust 4. Linear depression (rift valley) is formed as the crust continues to be pulled apart, and as the land between the plates sink Example East African Rift Valley System

5.3.6. Examples: Southern boundaries of Australian plate Southern and eastern boundaries of Pacific plate

5.4. Convergent plate boundaries

5.4.1. Plates move towards each other and become Faulted Folded Occasionally subducted

5.4.2. Examples: Along the north of the Pacific Plate and the North American Plate Between the Philippine Plate and the Eurasian Plate

5.4.3. Oceanic-oceanic plate convergence 1. Two oceanic plates converge and collide 2. Denser plate subducts under the less dense plate (at the Subduction Zone) 3. Oceanic trench, a depression in the sea floor, forms at the zone 4.1 Subducting plate causes mantle material above it to melt, forming magma 4.2 Magma rises through the crust to form volcanoes, and eventually a chain of volcanic islands will form Example: Mariana Trench and the Mariana Islands

5.4.4. Continental-continental plate convergence 1. Two continental plates converge and collide 2. Both resist subduction as the plates are too thick and buoyant 3. Plates break and slide along fractures in the crust 4. Layers of rock on upper part of crust are compressed together, and fold upwards or sideways 5. Fold mountains are created Example: The Himalayas

5.4.5. Oceanic-Continental plate convergence 1. Oceanic plate converges with Continental plate 2. Denser oceanic plate subducts under less dense continental plate 3.1 Oceanic trench is formed at the subduction zone 3.2 Fold mountains are formed on the continental plate 3.3 Active volcanoes may also form, if magma below the crust rises to the surface (caused by sinking plate) 3.4 Earthquakes may occur on the continental plate Example: Sunda Trench

5.5. Transform plate boundaries

5.5.1. 1. Plates slide/move past each other

5.5.2. 2.1 Transform fault forms

5.5.3. 2.2 Tremendous stress (built up during process) is eventually released commonly in the form of earthquakes

5.5.4. Example: San Andreas Fault Between Pacific Plate and the North American Plate In 1906, an earthquake occurred in San Fransisco, Southern California North Anatolian Fault Between Southern section of Eurasian Plate and the Anatolian Plate A major earthquake has occurred every 10 years on avg in the last 70 years

5.6. Areas of deformation and active earthquake fractures (present within some plates)

5.6.1. Examples African Plate Parts are moving in different directions High chance of intense earthquake and volcanic avtivity

6. Fold Mountains

6.1. Layers of rocks compressed and folded

6.1.1. Consists of Folded rock layer Upfold: Anticline Downfold: Syncline 1. Increasing compressional force on one limb of a fold 2. Rocks may buckle 3. Fracture forms 4. Limb may move forward to ride over the other limb

6.2. How is it formed?

6.2.1. 1. Convergent plates move toward each other and collide

6.2.2. 2. Resultant compressional force creates immense pressure

6.2.3. 3. Layers of rocks undergo folding Folding Layers of rocks buckle and fold Involves compression of rock layers into wave-like structures (folds)

6.3. Locations

6.3.1. Convergent plate boundaries

6.3.2. Younger fold mountains are found along the active plate boundaries

6.4. Examples:

6.4.1. The Andes

6.4.2. The Himalayas Span across southern Asia Formed from collision of northward-drifting Indian Plate and Eurasian Plate

6.4.3. The Rocky Mountains In North America Formed from almost complete subduction of Juan de Fuca Plate beneath North American Plate

6.4.4. The Appalachian Mountains In U.S.A.

6.4.5. The Ural Mountains In Russia Federation

7. Rift Valleys and Block Mountains

7.1. 1. Divergent plate boundaries pull apart

7.2. 2. A 'fault' arises

7.2.1. Fracture in the rocks

7.2.2. Rocks are misplaced

7.3. 3. Tensional forces from (these) movements results in faulting

7.3.1. Parts of the crusts being fractured

7.4. 4. Sections of crusts extend along fault lines

7.5. 5. Tensional forces cause:

7.5.1. 5.1.1. Central block of land to subside between a pair of parallel faults 5.1.2. Rift valley is formed Valley with steep sides

7.5.2. 5.2.1. Land masses surrounding a block of land to subside 5.1.3 Block mountain is formed between a pair of parallel faults Block of land with steep slopes left standing higher than surrounding land

7.6. Locations

7.6.1. May be formed in isolation

7.6.2. May be formed in the same areas Examples: The Basin The Range Province of North America

7.6.3. Divergent plate boundaries Rift Valleys Examples: Block Mountains Examples:

8. Volcanoes

8.1. Landform formed by magma ejected from mantle onto the surface

8.1.1. Magma Molten rock found below the surface Builds up within crust to form a magma chamber Magma chamber

8.2. Locations

8.2.1. Divergent plate boundaries

8.2.2. Convergent plate boundaries

8.2.3. Places where tectonic plates are diverging Examples Atlantic Oceon East Africa Close correlation between location of plate boundaries and distribution of major active volcanoes

8.2.4. Pacific Ring of Fire Most active volcanic eruptions occurs Large number of eruptions and earthquakes occur Along the boundaries of several converging plates Pacific Plate Nazca Plate Philippine Plate Australia Plate Eurasian Plate

8.3. How is it formed?

8.3.1. 1. Mantle material melts at subduction zones, forming magma

8.3.2. 2. Magma rises (less dense than surrounding rock)

8.3.3. 3. Accumulates in magma chamber

8.3.4. 4. Pressure builds up

8.3.5. 5. Magma forces its way onto the surface through vents Vents Openings in the surface with a pipe leading into the magma chamber Vulcanicity Upward movement of magma both into the crust and onto the surface

8.3.6. 6. Magma (Lava) is ejected onto the surface

8.3.7. 7. Lava builds up around vent to form a volcano

8.4. Types of volcanoes

8.4.1. Stratovolcanoes Characteristics Forms from successive eruptions of lava and pyroclasts High volcano Slightly concave profile How is it formed? 1. As more magma seeps into the magma chamber, the amount of pressure in it builds up 2. Volcanic eruption occurs 3. Pyroclasts are released when Stratovolcano erupts 4. New eruption of lava covers pyroclasts and builds up volcano 5. Lava builds up around the vent, solidifying to form a small volcanic cone *Vent may become blocked during formation of volcano, forcing magma to find a new exit to the surface. **Summit of the volcano may be blown off during explosive eruption. Examples Mount Pinatubo Mount Mayon Mount Merapi

8.4.2. Shield Volcanoes Characteristics Gentle sloping sides Broad summit Base of volcanoes increases in size as lava accumulates Locations Formed where low-silica lava has been ejected Common near divergent plate boundaries Example Mount Washington

8.5. Lava

8.5.1. Low-silica lava Low viscosity Less explosive volcanic eruptions Allows gases to escape easily Flows more easily through the vent before reaching the surface Outer layer of cooling lava forms a thin crust once on the surface

8.5.2. High-silica lava High viscosity More explosive volcanic eruptions Traps gases more easily

8.6. Types of volcanic activity

8.6.1. Active Currently erupting Expected to erupt in the near future

8.6.2. Dormant Currently inactive May erupt in the future

8.6.3. Extinct Without current seismic activity No geological evidence of eruptions for the past thousands of years

8.7. Risks of living near volcanic areas

8.7.1. Massive destruction by volcanic materials Volcanic materials caused by eruptions can lead to widespread damage of property Pyroclasts Lava Landslides May occur due to structural collapse of volcano cone during eruption Range from a few rock fragments from volcano to several hundreds of cubic kilometres Have the potential to obstruct the flow of rivers, causing

8.7.2. Pollution Ash particles ejected during eruptions can disrupt human activities over large distances from the volcano Thick plumes of ash may eventually settle on the ground Fine ash particles can be carried by wind over thousands of km Example Eruptions may release harmful gases Carbon dioxide Sulfur dioxide Hydrogen Carbon monoxide

8.8. Benefits of living near volcanic areas

8.8.1. Fertile soil Lava and ash from eruptions break down to from fertile volcanic soils Richest soils on earth Very favourable to agriculture Rich in minerals Example Java, Indonesia Bali, Indonesia

8.8.2. Precious stones and minerals Volcanic rocks can be rich in precious stones and minerals Can only be extracted from volcanic areas after millions of years Example Diamond

8.8.3. Tourism Volcanic areas offer a variety of activities for tourists to engage in Hike Camp Enjoy scenery Learn more about the areas Example Ruins of Pompeii, Italy

8.8.4. Geothermal energy Derived from heat in the crust Groundwater touches hot rocks beneath the surface Heats up and erupts as hot water or steam Can be harnessed to Example Iceland

9. Earthquakes

9.1. Vibration in the crust caused by the sudden release of stored energy in the rocks found along fault lines

9.2. Occur when there is plate movement along plate boundaries

9.2.1. Plate movement causes slow build-up of stress on rocks (on either side of the fault)

9.2.2. Rocks cannot withstand increasing stress

9.2.3. Rocks suddenly slide many metres

9.2.4. Earthquake occurs

9.3. Key words

9.3.1. Seismic waves Energy is released in the form of these waves Radiate out from focus

9.3.2. Focus A point of sudden energy

9.3.3. Epicentre Point on surface directly above focus

9.3.4. Aftershocks Small earthquakes caused by stress from ground within the crust (after an earthquake) that occur along the fault line Series of aftershocks may occur for several months after earthquake Some may be as powerful as original earthquake Example

9.4. Types of earthquakes

9.4.1. Deep-focus earthquake 70-700 km below surface Smaller impact on land Vibrations/Seismic waves

9.4.2. Shallow-focus earthquake Upper 70 km of crust Greater impact on land

9.5. Extent of damage

9.5.1. Different amounts of energy are released Amount of energy released = Magnitude of earthquake

9.5.2. Richter Scale Used to measure magnitude of earthquakes Impact becomes 10 times greater (in magnitude) for each increasing magnitude

9.5.3. Factors Population Density Number of people living in the affected area More people = More damage and casualties (vice versa) Level of preparedness Amount of preparation taken by authorities and citizens Better trained --> More manageable earthquake Examples Distance from the epicentre Area closer to epicentre --> Severe damage Example Time of occurance Time of day which an earthquake occurs Affects chances of survival in an earthquake Example Type of soil 1. Loose and unconsolidated sediments 2. Amplified seismic waves 3. Greater damage when earthquake occurs Example

9.6. Locations

9.6.1. Divergent plate boundaries

9.6.2. Convergent plate boundaries More frequent occurrences More stress builds up when one plate subducts under another Examples Earthquake in Tohoku, Japan Earthquake in Indian Ocea

9.6.3. Transform plate boundaries

9.6.4. Pacific Ring of Fire Three quarters of earthquakes that occur each year are found along here

9.6.5. Some earthquakes may occur away from plate boundaries Example Earthquake in Sichuan, China

9.7. Measuring

9.7.1. Seismograph Records seismic waves released by earthquakes

9.7.2. Global Positioning System (GPS) Measures location shift (as a result of an earthquake) Location shift is closely related to magnitude of an earthquake

9.8. Risks

9.8.1. Tsunamis One of the most damaging hazards Unusually large sea wave Can travel long distances Cause widespread destruction at coastal areas when it sweeps inland Possible reasons of formation Movement of sea floor during a large earthquake at subduction zones Explosive underwater volcanic eruption Landslide above sea level How is it formed? Seismic energy from an offshore earthquake forces out a mass of seawater Waves may start at a height of less than 1 m, with wave lengths of 100-150 km at speeds of 800 km/h and may pass undetected Greater friction slows the waves and forces them to increase height upon reaching shallow water Waves could be travelling at 30-50 km/h and may reach heights of around 15 m at the point of impact Occasionally, the sea recedes from the coast before advancing offshore. Example Tsunami in Indian Ocean

9.8.2. Landslides Shaking of ground during earthquakes can weaken slopes of hills and mountains Rapid downslope movements of soil, rock and vegetation debris from a slope Can range from several metres to several kilometres in both length and width Mudlslides May occur if there is heavy rainfall Often occurs in Indonesia and the Philippines Example Landslide on Mount Huascaran, Peru

9.8.3. Disruption of services Can potentially affect a large area Can disrupt the supply of Can affect communication services Example Earthquake in Kobe, Japan

9.8.4. Destruction of properties Can cause widespread destruction to many homes People may be homeless after the disaster Example Earthquake in Haiti

9.8.5. Destruction of infrastructure May cause cracks to form on infrastructure Roads Bridges May disrupt transportation Unsafe to use the damaged roads Example

9.8.6. Loss of lives Earthquakes and the associated hazards often threaten lives of those who live near earthquake zones Example Earthquake in Northern Pakistan

9.8.7. Geography Earthquakes can change landscapes Maps become inaccurate

9.9. Example

9.9.1. Strongest earthquake ever recorded In Valdivia, Chile 1906 9.5 on Richter scale