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Hazardous Earth Flashcards

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1
Q

define a hazard

A

a threat (natural or human) that has the potential to cause loss of life, injury, property damage, socio-economic disruption or environmental degradation.

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2
Q

what two ways is the structure of the earth defined as?

A

Concentric structure defined in two ways - chemical composition and mechanical properties

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3
Q

what components are present in the chemical composition structure?

A

crust:
solid outer layer, silica-rich, 30-40 km thick in continental areas less dense, made of granite granite
oceanic crust denser but thinner (5-8 km) and made of basalt
Mantle:
Denser rock underneath crust, extending down 2900 km to core-mantle boundary (CMB), richer in iron and magnesium
Chemical changes occur in mantle transition zone (MTZ) from 410-660 km

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4
Q

what componants are present in the mechanical property system?

A

Lithosphere - cool, brittle outer shell, comprising crust and uppermost, rigid part of mantle. Broken into lithospheric plates (tectonic plates). Deeper into earth temperatures increase. At 1300 degrees mechanical properties change from elastic to plastic, making the base of the lithosphere. Most have continental and oceanic crust.
Asthenosphere - solid mantle rock, but hotter and under greater pressure so more ductile. Important role in tectonics allowing rigid plates to slide over it
Outer core - molten iron, convects, generating magnetic field
Inner core - iron but solid due to greater pressure despite being 5400 degrees

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5
Q

what are the role of convection currents and why are they important for geography?

A

Mantle convection fundamental to tectonics providing a mechanism by which earth cools over time through the formation and movement of plates at the surface
It was thought plates were moved by currents caused by heating but geologists now believe it is driven by cooling from above

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6
Q

how do convection currents work?

A

at subduction zones, slabs of cold oceanic crust become dense enough to sink into mantle (downwelling) - causes lithosphere to be stretched and thinned elsewhere (constructive plate margins), reducing pressure on underlying mantle rock causing it to upwell in response
upwelling thought to occur in thin column plumes rising from the core-mantle boundary - linked to subducted slabs reaching the bottom of the mantle

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7
Q

what is the disadvantage of convection currents

A

complex pattern and also not all understood yet

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8
Q

what did the theory of continental drift suggest?

A

1915 Wegener published theory of continental drift the idea that rather than being fixed the continents were moving
He proposed the 250Ma continents were joined into supercontinent (Pangaea) which broke up

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9
Q

what is the evidence for the continental drift theory?

A

Jigsaw fit - coastlines are complimentary
Geological fit - similar mountain chains/rock outcrops on either side of oceans
Ancient glaciations - glacial deposits and striations formed 300Ma suggest a single ice sheet once covered a massive land mass close to south pole
Fossil records - fossils found on either side of the oceans but nowhere else e.g. Mesosaurus in SA and Africa

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10
Q

what is the theory of sea-floor spreading?

A

1931 Holmes - ocean floor is continuously recycled, sinking in some areas and replaced elsewhere
1950s Hess proposed sea-floor spreading as a mechanism

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11
Q

how does paleomagnetism provide evidence for sea-floor spreading?

A

Iron-rich minerals in lava align with Earth’s magnetic field
Shows every few 100,000 years magnetic field reverses polarity
Vine and Matthews 1963 - rocks either side of the Carlsberg mid-ocean ridge mirrored each other in striped pattern of normal and reversed polarity - new ocean floor produced by volcanic activity at ridges and spreads as plates diverge

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12
Q

how does the age of sea rocks provide evidence for sea-floor spreading?

A

Gradually increases with distance each side of a mid-ocean ridge
Discovered in late 1960s due to deep-sea drilling project which dated rocks using fossils

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13
Q

why do theories change over time and what is the most recent theory?

A

With new evidence, ideas became more sophisticated and new theory of plate tectonics was created.

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14
Q

what is the global pattern of plates and plate boundaries?

A

1940s detailed maps of seismic activity showed most earthquakes concentrated in narrow bands with large aseismic areas in between. Volcanoes had a similar pattern - idea rigid lithosphere broken into plates
7 large and several smaller lithospheric plates - move over asthenosphere few cm per year

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15
Q

what is a convergent (collision) boundary?

A

plates move towards each other (no subduction)

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16
Q

what is a convergent (destructive) boundary?

A

plates move towards each other (denser plate subducts)

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17
Q

what is conservative (transform) boundary?

A

plates move alongside each other

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18
Q

what is a divergent (constructive) plate boundary?

A

plates move away from each other

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19
Q

what are the characteristics of divergent boundaries?

A

Sea floor spreading - plates pulled apart, lithosphere stretches and thins reducing pressure on asthenospheric mantle - upwells and partially melts - magma rises to form new crust
Mid ocean ridges (MORs) form 60,000km long chain of submarine volcanic mountains, warm, thin lithosphere over areas of upwelling
Transform faults - offset MORs every 50-500km, generating shallow earthquakes. Slow spreading MORs have central rift valley, formed where crust moves up along vertical faults as it spreads from ridge axis
Ridge push - MORs have higher elevation than surrounding ocean floor - plates slide down either side due to gravity pushing the rest of the plate away from ridge

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20
Q

what are the characteristics of C-O convergent boundaries?

A

Denser oceanic plate subducts beneath continental plate due to gravitational force, rigidity of plate allows it to bend elastically under stress causing deep ocean trenches
Sea-floor sediments scraped off oceanic plate create and accretionary wedge - adds new material to continent so grows laterally. Continental lithosphere folded and faulted produces fold and thrust mountains
Subducting oceanic lithosphere becomes more dense as it falls due to higher temperatures, pressure. Greater gravitational mass and increases capacity to pull - slap-pull (cold dense slab of oceanic lithosphere subducts into mantle pulling rest of plate with it)
Release of water from oceanic lithosphere into overlying wedge of mantle, lowering melting point and causing partial melting
Less dense magma rises through overlying continental lithosphere forming volcanoes
Earthquakes common due to faulting in subducting slab - Wadati-Benioff zone (sloping plane of earthquake foci) goes from trench down to 700 km

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21
Q

what are the characteristics of O-O boundaries?

A

Similar features and processes
Denser plate (older and cooler) subducts
Magma generation forms island arcs (chain of volcanic islands formed on overriding plate)

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22
Q

what are the characteristics of C-C boundaries?

A

Ocean has already been subducted and who continents collide
Continental lithosphere not sense enough to sink into mantle so no volcanoes or subduction
Folded and faulted into mountain chains (violent earthquakes) and intense pressure (metamorphism) e.g. Himalayas

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23
Q

what are the characteristics of conservative plate boundaries?

A

Jerky and sporadic movement
Frictional forces lock sections of boundary together along faults, building up strain energy.
When slips occur energy is released as earthquakes - no volcanic activity
E.g. San Andreas fault (Pacific-NA plate)

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24
Q

what are the factors that affect different types of volcano?

A

Eruptions (explosivity, materials ejected and size/shape of landforms) affected by: composition of magma/lava (high silica content are more viscous than mafic)
Convergent usually produce silicic magmas, divergent boundaries and hot spots mafic
Dissolved gas in magma affects the force of eruptions

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25
Q

what are the characteristics of explosive eruptions?

A

Trapped gas bubbles burst violently when magma reaches surface - vent and top of cone often shattered
Rhyolitic and andesitic
Silica, high viscosity
700-1000 degrees
Lava, gases (water vapour, CO2, N, SO2), pyroclastic material (tephra - dust, ash, lava bombs)
Sporadic - long periods with no activity
Steep-sided composite volcanoes - stratovolcanoes, calderas
Usually convergent, but can happen at divergent/hot spot
Mount ontake, Japan 2014

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26
Q

what are the characteristics of effusive eruptions?

A

Gas bubbles escape easily, lava flows freely with limited explosive force
Basaltic
Mafic, low viscosity
>1000 degrees
Lava, gases (water vapour, CO2, N, SO2)
Regular - eruption can continue for months/years
Shield volcanoes with gentle slopes - lava plateaux
Divergent and hot spots
Geldingadalur, Iceland 2021

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27
Q

why do eruptions happen even though they are not at a plate boundary?

A

Results from mantle plumes reaching the base of the lithosphere
Causes partial melting and an area of volcanic activity - hotspot
Plume is stationary when the plate moves over it, leading to a chain of volcanoes which become extinct when transported away.
Associated with basaltic lava, shield volcanoes and flood basalts

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28
Q

what are fissures?

A

linear volcanic vents through which lava erupts effusively (cause flood basalts and lava plateaux)

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29
Q

why are volcanoes difficult to classify?

A

Dominant lava chemistry and eruption style of single volcanoes can change over time and larger volcano have smaller cones on their flanks

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30
Q

what are the characteristics of composite volcanoes?

A

alternating layers of tephra and viscous lava pile up near the vent, forming conical shape with steep sides. No more than 10 km diameter but can exceed 3000 m in height, 30 degrees slope

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31
Q

what are the characteristics of shield volcanoes?

A

layers of low-viscosity lava flow far from the vent, giving a broad, rounded shape with gentle slopes, 5 degrees, varies in size largest 100 km wide

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32
Q

what are the characteristics of super volcanoes?

A

volcano that has erupted >1000 km2 of material in a single event, highly explosive, eject so much magma that the chamber is emptied and volcano collapses on itself forming a caldera

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33
Q

what is the VEI?

A

Volcanic explosivity index

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34
Q

what does the VEI measure?

A

magnitude of volcanic eruptions to compare them

35
Q

how does the VEI measure magnitude?

A

volume of material ejected, eruption plume height and qualitative descriptions to assign a value from 1-8
Each increase is a 10 fold increase in explosivity
8 = supervolcano

36
Q

what are some examples of different types of eruption styles?

A

Icelandic eruptions - VEI 0 - effusions of basaltic lava flow from fissures - lava plateaux
Hawaiian eruptions - VEI 0-1 - flow from single vent and flank fissures to form shield
Strombolian eruptions - VEI 1-2 - mildly explosive but frequent eruptions of gas/tephra
Plinian eruptions - VEI 4-8 - extremely explosive - immense eruption clouds and eject huge volumes of pyroclastic materials

37
Q

how do earthquakes cause hazards?

A

Lithosphere is constantly under stress from tectonic forces - causes build up of strain energy
Stress overcomes strength of rock causing faults
Some intraplate earthquakes occur due to faults

38
Q

what are the characteristics of a geysir?

A

fountain of hot and cold water as well as steam that are ejected from the ground at great speed. shoot up into the sky up to 100m.

39
Q

how are geysirs formed?

A

water underground is heated by magma that is nearby and the water becomes hot. superheated water - temperature can be >100 degrees as it is under pressure. theory that a chamber of water being heated by rocks. linked to the surface by a narrow vent. pass the boiling point of water and becomes steam which then explodes and forces water up the vent.

40
Q

what are the characteristics of hot springs?

A

Hot water from underground comes to the surface. temperature needs to be above human body temp.

41
Q

how are hot springs formed?

A

wherever groundwater is heated by magma underground.

42
Q

what are the characteristics of fumaroles/solfatara?

A

vents giving off steam and volcanic gases

43
Q

how are fumaroles/solfataras formed?

A

occur wherever superheated water reaches the surface and gases come out of solution and bubble off.

44
Q

what are the characteristics of a batholith?

A

what is left of a magma chamber that has cooled and formed granite that is hard to erode. other rock around is easier to erode and crust level has dropped so the igneous rock is left sticking up out the ground. only eroded by huge glaciers.

45
Q

how are batholiths formed?

A

magma forced into crustal rocks - intruded. happens when fold mountains are formed causing rock to melt and over time builds up in mass beneath surface and then cools and solidifies.

46
Q

what are the characteristics of a dyke?

A

igneous rock - granite/basalt/etc. looks like sea wall. harder rock that has been exposed as surrounding weaker rocks have been weathered and eroded. as land surface drops harder rock left behind.

47
Q

how are dykes formed?

A

discordant as magma gets in to rock and stick up from layers. cuts across rock vertically.

48
Q

what are the characteristics of sill?

A

huge and small features. magma has intruded into rock and follows the lateral pattern of the rock solidifying in layers. surrounding rock gets worn down and harder resistant rock is left behind.

49
Q

how is sill formed?

A

concordant - follow pattern of rock.
whin sills formed.

50
Q

what are the characteristics of lava flows?

A

Hawaii July 2015 20km flow. 800m in one day.
Basic (basaltic) lava is free-flowing and can run for large distances. acidic lavas such as rhyolite are thick and pasty so do not flow easily

51
Q

what are the impacts of lava flows?

A

dependent on type of lava. everything in the path of lava will be burned, bulldozed or buried. destroy infrastructure, property, crops. lava flows rarely cause injuries or fatalities.

52
Q

what are the characteristics of pyroclastic flows?

A

Pompeii AD79 M. Vesuvius
combination of hot gases (500 degrees+), ash and rock fragments travelling at high speed (100km/hr).

53
Q

what are the impacts of pyroclastic flows?

A

follow contours of the ground and destroy everything in their path. The inhalation of such hot and poisonous gas and ash causes instant death.

54
Q

what are the characteristics of ash and tephra fall?

A

Eyjafjallajokull volcano April 2010 cancelled 100,000 flights.
any material ejected from a volcano into the air. Ranges in size from very fine ash to volcanic bomb (>6cm across). includes lighter debris such as pumice.

55
Q

what are the impacts of ash and tephra fall?

A

very hazardous, burying farms in layers of ash and destroying crops. Transport can be disrupted both on the ground and in the air. buildings collapse due to weight of ash and people with respiratory diseases can struggle to breathe.

56
Q

what are the characteristics of volcanic gases?

A

including CO, CO2 and SO2
eruptions emit a wide range of toxic gases.

57
Q

what are the impacts of volcanic gases?

A

deadly and silent threat to humans, when SO2 combines in atmospheric water, acid rain is produced. enhances weathering and damages crops and pollutes surface water and soils.

58
Q

what are the characteristics of lahars?

A

1984 Nevado del Ruiz, Columbian town of Armero overwhelmed. 23,000 died.
type of mud flow with the consistency of wet concrete. snow and ice on a volcano summit melt during an eruption and flow rapidly down the cone. Rock fragments large and small, as well as ash and soil, are mixed together. can travel 50km/h.

59
Q

what are the impacts of lahars?

A

everything in their path is either destroyed or buried under thick layers of debris. after rainfall hazards can remain.

60
Q

what are the characteristics of floods (Jokulhlaups)

A

Iceland, several active volcanoes lie under th Vatnajokull ice field.
volcanic eruptions beneath an ice field or glacier cause rapid melting. vast quantities of water accumulate until they find an exist. causes a torrent of water.

61
Q

what are the impacts of jokulhlaups?

A

devastating floods

62
Q

what are the characteristics of volcanic landslides?

A

mt St Helens - biggest landslide in recorded history at the time
as magma is forced up and the ground bulges, dome collapses and causes landslides. also may happen as ash lands on slopes and collapses as too heavy forcing a slide.

63
Q

what are the impacts of volcanic landslides?

A

localised damage

64
Q

what are the characteristics of tsunamis?

A

Krakatoa 1883 is believed to have drowned 36,000 people.
Characteristics - violent eruption of some island volcanoes can cause massive displacement of ocean water and tsunami waves capable of travelling up to 600 km/h. In deep water they have a height that is less than 1m and a long wavelength of 200 km. approaching the shore, waves increase in height and when they break transfer vast amounts of energy and water along the shore and inland.

65
Q

what are the impacts of tsunamis?

A

devastating flooding and loss of life and infrastructure

66
Q

what are the characteristics of shallow earthquakes?

A

0-70 km focal depth
All plate boundaries and intraplate locations
Evidence lithosphere is divided into plates
Stronger ground haking at surface
Gound shaking concentrated into smaller area
E.g. Kashmir, Pakistan 23 km, M 7.5, deaths >87,000

67
Q

what are the characteristics of deep earthquakes?

A

70-700 km focal depth
Destructive plate boundary
Evidence for existence and nature of subduction
Weaker ground shaking as seismic waves decreased with distance from focus
Shaking over wide areas because waves spread out as they move away from focus
Hindu Kush, Afghanistan 212 km, M 7.5, deaths 399

68
Q

define magnitude

A

amount of energy an earthquake releases - each only has one

69
Q

how is magnitude measured?

A

Richter scale - energy released using maximum amplitude of seismic waves recorded on seismogram
Moment magnitude scale - additional parameters (size of fault rupture and rock strength) to increase accuracy - main scale used, each increase = 10-fold increase in shaking and a 32-fold increase in energy release, however, logarithmic scale which makes it difficult for the public to understand - prevents preparedness

70
Q

define intensity and what does it depend on?

A

amount of ground shaking in a specific location depends on:
Magnitude
Distance from epicentre and focus
Rock and soil characteristics
Resistance of buildings/infrastructure to ground shaking

71
Q

how is intensity measured?

A

Modified Mercalli intensity scale
12-point scale based on qualitative descriptions of shaking felt and observed impact on built environment
Intensity of single quake observed in many locations can be plotted on map using isolines
Depends on human perception, vary and reduce accuracy - more useful than magnitude in assessing impact

72
Q

what are the main effects of earthquakes on landforms and landscapes?

A

Earthquakes occur only faults, (brittle fractures in lithosphere), rock on either side is displaced, sometimes by metres at a time - dramatic and widespread effects
Lithosphere stretched at divergent, faults dipping towards each other develop parallel to the margin. Land between blocks either side are elevated - creating a rift valley e.g. East African Rift
Steep slope formed where fault breaks the surface forms an escarpment - help form fold and thrust mountains

73
Q

when does a earthquake become a hazard?

A

when they affect people

74
Q

what are the primary hazards of an earthquake

A

ground shaking and displacement - moves vertically and horizontally - shaking intensity depends on magnitude, distance from epicentre and focus and geology

75
Q

what are secondary hazards caused by?

A

ground shaking

76
Q

what are the secondary hazards of an earthquake?

A

Liquefaction - when violently shaken, unconsolidated deposits (sand/slit on floodplain) with high water content lose mechanical strength and become fluid
Landslides and avalanches - shaking can trigger slope failure and mass movement, the 2015 Nepal earthquake caused >21,000 landslides and avalanches on Mount Everest
Tsunamis - giant waves from large, sudden displacement of sea water, usually underwater earthquakes which cause seabed uplift (less often than volcanoes/landslides). Deep water wavelengths often >100 km, low wave height <1 m. when reaching shallow water/land they slow and increase in height. When 1st wave hits shore causes sea level to drop (drawdown), immediately behind is wave crest, travel several km inland.
Flooding - indirectL trigger tsunamis, destabilising/destroying dams, destroying/lowering protective levees, causing landslides which dam rivers to create ‘quake lakes’ (dams can later collapse)

77
Q

how and why has the risk of natural disasters changed over time?

A

Earthquakes cause significantly more deaths than volcanoes
Number of geophysical events has not changed over time
The number of people living in hazardous areas has increased
Number of geophysical disasters (earthquake, volcano or mass movement affecting >100 people) has increased over past 50 years with 30 per year today compared to half in 1960s
Human activity may have increased secondary hazards

78
Q

what is the disaster risk equation?

A

Degree of risk posed by a hazard is related to its magnitude, how often it occurs and level of vulnerability of the people living there
Risk (R)= Frequency of or magnitude of hazard (H) x level of vulnerability (v)/capacity of the population to cope and adapt (c)
R = HV/C

79
Q

what do the different components of the disaster risk equation mean?

A

Generally, greater magnitude, less frequently it occurs
High-magnitude, rare events release large amounts of energy and have the greatest impact on human populations
Vulnerability is concerned with the ability of a community to withstand exposure to a hazard. Vulnerability increases risk

80
Q

how might deterministic predictions reduce risks of earthquakes?

A

Stating exactly when and where an earthquake of a certain magnitude will occur is not possible, but research is ongoing

81
Q

how might probabilistic forecasting reduce risks of earthquakes?

A

Uses seismic monitoring, historical records and fieldwork (e.g. GPS to measure ground deformation around fault zones) to estimate earthquake likelihood
Can be used to improve adaptations - prioritising vulnerable locations for investment
Developments of GPS-A - unmanned vehicles called wave gliders float at sea for months, detecting sea floor motion to help understand tsunamis

82
Q

how might aseismic design reduce the risks of earthquakes?

A

Major role in future mitigation with new techniques e.g. eco-friendly ductile cementitious composite (EDCC)
Success depends on effective designs as well as adaptation to local cultural, economic and institutional factors that influence compliance with building codes
Affordable, low-tech solutions can be used if funds are limited, 2007-2012 smart shelter foundation created 15 earthquake-resistant schools in Nepal which all survived the 2015 quake

83
Q

what is the Park model (disaster-response curve)

A

Response = sequence of stages
Disaster response curve (park model)
Adjusted to fit and allow comparison between individual events

Geography (8 decks)

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