A Level CIE Geography: Hazardous Environments

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hazard

a threat that could injure people and damage the built environment. an earthquake in an unpopulated area is a physical event and only becomes a hazard when people put themselves in danger by moving into the area. natural hazards occur where humans interact w/ the physical world and their severity and frequency depends on human activity

disaster

a hazard that causes so much damage and injury that recovery without help is impossible

risk

the exposure of people to a hazard event

vulnerability

the degree to which conditions make a population more likely to experience a hazard event which they do not expect, cope with or recover from

resilience

how well a population recovers from a disaster

five classifications of hazards

• cause

  • technological/geological e.g. earhquakes and volcanic eruptions

  • geomorphological/processes acting on land surface e.g. mass movenets

  • atmospheric/meteorological e.g. tropical cyclones and tornadoes

• magnitude, scale, size (some have own scales)

• freq. of occurence

• length of warning time - rapid onset hazards are much mroe dangerous than slow onset

• spatial distribution

what are most earthquakes and where do they occur

tectonic. on all types of plate boundary, hotspots away from plate boundaries and at fault lines

how are seismic waves formed

when two plates try to move but become stuck against each other, stress builds up and eventually the plates break free along a fault causing a sudden release of pressure and releasing a tremendous amount of energy = seismic/shock waves from the point of movement/focus/origin of earthquake.

epicentre

point on earths surface immediately above the focus, where seismic waves are strongest but the greatest damage doesn’t always occur there

where do most earthquake foci occur

narrow zones along plate boundaries but their effects extend far beyond the plate boundary

4 types of seismic zone

• destructive/convergent plate margins have shallow, intermediat4e and deep earthquakes inclined along benioff zone on subducting plate where slab pull occurs

• collision boundaries of two converging continental plates e.g. eurasian and indian - himalayas

• conservative plate margins where faults e.g. san andreas in california have earthquakes but no volcanic activity e.g. na and pacific plates = great friction builds and catch = powerful earthquakes from shallow focus

• constructive plate margins at mid-ocean ridges wheere ridges push (slab push) occurs. lithosphere too weak and thin for lot of stress to build up so large earthquakes dont occur. usually shallow focus and occur w volcanic avtivity

when are earthquakes non tectonic

caused by human activity putting too much stress on faults. 7.9 mag earthquake in sichuan china 2008 killed 70k ppl was linked to construction of a resevoir which added very heavy weight of water to surface

volcano

results from build up of molten material emitted onto surfaace thru opening or fissure in crust

active volcano =

has erupted in the last 80 years (in historic time)

dormant volcanoes

inactive but may become active again in the future

extinct volcanoes

not erupt again

seismographs

record the seismic energy waves that earthquakes send out.

primary (P) waves

travel fastest and arrive at a place first

secondary (S) waves

after p waves.

surface waves

slowest waves, travel along earth’s surface.

regular large amplitude waves (surface)

long waves w large amplitude and cause most of the damage as they shake ground most violently.

richter scale

measures the total amount of energy released/magnitude of an earthquake

no. earthquakes increase as magnitude..

decreases

mercalli scale

12 points, measures intensity (amt of physical damage of earthquake)

isoseismal lines can be drawn how

using mercalli scale measurements

how deep can the focus of an earthquake be

up to 700km, below that the rocks are so hot they bend rather than break

why are deep focus earthquakes less destructive than shallow focus ones

because the thickness of rocks above the focus absorbs the shockwave. its strength reduces with increased distance from the focus

how are buildings destroyed

by shaking and by ground tilting/subsiding as shock wave passes

what 3 secondary hazards result from shaking of the ground

• landslides

• soil liquefaction

• tsunamis

landslides example

• april 2015 shallow 7.9 mag earthquake struck nepal w/ epicentre 80km nw of kathmandu.

• climbers at south base camp on mt everest abt 200km away reported that after ground shook = massive fall of rocks, snow and ice down the mountain causing 19 deaths in camp

• frost shattered rocks broken free when shaken and gravity moved them quickly down the steep slopes.

• landslides blocked roads delaying arrival of aid

soil liquefaction

occurs when shaking of ground makes weak or unconsolidated rocks act as a liquid and flow, leading to sinking and destruction of buildings. occurs when groundwater is near surface and soft sediment like sand mixes w/ water

tsunamis

high, long period waves in the ocean resuslting from sudden displacement of sea bed along a fault.

tsunamis formation

• in open ocean tsunami wave crests are small and wave lengths very long making them difficult to monitor

• when wave crests reach shallow water at the coast they slow and rise dramatically in height

• the waves then retreat pulling water back out to sea before returning to hit coast w tremendous force

• height can exceed 30 m and can flood coasts thousnads of km from focus

why do coastal areas near earthquake epicenters have little or no warning

tsunami travels very rapidly. e.g. tsunami generated by large quake off west coast of sumatra dec 2004 reached aceh province in few mins after so ppl fleeing from quake were caught in flood that surged inland

flood following earhtquake

• more damage, injury and death occur

• if shock wave causes dam wall to collapse/large landslide to fall into lake = sudden flooding down valley

why are there outbreaks of disease after natuarl disassters

surivvors forced to live in camps w insanitary conditions

why cant magnitude be plotted on normal linear scale scattergraph

magnitude can be plotted on linear scale but the greaet range of deaths makes it immpossibel to plot them on a normal linear scale scattergraph. on graph log scale has cycles each of which given a value ten times size of adjacent loewr cycle

what graph paper must be used

semi-lograithmic graph paper (log-normal graph paper) with one linear scale and other logarithmic mmust be used

features of semilog graph

on graph log scale has cycles each of which given a value ten times size of adjacent lower cycle. start of cycles can be 0.1, 1, 10, 100, 1000, 10000 and so on

do scales need to extend to values below lowest values indata on graph

no

where does scattergraph start

100 because not enough cycles on paper to show values below 100. first cycle subdivided 100, 200, 300

primary hazards of volcanic emissions

• gases

• liquids

• solids

what gases contribute to hazardous volcanic emissions 4

• water vapour

• carbon dioxide

• sulphur dioxide

• hydrogensulphide

how does water vapour contribute to volcanic primary hazards

consitutes up to 80% of the gases emitted and, after conversion to rain, is responsible for dangerous mudflows and lahars.

how does sulphur dioxide contribute to volcanic primary hazards

can corrode aircraft

how does hydrogen sulphide contribute to volcanic primary hazards

toxic

primary gaseous hazards - volcanic emissions

• nuee ardente

how are nuee ardente’s formed 3 + example

• long period of inactivity and highly viscous magma

• solid plug grows in vent of volcano

• highly gas-charged lava eventually explodes sideways out of weakness in flank of volcano

• e.g. st pierre from mt pelee on martinique in caribbean 1902: 2/30000 ppl survived.

4 features of nuee ardentes

• very hot, incandescent cloud 

• composed of gas and tiny fragments of solid material

• moves very rapidly down slope, keeping contact w it

• temp can reach 1000 celsius

type of liquid primary volcanic emissions

• lava

2 types of lava

• pahoehoe

• runny basalts - aa lava

what is lava

both the liquid that flows out of the crater of the volcano and the rock it forms when solidified.

how is lava formed

it originates from magma, molten rock beneath the surface, which rises from a magma chamber beneath the volcano through a vent to reach the surface.

what are the most dangerous lava flows

runny basalts

features of runny basalts

• occur at constructive plate margins and oceanic hot spots

• can move 50km an hour

• anything in path is rapidly covered

fastest basalt lava

aa type

aa lava features 4

• formed when lots of lava erupts quickly

• thick up to 10m deep

• surface breaks into rough clinkers as it moves

• steep sloping front moves forward as a unit with sudden dangerous surges of speed, destroying anything it touches

pahoehoe lava features 5

• less than 2m thick

• forms when low volumes are ejected more slowly

• solidifies while moving, its smooth surface has curved flow lines giving it a rope-like appearance. 

• flows in individual lobes, moving around obstacles, setting flammable objects on fire

• less viscous than aa so flows slowly and further

type of solid primary volcanic emissions

pyroclastic material

pryoclasstic material

solid particles that reach ground in pyroclastic falls (airbrone = tephra).

how is pyroclastic material formed 

some is shattered remains of plug that solidified in the vent after previous eruption. other pieces form when molten lava solidifies in air.

how is volcanic solid material categorized

by shape and size

types of pyroclstic materials

• ashes

• cinders

• lapilli

• volcanic blocks

• volcanic bombs

what are ashes 

smallest are less than 4mm in diameter 

what are cinders

4-5mm in diameter

lapili

pebble-sized

volcanic blocks

large angular fragments resulting from the shattering of solid lava during an eruption

volcanic bombs

rounded because they form as molten lava cools while spinning through air

are ejections of pyroclastic materials dangerous

• yes, usually hot, heavy and ash can cause roofs to collapse and damage crops, machinery, electronics and people’s lungs.

• heavier particles e.g. bombs usually fall to ground within 3km of vent but the lighter particles can rise high into atmosphere where they can damage aircraft engines.

• e.g. enormous ash cloud emitted by evjafjallajokull in 2010 drifted over Europe from iceland and disrupted flights for more than a week more than 100k flights were cancelled costing airlines almost 2.5 bill

pryoclastic flows

when lava domes collapse, hot, dry, rock fragments and gases move rapidly away from the vent down slopes and valleys by gravity. they kill almost half the pppl who die as a result of volcanic eruptions.

why r pryoclastic flows highly destructive

high density and fast travel speed 80km/hr - 100km/hr, long distances covered and intense heat 200C to 700C.

danger of pyroclastic flows

• density lowest at top of cloud and greatest in base flow so densest part containing bouldersized fragments moves in contact w ground and destroys everything with which it makes contact.

• above the base flow hot gases keep the ash fragments buoyant. heat sets nearby buildings, forests, and crops on fire and people and animals on the edges of flows die from breathing in hot gases.

• wide areas are buried by hot pyroclastic debris up to 200 thick that often welds together.

• if loose, it can provide material for equally hazardous lahars to occur if water is added to deposit.

• nuees ardentes described earlier are categorised as a special type of pyroclastic flow being characterised by their incandescent ashes that glow in the dark

types of volcano

• cinder cones

• shield volcanoes

• stratovolcanoes

• lava domes

cinder cone features

• form when blobs of gas-charged lava are thrown into air and break into fragments

• e.g. lava butte in oregon, during growth it blocked and diverted deschutes river

shield volcanoes features

• formed of basic lava, containing less than 50% silica

• its fluid flows long distances and solidifies slowly

• issues from fissures, it forms extensive \

• result when theres a central vent

• enormous with very wide bases and gentle slopes of about 5*

• e.g. deccan in india

where shield volcanoes form

• along constructive plate margins e.g. in iceland, built up above sea level by layer upon layer of lava

  • e.g. mauna loa in the haiwaiian islands largest acctive volcano in world on hotspot from ocean flor to summit rises to 9km greater than mt everest height above sea lvl

hotspot 

plume of molten material from mantle ejected at surface far from a plate boundary 

where do stratovolcanoes form

form at convergent/destructive plate boundaries where magma gains added silica as it rises thru continental rocks

stratovolcanoes features

• as lavais intermediate between acidic and basic, its more viscous than that of a shield volcano, resulting in steeper sides, which usually steepen towards summit giving a concave slope overeall

• base is narrower than that of shield volcano

• parasitic cones form on sides of volcanoes when main vent becomes blocked and magma finds other way out

why are stratovolcanoes particularly dangerous

• they have long dormant periods so ppl not always convinced that they should heed warnings to evacuate

eruption of stratovolcanoes

• during dormanyc thick plug of solidified magma builds up in vent and as magma has high viscocity a considerable amt of pressure builds up to unblock vent usually culminating in explosion which shatters plug into pyroclastic fragments followed by outpourings of lava.

lava dome features

• relatively small domes

• steep sides

• rounded tops

• form on slopes of or in craters of stratovolcanoes

• composed of silicic lava w/ 60%+ silica which is too viscous to flow far so soldifies quickly formiong thick crust

• domes swell as they grow from within

• verry explosive eruptions when they collapse

• mt pelee in martiniquye developed lava dome before 1902 eruption

7 types of volcanic eruptions

• icelandic

• hawaiian

• strombolian

• vulcanian

• vesuvian

• plinean

• pelean

icelandic eruption

fluid basalts issue quietly from fissures at mid-ocean ridges

hawaiian eruption

fluid basalts issue from vents in volcanoes. gases escape easily and quietly with occasaional spurts of gases from lava lakes causing lava fountains

strombolian eruption

less fluid lava and gases escape with moderate explosions in whihc lava bombs are ejected. known as ‘lighthouse of mediterranean’ bc very frequent activity

vulcanian eruption

eruptions are more violent bc more viscous lava solidifies more quickly and traps gases. ashes and cinders emitted when pressure released. dark ash-laden clouds rise to form caulifloewr shape

vesuvian eruption

viscous magma gains high gas content during long periods of inactivity and deep plug forms which can only be blwon off after considerable pressure has built up. vioelnt eruption sends wide dark ash cloud into stratosphere. ash falls over wide area. ad 79 eruption of vesuvius buried town of pompeii under 25m of tephra

plinean eruption

a very violent explosion of gas, ash and pumic = narrower cloud that extends into stratosphere. high ash cloud from mt pinatubos 1991 eruption circulated world several times in stratosphere so temp global cooling 0.5c

pelean eruption

highly viscous magma and long period of inactivity cause an explosion out of weakness in side of volcano with a nuee ardente falling down slope

volcanic explosivity index (VEI)

• scale from 0-8 logarithmic like richter

• vei 4 and up send mats into stratosphere and capable of global cooling

• largest eruption = tambora, indonesia 1815 vei 7

2 secondary volcanic hazards

• lahars

• volcanic landslides

lahars

volcanic mudlfows form when water mixes w loose pyroclastic material with particle sizes varying from small debris to boulders, forming flows resembling wet concrete down slopes of volcanoes and into valleys beyond them.so

4 source of water in lahars

• intense rainfall acoompanying eruption

• glacier melt

• snow melt

• dam faailure

lahar features

• dense and viscous

• flow very fast uip to 75km/h

• more volcanic material = faster flow = more destructive

• common on steep slopes of stratovolcanoes where downward pull of gravity strong but can occur on shield volcanoes e.g. iceland.

• quickly increase in size as they gain more water and erode more material to carry but die out as move away from volcano

volcanic landslides

• masses of rock and soil moving downslope under gravity cna be dry or wet, although drier than lahars. with the addition of water as they flow, they can tarnsform into lahars if htey contain more than 3% fine clay particles

landlsides originate

large slabs of rock but disintegrate into progressively smaller particles as they move downslope.

volcanic landslides features 4

• can be as huge as 100km³ in volume 

• faster than 100km/hr

• can rise over ridges, as occured when north face of mt st. helens collapsed durin 1980s eruption

• resulting landslide crossed 500m high ridge 5km from crater

when do volcanic landslides result

when magma forces its way to the surface and pushes outwards, causing the rock to break or over-steepen and collapse by gravity down the high, steep sides of stratovolcano. they can also be triggered by large earthquakes beneath  a volcano 

what do volcanic landslides trigger

volcanic explosions by removing lid on the gases and rising magma. they bury valleys and after coming to rest, cause lahars as water drains down-valley form them.

• fastest flow of mt st helens lahars was five hoursa ft4er landslide stopped moving and they travelled 55km further than the landslide

• do not stop moving btu change gradually into a lahar can travel more than 100km and are most hazardous

• when landlsides block tributary valleys they impound lakes which can suddenly break through natural dam and cause further lahars e..g kyushu island japan 1792 resulted in tsunami causing 15000