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Y1,S1-Natural Hazards > Y1,S1 - Natural Hazards > Flashcards

Y1,S1 - Natural Hazards Flashcards

1
Q

What is magma generated by? (HINT- 3 factors)

A

1.Increased temperature
2.Decreased Pressure
3.Adding Volatile elements

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2
Q

What is the upper mantle made of?

A

Peridotite

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3
Q

What happens to the temperature of the mantle as its depth increases?

A

Temeprature increases

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4
Q

What happens when the pressure or temperature of peridotite (upper mantle) is altered, causing it to pass the geotherm?

A

Lithospheric mantle is created

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5
Q

Where is water trapped in the upper oceanic crust?

A

Crystals

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6
Q

What happens to temeprature and pressure as depth of the mantle increase?

A

They both increase

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7
Q

Why does subducting oceanic crust alter the liquedous conditions of the upper mantle?

A

Water is released as crystals, it was previously stored in,melt

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8
Q

What does increasing the liquedous conditions of magma result in?

A

Magma ascension (volcano formation) over long time scales (millions of years)

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9
Q

In most places does magma rise to the surface due to an increase in temperature or decrease in pressure, as it reaches the geotherm?

A

Decrease in pressure

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10
Q

Give an example of where magma is reaching the geotherm due to a decompression?

A

East African rift valley

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11
Q

What causes hotspot volcanism?

A

Upwelling of magma (mantle plume) from the mantle-outercore boundary, despite being a solid it moves up towards the surface over tens/millions of years, driven by byouyancy

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12
Q

what is magma?

A

Multiphase mixture of melt (liquids), crystals (solids) and gas (bubbles)

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13
Q

Why do volatiles in magma drive the eruption?

A

Because they from bubbles which accelerate the magma upward

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14
Q

What is magma mixing?

A

Hot magma replenishment which disrupts the chamber

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15
Q

Why deoes magama mixing cause eruptions?

A

The increased temperature of magma replenishment mixes with the cool magma sitting in the reservoir, destablising the chamber. Pressure and volume changes as crystals and vesicles mix, causeing acceleration.

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16
Q

Ultramafic lava contains…

A

Peridotite
Low SiO2 content

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17
Q

As crystal content in lava increases, what else increases (3 factors) ?

A

Silica content
Na and K content

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18
Q

As silica content increases does temperature increase or decrease?

A

decrease

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19
Q

Name the 4 different magma compositions from highest SiO2 content to lowest…

A

1.Felsic
2.Intermediate
3.Mafic
4.Ultramafic

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20
Q

What main factor (mineral) changes the viscosity of magma?

A

Silica content

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21
Q

Name the 5 types of magma in order from highest to lowest viscosity?

A

1.Rhyolite
2.Andecite
3.Dacite
4.Basalt
5.Komatite

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22
Q

Describe basaltic volcanoes?

A

-Typical temp. 1000-1200C
-SiO2 45-52 wt% [mafic]
-High conc. of Fe, Mg, Ca
-Low conc. of Na, K, Si & H2O
-Typically contains olivine, plagioclase (Ca-rich) & pyroxene
-Low viscocity (flows easily)
-E.g. Kileaua , Mt Etna & Bardabunga

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23
Q

Decribe Andesitic volcanoes?

A

-Typical temp. 800-900C
-SiO2 52-63 wt% [Iintermediate]
-lower conc. of Fe, Mg, Ca than basalt
-higher conc. of Na, K, Si & H2O than basalt
-Typically contains amphibole, plagioclase & pyroxene
-E.g. Tungurahua, Fuego & Soufiere hills

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24
Q

Describe dacitic volcanoes?

A

-Typical temp. 800-900C
-SiO2 63-70 wt% [Iintermediate]
-Often crystal rich
-Viscuous - eruptions can be highly explosive
-Typically contains amphibole, plagioclase (Na-rich), mica & pyroxene
-E.g. Mount St Helens & Pinatubo

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25
Q

Describe rhyolitic volcanoes?

A

-Typical temp. 600-800C
-SiO2 more than 70 wt% [Iintermediate]
-low conc. of Fe, Mg, Ca
-high conc. of Na, K, Si & H2O
-Viscuous - often highly explosive
-Typically contains amphibole, plagioclase (Na-rich), mica & quartz
-E.g. Yellowstone, Chaiten & Nemrut Dagh

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26
Q

What are polygenetic volcanoes?

A

-Magma erupted repeated from same plumbing system
-E.g Stratovolcanoes, caldera volcanoes, sheild volcanoes

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27
Q

What are monogenetic volcanoes?

A

-Magma plumbing sytem only used once
-E.g Lava shields, Volcanic fissures, Scoria cones

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28
Q

What are stratovolcanoes characterised by?

A

-Steep conical shape
-Small summit crater
-Layers of lava and tephra

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29
Q

What are sheild volcanoes characterised by?

A

-Low profile
-Summit crater, rift zones
-Layers of fluid lava flows

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30
Q

What are caldera volcanoes characterised by?

A

-Large cauldron-like crater
-Formed by evacuation of large magma chamber

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31
Q

List the eruption classifications following the general trend of increasing intensity, explosivity and duration…

A

1.Hawaiin
2.Strombolian
3.Vulcanian
4.Plinian

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32
Q

What are some generic direct volcanic hazards?

A

Generic:
-Caldera and sector collapse
-Volcanic gases
-Earthquakes

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33
Q

What are some effusive direct volcanic hazards?

A

Effusive:
-Lava fountains and flows

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34
Q

What are some explosive direct volcanic hazards?

A

Explosive:
-Tephra fall
-Pyroclastic density currents
-Ballistic projectiles

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35
Q

What are some indirect volcanic hazards?

A

-Lahars, mudflows, debris flows
-Debris avalanches
-Landslides
-Acid rain and pollution (SO2 ->H2SO4)
Tsunamis

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36
Q

What affects the speed of lava at effusive eruptions?

A

1.Type of lava erupted and its viscocity
2.Steepness of the ground over which it travels
3.Whether the lava flows as a broad sheet, through a confined channel or down a lava tube
4.Rate of lava production at the vent

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37
Q

Describe and list affects of low viscocity lava flows at effusive eruptions:

A

-Can be sustained for days-weeks or even longer
-Mostly a threat to infrastructure
-Can dam rivers
-Long recovery period

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38
Q

List 3 examples of effusive eruptions:

A

-Hawaii (low viscosity lava)
-Mt Etna (high viscosity lava)
-Soufiere hills (high viscocity lava)

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39
Q

Describe and list affects of high viscosity lava flows at effusive eruptions:

A

-High viscociyy lavas extrude more slowly, but can be highly charged with volatiles

Lava domes:
-Advance slowly
-Shorter flows
-Eruptions continue for months to decades
-Long recovery periods

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40
Q

Describe and list affects of explosive eruptions:

A

-Range of eruption types up to Pinion
-Sustained for hours to days
-Plumes up to ~10-50km high
-Ejecta may extend hundreds of km from vent (fallout)
-Generates tephra fall and pyroclastic density currents
-Can lead to many indirect hazards

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41
Q

What are pyroclasts?

A

-Volcanic rock fragments produced by explosive eruptions
-collectively known as pyroclastic deposits or tephra

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42
Q

What is the general size of ash (type of tephra) ?

A

<2mm

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43
Q

What is the general size of lapilli (type of tephra) ?

A

2-64mm

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44
Q

What is the general size of blocks and bombs (type of tephra) ?

A

> 64mm

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45
Q

What are accesssory lithics?

A

Wall rock (accidental) fragements that are picked up from the magma, hence foreign particles that travel woth the volcanic ash

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46
Q

What are juvenile particles?

A

Fragmenst/particles that are cooled from the magma itself

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47
Q

Describe tephra fall and its affects?

A

-Particles decrease in size as distance from the vent increases, hence quite well organised
-Thicker deposits closer to the vent (but sometimes a secondary thickening downwind)
-Blankets the landscape beneath the eruptions plume, continuous layer

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48
Q

Describe the hazards caused by tephra fall (proximal to medial) :

A

-10-30cm required to collapse on buildings (less when went due to rainfall)
-Depends on; construction type, roof span, pitch angle, water content
-Roof collapse
-Respiratory problems
-Driving accidents
-Smother or poison vegetation and animals (e.g. flurosis in cattle)

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49
Q

Describe the hazards caused by tephra fall (distal) :

A

Distal ash in the atmosphere has profound impacts for the aviation industry:
-Closes airports
-Closes airspace
-Causes mechanical damage
-Ash is highly abrasive and corrosive

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50
Q

How do isopach maps, map tephra fall deposits?

A

Based on measurments of deposit thickness over a wide area (contours of equal thickness)

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51
Q

How do isopleth maps, map tephra fall deposits?

A

Based on the measurement ofthe maximum average (lithic or pumice) clasts at any location (contours of equla maximum clast size)

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52
Q

What are pyroclastic density currents (pdcs)?

A

Mixtures of hot particles (ash to boulder size) and gas that moved down the flanks at high speeds as density currents

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53
Q

What are the characteristics of pdcs?

A

-Temperatures up to several hundred degrees C
-Velocity of a few tens of m/s, up to 300m/s
-Typically travel several metres from vent but can travel >100km
-Also referered to as pyroclastic flows (concntrated mixture) or pyroclastic surges (dilute mixtures)

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54
Q

Describe how pdcs form from the collapse of an eruption column and its affects:

A

-Unstable eruption column (due to insufficient entrainment air)
-Collapse of material
-Condenses on the ground -> density current
-Can produce radial flows
-Contains mostly pumice and ash

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55
Q

Describe how pdcs form from the collapse of a lava dome and its affects:

A

-Grvitational instability of solid lava dome (due to oversteepening of planks and gap P)
-Collapse and disintegration
-Mixture expands -> density currents
-Produces flows in direction of collapse
-Contains mostly lava blocks and ash

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56
Q

Describe the nature of column collapse pdcs:

A

-Generally formed during short-lived eruptions
-can be highly mobile (increased height that the flows initiate from)
-Can be roduces radially around vent

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57
Q

Describe the nature of dome collapsed pdcs:

A

-Repeated inundation of flanks by pdcs during long-lived eruption
-Up to 30km runouts
-Recover period depends on deposit thickness and climate

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58
Q

What are lahars?

A

A hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and/or river valleys

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59
Q

Describe the characteristics of lahars:

A

-Vary in size and speed, from a few m/s up to several tens of m/s
-Reach rdistal locations, often far removed from volcanoes

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60
Q

how are lahars formed?

A

Mix loose volcanic debris with water on a slope by:
-collapse of water-saturated or ice-covered volcano
-Rapid melting of snow and ice during eruptions
-Eruption through crater lake
-Heavy rainfall on fresh pyroclastic deposits
-Overtopping/failure of impounding lakes

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61
Q

How have we learnt to cope with volcanic eruptions?

A

-Enhanced use of tehnology
-Social media as a critical tool
-Nationwide coordination
-Croos-disciplinary collaboration
-Psychological readiness
-Re-evaluation of hazard zones
-Flexible monitoring strategies

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62
Q

How are short-term hazards monitored?

A

Monitoring data and activity observations

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63
Q

How are long-term hazards monitored?

A

Based on field records, datesand occurences over long-time periods

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63
Q

What is shot-term hazard monitoring used for?

A

-Evacuation orders
-Disaster mitigation
-Crisis Management

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63
Q

What is long-term hazard monitoring used for?

A

Land use planning

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64
Q

What are geological volcanic hazard maps used for?

A

Presenting hazards based on their past occurrence

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65
Q

What are integrated qualitative volcanic hazard maps used for?

A

For simplified communication

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66
Q

What are modelling-based hazard maps?

A

Maps based on the study of a single hazrd using empirical relationships and/or modelling tools employed either deterministically or probabilistically.

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67
Q

What are possible uncertainties associated with modelling-based hazard maps?

A

-Digital elevation models
-Input parameters

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68
Q

What are geophysical signals at volcanoes?

A

-Regional tectonics
-Pathway and recording effects
-Moving fluids
-Movig magma
-Shallow sources
-Edifice instability
-Deep sources of magma

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69
Q

What are different types of volcano monitoring?

A

-Geophysical/deformation monitoring (using tiltmeter and GPS)
-Volcano seismology (using EQ and lahar sensors)
-Acoustic monitoring (Infrasounds which travel thousnads of km can detect volcanic explosions very well, that humans cannot)
-Geodesy (tool used to measure ground deformation and gravity changes cause by magama movement)
-Thermal remote sensing (detects heating up of the surface, which captures surface radiance of the ground prior to an eruption)
-Lightning detection
-Physical volcanology (elemants and minerals found determine stage and type of eruption)

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70
Q

What are the tectonics of South America?

A

-Nazca plate subducting eastwards beneath continental South American plate
-Convergence causes uplift of the Andes
-Subduction causes earthquakes and volcanism

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71
Q

What are the tectonics of Equador (Tungurahua)?

A

-Nazca plate moving Eastward at ~56mm/yr
-Active subduction off west coast of Ecuador
-Intraplate EQs resulting from movement of continental ‘sliers’

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72
Q

At what zone is Tungurahua?

A

Subduction zone

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72
Q

What type of Volcano is Tungurahua?

A

Andesitic Volcano

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73
Q

What are some of the hazards created by Tungurhua?

A

-Pyroclastic density currents
-Tephra fall
-Lahars

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74
Q

How was Tungurhua monitored?

A

-Geophyiscial monitoring networks
-Local observers

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75
Q

What forces are involved in causinf slope instabilities?

A

Driving forces and ressiting forces

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76
Q

What is the driving force in slope instabilities?

A

Gravity

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77
Q

What are the resisting forces involved in slope instabilities?

A

-Strength
-Friction
-Cohesion

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78
Q

What other factors are invoilved in slope instabilities?

A

-Excess loading
-Water( increases loading, reduces cohesion)

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79
Q

Describe soil creep:

A

-Moves slowly downslope, <mm/yr
-Most important in terms of volumes involved
-Creep is enhanced by steep slopes, water in soil, tree fall and bioturbation

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80
Q

What are landslides favoured by?

A

-Rainfall ( pore pressure reduces frictional resistance to sliding)
-Disappearance of vegetation ( roots provides resistance to slope failure
-Ground shaking (EQs)

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81
Q

What does deep seated landslides involve?

A

-Soil
-Bedrock
-Curved failure surface
-Large volume
-Usually after extended periods of rain

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82
Q

What do shallow landslides involve?

A

-Soil ONLY
-Subplanar failure surface
-Small volume
-Usually after intense rain
-Can be induced by creep + freeze/thaw
-No loss of life BUT damage to structures

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83
Q

What is a landslide?

A

Material moving in contact with underlaying surface as cohesive blocks of material with limited internal shearing

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84
Q

What are debris flows/ mud flows?

A

-When material breaks up and moves as a viscuous fluid
-Material is transported mostly by gravity, not water

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85
Q

What is the difference between dry rock avalanches and debris/mud flows?

A

Dry rock avalanches do not involve water whereas the others do

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86
Q

What is required for a debris/mud flow?

A

-Mass transport of poorly compacted material (e.g.soil)
-High pore water content
-Large quantities of fine material (to prevent water escape)

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87
Q

Can landslides turn into debris/mud flows?

A

YES and can transport very large particles (fast-moving dense flurry)

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88
Q

What makes a mudflow?

A

-High clay-silt content
-Common in volcanic terrain (lahars), can happen long after eruption

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89
Q

What are the direct natural causes of mass movement?

A

1.Saturation of water (pore pressure;lubrication) - Change in groundwater table, heay rains and rain following drought)
2.Over steepening of slopes - Erosion by streams, waves and glaciers
3.Freeze and thaw cycles -Over time creep destabilises slopes resulting in sudden failure
-frost shattering on rocky slopes
4.Vegetation -Loss of vegetation by wildfires, wind erosion, drought destabilises slopes
-Plants with shallow roots and large foliage can be destabilised by rain

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90
Q

What are indirect causes of mass movement?

A

-Initiated by other hazard events- EQs, volcanic eruptions
-Initiated by human activity (e.g. deforestation, rainfall caused by climate change)

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91
Q

Is the energy recievd by Earth evenly distributed?

A

NO:
-More solar energy arrives at the equator than poles
-As solar radiation arrives directly at the equator, whereas it arrives on a slant at the poles
-This generates an Equator-pole tempearture gradient

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92
Q

What is the Equator-Pole temperature gradient?

A

-Heat flows from hot towards cold
-This transfer of energy from Equator to Pole generates weather

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93
Q

What drives the diurnal cycle?

A

Rotation of the Earth

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94
Q

What drives the seasonal cycle?

A

Tilt of rotation axis

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95
Q

Describe the single-cell model:

A

-Convection cell
-Hot air (less dense) rises at the Equator, moves towards poles at high altitude, then cools and sinks at the Pole
-Circulation completed by cold air moving towards Equator near surface
-This is partly correct, but is too simplified
-This configuration of the global circulation is unstable
-Eartyhs rotation means the Coriolis force must be included

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96
Q

Describe the three-cell model:

A

-The coriolis force deflects flows to the right in the Northern hemisphere (and to the left in the SH)
-Hadley cell in the tropics and polar cells at high lattitudes have the same sense of circulation as single cell model
-The ferrel cell in mid-lattitudes in opposite sense
-Westerly (flow from W to E) jet streams ( at ~10km altitude) between cells
-Easterly surface winds in the tropics
-This configuration is more stable, but not completely and produces weather variability

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97
Q

Whhat is the Chaos theory and the Lorenz attractor?

A

-A set of physical equations that describe the weather
-These are non-linear and have sensitive dependence on the initial conditions
-They behave chaotically
-This is a physical explanaition for the variability of the weather (it is random but constrained within limits)

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98
Q

What is climate?

A

The long-term temperature mean

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99
Q

What is used in the Probablility density function?

A

Mean and SD

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99
Q

How else can you express the probablity distrubution of temperature?

A

the Return period

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100
Q

What do climate extremes generate?

A

Hazards- even for an unchanging climate

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101
Q

When does climate NOT change?

A

Under ‘Normal’ conditions

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102
Q

What is the effect of the (fast) changing climate?

A

-Changing PDFs and hence hazard frequencies/magnitudes
-This is fundamentally different to seismic and volcanic hazards
-Exposure is also increasing as global population rises

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103
Q

Whst is a heatwave?

A

Prolonged period of excessive heat

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104
Q

What does prolonged mean?

A

Typically at least 3 consecutive days in duration

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105
Q

What are the two types of excessive heat?

A

-Above a specific temperature threshold (e.g. 30C)
OR
-Above a percentile based on climatology for that location and time of year

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106
Q

Why is the met office no longer using the older climatology to establish thresholds?

A

-As heatwaves would occur more frequently
-We are adapting to cope with higher temperatures
-Hence dont need a temperature warning so often

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107
Q

Where do heatwaves tend to occur?

A

In mid-lattitudes (30-60 degrees N/S)

108
Q

What type of pressure is usually associated with heatwaves?

A

High surface pressure (Anticyclones)

109
Q

What type of weather is often brought by anticyclones?

A

Sunny and settled weather

110
Q

What is atmospheric pressure due to?

A

The weight of the overlying air

111
Q

What is the typical surface pressure?

A

100000Pa

112
Q

Why does the mass of a column of atmsophere vary from play to place?

A

Due to variations in air density, due to:
-The air being warmer/colder
-How much moisture it contains (moist air is less dnese than dry air)
-Cold/dry column ->High surface pressure
-Hot/wet column -> Low surfce pressure

113
Q

What creates winds?

A

Horizontal pressure gradients

114
Q

What do closer isobars mean?

A

-Stronger pressure gradient
-Stronger wind required for Coriolis force to balance pressure gradient

115
Q

What happens to wind when there is a balnce between pressure gradient, Coriolis and frictional forces?

A

-Wind is reduced and flows across the isobars towards low pressure
-so aire tends to spiral away from areas of H pressure to areas of L pressure

116
Q

How does low pressure affect vertical air motions?

A

Leads to convergence of air and hence ascent

117
Q

How does high pressure affect vertical air motions?

A

Leads to divergence of air and hence descent

118
Q

Compare vertical and horizontal velocities:

A

Vertical velocities (~cm/s) generally low compared with horizontal wind speeds (~m/s)

119
Q

How does temperature change with air height?

A

-Tempareture decreases with height
-As air cools as it rises

119
Q

How are anticyclones associated with heatwaves?

A

-An AC has air spiralling away from it at the surface and this creates decent
-Descending air gets warmer
-Assuming total water content is conserved, this means the air gets less saturated, so any clouds (liquid H2O) will evaporate (to water vapour)
-So anticyclones tend to be cloud-free and sunny
-In the summer they generate hot and sunny weather
-AC are quite stable and slow-moving, so they can persist for several days and lead to heatwaves
-weel spaced isobars-low winds-can accumulate air pollution

120
Q

Describe the affect of air temperature on saturation vapour pressure:

A

-Warmer air can accomodate more water vapour molecules than colder air
-So when air rises and cool it cant hold as much water as vapour so it condenses and forms clouds and rain

121
Q

What are the several measures of heatwaves?

A

Frequency,duration and Intensity

122
Q

Where are the steepest temperature gradients?

A

-Mid-lattitudes
-This is equivalent to a weather ‘front’ ; a boundary between warm and cold air
-Small disturbances (‘waves’) alog this front grow into storms

123
Q

Where does air pick its characteristics from?

A

The surface that it flows over

124
Q

What air is met at mid-latitudes?

A

Cold air from the poles meets warm,moist air from the tropics

125
Q

What are weather fronts?

A

Boundaries between air masses

126
Q

What can develop into warm sector depressions?

A

Waves on the polar front

127
Q

What are the stages of a life cycle depression (in the Northern hemisphere) ,using the Norweign model?

A

-Small low P develops-anticlockwise circulation
-Cold front is moving faster than the warm front
-Cloud/rain associated with frontal ascent
-Peak winds and tight isobars
-Low fills and storm dissipates
-Typical development and decay over a timescale of a few days

128
Q

What is needed for a cyclone to develop?

A

Divergence of air above is needed for surface low pressure to deepen

129
Q

What occurs when there is a divergence of air above?

A

When the jet stream bends

130
Q

What is needed for storm development?

A

-Divergence downwind of an upper level trough
-So there is an alignment of surface and upper level pressure patterns
-Optimal conditions can lead to very rapid storm development

131
Q

How do meteorologist try to forecast storm development?

A

Tracking the jet stream (upper level winds)

132
Q

What do slower-moving satorm mean for duration?

A

Higher accumulated precipitation which can last for up to several days

133
Q

How is Climate change affecting storm precipitation totals?

A

CC means that the atmosphere contains more water vapour, so higher rsinfall potential

134
Q

What are the storm characteristics which have evidence of being changed by climate change?

A

-Intensity
-Size
-Speed of passage

135
Q

Why do tropical storms not from from the Equator to +/_ N/S?

A

Lack of Coriolis force

136
Q

At what temperature do TS form?

A

> 27C

137
Q

Where do TS not form?

A

SE Pacific and S Atlantic as it is too cold

138
Q

Where do most TS form?

A

W pacific as it is a warm pool

139
Q

What makes an extra-tropical cyclone?

A

Wheb tropical cyclones travel into mid-lattitudes

140
Q

What classes as a cat. 1 storm on the Saffir-Simpson scale?

A

P>980hPa
64-82 knotts

141
Q

What classes as a cat.5 storm on the Saffir-Simpson scale?

A

P<920hPa
>135 knots

142
Q

Describe the formation of a tropical storm:

A

-Ocean evaporation
-Air spirals inwards and convects upwards
-Water condenses to form clouds
-Latent heat is released
-Results in warming the core of the TS
-Lowers pressure
-Pulls more surface inwards (positive feedback loop)

143
Q

Can a TS be self-sustaining?

A

Yes, it can be a self-sustaing heat engine as long as environmental conditions are favourable

144
Q

What happens in the centre of a Tropical storm?

A

-Descent at centre tends to dissipate clouds (eye)
-Surface winds spiralling inwards angular momentum
-So highest winds NEAR the centre of the storm
-High pressure in the eye

145
Q

What are scattomeres used for?

A

-Infer wind speed and direction from looking at sea roughness (from satellite data)
-They transmit a pulse of EM radiation and measure the returned backscatter, which varies with sea state.

146
Q

What type of wind shear do Tropical storms need to from?

A

Low wind shear

147
Q

At what side storm surges worse in the Northern hemisphere?

A

Right hand side

148
Q

How does El Nino affect Hurricanes?

A

-Fewer Atlantica hurricanes
-More Pacific hurricanes

149
Q

How does La Niña affect Hurricanes?

A

-More Atlantic hurricanes
-Less Pacific hurricanes

150
Q

How does Saturation vapour pressure chaneg with temperature?

A

Saturation vapour temperature increases with temperature

151
Q

How does climate change affect water content in the atmosphere?

A

Incraeses water in the atmosphere leading to more precipitation

152
Q

What do the IPCC predict will increase with climate change regarding tropical cyclones?

A

-Increase in average peak TC wind speeds
-Proportion of cat.4-5 TCs will increase in limited region over the Western-North Pacific
-Average TC rain rates will increase
-The global frequency of TCs over all categories will decrease or remain unchanged

153
Q

Can high winds mix Ocean?

A

Yes, high winds vertically mix ocean - and can leave a ‘cool trail’

154
Q

When does runoff peak?

A

Some time after peak rainfall

155
Q

What is lag-time determined by?

A

Intervening catchment hydrology:
-Forested hills (G)
-Poorly drained peatlands (G)
-Bare rock with thin soils (B)
-Urban areas (B)

156
Q

What are sustainable urban drainage systems?

A

Aim to increase retention of water in ponds to increase transit time

157
Q

What factors can be used in aiding flood prediction?

A

-Precipiation distribution and magnitude in time and space
-Transit time from where precipitation falls to the receptor location

158
Q

What models are used to ensemble weather forecasts?

A

Coupling rainfall and hydrology models

159
Q

Define drought:

A

-A prolonged absence oe marked deficiency of precipitation that results in water shortage
OR
-A period of abnormally dry weather sufficiently prolonged for the lack of precipitation to cause a serious hydrologicla imbalance

160
Q

How is drought severity assessed?

A

-Standardised Precipitation Index (SPI) measures how proabable the observed level of precipitation is compared to long-term data (i.e ver low prob. -> rare precipitation deficit)
-The Palmer Drought Severity Index (PDSI) measures the soil moisture content
-Planners may consult one or more indices before making desicisions

161
Q

Give an overview of the SPI:

A

-Based on the likelihood of precipitation (ONLY) for any time scale
-Used by many drought planners
-Can be computed for different time scales
-Can provide early warning of drought
-Assess drought severity
-Less complex than the PDSI

162
Q

Give an overview of the PDSI:

A

-A soil moisture index that differs with region
-Based on the concept if water balance: water supply precipition), demand (eavpotransipiration) and loss (runoff)
-It is used by many U.S government agencies and states rely on the PDSI to trigger drought relief programs
-Pros: The fist comprehensive drought index developed in the U.S
-Cons: Palmer values may lag emerging droughts (meteorological) by several months; complex

163
Q

What are droughts, heatwaves and high windspeed all relted to?

A

Wildfires

164
Q

How can large fires generate their own storms?

A

-Air is sucked in
-Smoke plume rises and cools
-Water vapour condenses froming a cloud
-Can cause downburst of rain and lightning
-And can add smoke to the stratosphere (15+ Km altitude)

165
Q

What is easily ignited by wildfires?

A

Dry vegetation

166
Q

What is short-term waether prediction?

A

A forcasting problem

167
Q

Describe wreather forecasting:

A

-The evoloution of weather is a chaotic system, so has sensetive dependence on initial conditions
-Some situations are more predictabel than others

168
Q

What is ensemble forecatsing used for?

A

-Used to quantify forecast probabilities
-Probabilities guide forecasts of hazard warning

169
Q

What does it mean if all the members look similar in ensemble forecasting?

A

The forecast is more predictable and hence more reliable

170
Q

With global warming, what warms faster, the Polar regios or the tropics?

A

The polar regions warm faster than the tropics

171
Q

What are the impacxts of global warming on global circulation?

A

-Not yet fully understood
-Predicted that the Tropics (Hadely cells) will widen
-Energy drirving the mid-lattutude cyclones will reduces, making weather systems move more slowly
-Small shifts in the global circulation could have major impacts e.e on monsoon rain systems

172
Q

What is sound?

A

-A wave (transport of energy)
-Simple pressure waves made from vibations

173
Q

What do vibrations cause air to do?

A

Cause air to expand and compress, creating series of high pressure -low pressure areas

174
Q

How do you find the source of sound?

A

-Measure time
-Know velocity
-Caulcaluate distance using:
Distance= velocity x time

175
Q

How many types of seismic waves are there?

A

4 types of seismic waves (one is also a pressure waves)

176
Q

How and where do Seismic waves travel?

A

-Travels mainly in solids (rocks)
-More complicated propagation

177
Q

Describe Body waves (1 type of seismic waves):

A

-Can travel through Earth’s interior
-P and S waves
-Arrives first

178
Q

Describe Surface waves ( 1 type of seismic waves):

A

-Only propagate at the interface between two different media (e.g Earth’s surface)
-Rayleigh and Love waves
-Arrive after Body waves
-Cause most destruction

179
Q

How are seismic waves recorded?

A

3-Component seismometer; one vertical component and two hprizontal components

180
Q

What is the arrival order of seismic waves, shown on a seismogram?

A

-P waves
-S waves
-Love waves
-Rayleigh waves

180
Q

What is a seismogram a representation of?

A

Ground motion:
-Z (Vertical)
-North-South
-East-West

181
Q

What do seismic waves from an EQ look like on a seismogram?

A

-P waves are the strongest on the veryical component
-S waves are strongest on the horizontal comment, often stronger on one than the other
-The faster the Love waves vibrate on the horizontal components only
-Rayleigh waves on both the vertical and horizontal components

182
Q

What are the propoerties of waves?

A

-Amplitude
-Wavelength
-Frequency
-Velocity

182
Q
A
183
Q

What is amplitude?

A

Height of crest or trough, measure of the energy of the wave

184
Q

What is wavelength?

A

-Distance between peaks or troughs (metres)

185
Q

What is frequency?

A

The number of waves passing per second (1/sec = Hz)

186
Q

What is wave velocity?

A

Frequency x Wavelength (m/s)

187
Q

What alters seismic wave velocity?

A

The ealstic properties of the medium

188
Q

Do P waves or S waves have a higher velocity?

A

P waves

189
Q

What is seismic wave attenuation?

A

Attenuation is the decay of amplitude with distance travelled

190
Q

What are the two types of sesimc wave attenuation?

A

1.Geometric spreading
2.Scattering

191
Q

What is geometric spreading?

A

-A decay in amplitude ,A, with distance ,d
-A~1/d for bosy waves, which spread out on a spherical wave front
-A~1/root d for surface waves, which decay more slowly (they don’t propagate vertically)

192
Q

What is scattering?

A

-Amplitude is rduce by ultiple reflections, refractions and mode conversions through 3D heterogeneities
-Results in a chatoic ‘coda’ to the seismogram, as well as making the S-wave arrival sometimes hard to pick

193
Q

Explain surfacw wave dispersion:

A

-Longer wavelengths (lower frequenices) penetrate deeper and arrive first
-This lead to different frequencies travelling at different speeds in a layered Earth. This ‘stretches out’ the waves packet, a process known as dispersion

194
Q

How can you calculate Epicentral distance?

A

Travel time:
S travel time - P travel time

195
Q

What is the general rule of thimb for erpicentral distance?

A

D~ (tS - tP) x 9

196
Q

Does an EQ fault slip all at once?

A

NO

197
Q

What shows EQ magnitude?

A

The area that moved (and the amount that it moved) is the size, magnitude, of the EQ

198
Q

Describe the nature of EQ rupture along a plane?

A

Although EQs are rupture of an area of a fault plane, they are often approximated (and plotted) as a point

199
Q

What is the hypocentre?

A

The origin point where the rupture started

200
Q

What is the epicentre?

A

The point on the surface above the hypocentre

201
Q

What is the centroid?

A

The centre of energy release, usually near the centre of the rupture area

202
Q

What does EQ magnitude measure?

A

The amount of energy released

203
Q

On which type of scale is EQ magnitude measured on?

A

-Logarithmic
-Increase in magnitudfe of 1, is 10 times increase in ground shaking (seismic amplitude)

204
Q

What is the relationship between magnitude and number of EQs?

A

Logarithmic

205
Q

What was the first EQ magnitude scale?

A

-Richter scale, but not in use today
-Only applicabble for Southern California only

206
Q

What are the principles behind all seismic magnitude calculations?

A

-Convert seismic amplitude to EQ magnitude
-Correct for distance
-Scale is logarithmic

207
Q

What are some problems that the richter scale has?

A

-Only valid for one type of seismometer
-Dependent on local geological conditions
-Only valid for local EQs (called a local magnitude scale)

208
Q

What are the disadvantages of modified scales?

A

-It depends on having a seismometer
-Strong saturation effect becasue large EQs release low-frequencies that are not measured notably

209
Q

What is the universal magnitude scale?

A

Moment magnitude scale

210
Q

What is a moment?

A

A physical quantity proportional to the slip on the fault multiplied by the area of the fault surface that slips

211
Q

How can moments be estimated?

A

The moment can be estimated from seismograms (and also gfrom geodetic measurements)

212
Q

How to measure moment magnitude?

A

M0= rigidity of rock x rupture area x displacement

213
Q

Describe the dirtrubution of frequency and intensity of EQs over time?

A

There are small- and moderate-sized EQs that occure frequently around the world that release far less energy than a single great EQ

213
Q

What is the largest theoretical EQ magnitude?

A

If all subduction zones and other structures in the world ruptured at the same time, it would be an EQ of ~Magnitude (Mw) 10.5

214
Q

Why is Mw 10.5 EQ deemed impossible?

A

EQ rupture areas are thought to be limited by barriers, such as:
-Changes in the geometry of a fault
-Changes in rock composition along a fault
-Changes in temperature

215
Q
A
216
Q

What is the Guternberg-Rihter relationship?

A

Log 10 (N) =a - bM
-N is the no. of EQs of Mw > M
-a is a measure of th total number of EQs (activity level) in the region
-b decribes the relative proportions of large and small EQs and is close to 1.
-b depends on regional stress state in the crust

217
Q

What does a low b value in a Gutenberg-Richter relationship mean?

A

-Low b value -> more large EQs relative to small EQs -> Possibly higher crustal stress

218
Q

What is the completeness magnitude?

A

The magnitude above which all EQs occuring in a region are recorded

219
Q

What do a and b provide information on?

A

They provide crucial infromation on the seismicity rate of a region (how many EQs if a certain Mw happen over a specific period of time) and are an important part of seismic hazard analysis

220
Q

Describe Earthquake recurrence:

A

-The rate of EQs on faults is governed by the size of the fault and the rate that one slide moves relative to the other
-Larger faults can have larger EQs
-Faults with higher slip rate have more frequent EQs

221
Q

What are ‘characteristic’ EQs using the idealised ‘Characteristic’ EQ model?

A

Large EQs on a fault are always the same magnitude and occur at a constant recurrence interval

222
Q

What can be EQ recurrence be estimated from?

A

-Historical data
-Paleosismic data (geomorphology, geology)

223
Q

Why does the idealised ‘charactertistic’ EQ model not work?

A

-Stress loasing rate varies over time
-Fault strength (failure stress) changes over time
-Stress drop in each EQ is different
-Faults influence each other
-Small EQs can release stress during interseismic cycle

223
Q

What are seismic hazards measured in terms of?

A

Ground motion probabilities

224
Q

What influences seismic hazards?

A

-Distance from seismic sources
-Magnitude of potential EQs
-Frequency of occurence of EQs (as a function of size)
-Attenuation of ground shaking (with distance from source)
-Frequency content of ground shaking
-Duration of round shaking
-Local side effects

225
Q

What is a time-independent seismic hazards assessment?

A

-There is no memory of past events: EQs can happen at any time at a constant rate of probability
-Based on long term-averages of EQ sources
-Has 4 main components; sources, recurrence, ground motion, probability of exceedance

226
Q

Describe the positives of using Seismic sources?

A

-Identifictaion of sources locations EQs, active faults, areas of strain accumulation
-Group areas into zone (can be subjective)

227
Q

Describe the negatives of using Seismic sources:

A

-Not all events may be recorded
-Not all faults produce large EQs (creeps)
-Not all faults are known

228
Q

Describe the positives of using Recurrence:

A

-Known as the Gutenberg-Richter relation
-The maximum magnitude is estimated from the largest previous event or from fault length

229
Q

Describe the negatives of using Recurrence:

A

The largest events often dominate the hazard rate, but they are so rare, so their recurrence frequencies are very uncertain

230
Q

What are ground motion curves?

A

-Plot ground motion as a dunction of distance for different magnitudes
-The largest events have highest ground motion and propagate to larger distances
-Larger scatter in the attenuation data
-Scatter is due to; geological inhomogeneities along the ray path (wave scattering), local site conditions

231
Q

What are the positives of using Ground motion prediction:

A

-Predict fround motion based on distance, magnitude and style of faulting
-Often measured in terms of acceleration or gravitational acceleration
-Immensely useful since simple to use

232
Q

What are the negatives of using Ground motion prediction:

A

-Limited to regions with sufficient data (EQs and seismic stations)
-Treats EQs as a point
-Doesn’t count for complex seismic wave propogation
-Don’t always account for local site effects

233
Q

What do ground motion using physics based simulations show?

A

Include site-specific geological structures (e.g. sedimentary basins) and source-specific parametres (e.g. slip distribution, rupture directivity, rupture velocity)

234
Q

What is probability of exceedance?

A

-Combines sources,recurrence and round motion as a composite plot of the probobility of a given site experiencing a given level of ground shaking
-Green lines show how cost-benefit analysis determines a probability (relative to ither risks) , which in turn determines an acceleration for design purposes

235
Q

What do seismic hazard maps show?

A

Produce probability of exceedance curves at every location in a region

236
Q

What are the uses of time-independent hazards?

A

-Town and country planning -> Land use
-Setting building design codes
-Eductaion
-Setting EQ insurance premiums -> spreading the risk

237
Q

What are time -dependant hazards?

A

-Hazards given by background rate multiplied by a conditional probability that depends on the size and time of previous events

238
Q

Why are time-depend predictictions more accurate than assumung time-independent hazards?

A

Where there has recently been a big EQ, seismic energy has now been dissipated and there should now be a long period before it builds up again

239
Q

What do strong contiguous clusters at a given time reveal?

A

Reveals the source rupture length from the early aftershocks

240
Q

Why can neighbouring fault segments be triggered at the same time?

A

Due to stress transfer

241
Q

What is a main shock?

A

Identified by its size, as the largest event in an EQ sequence

242
Q

What is a foreshock?

A

A smaller evnt that preceded the main shock. Not all mainshocks have foreshocks

243
Q

What are aftershocks?

A

-Events that come in the months, years or even decades following the mainshock.
-They occur with 1-2 fault lengths distance from the mainshock faults ans are smaller, often one Mw less

244
Q

What is stress transfer?

A

-EQs can increase/ decrease stress on neighbouring faults
-Aftershocks tend to occur in areas with a stress increase

245
Q
A
245
Q

Are EQs more disastrous now then they were in the past?

A

Yes, not becasue EQ frequency is increasing but due to increasing fatalities related to urbanisation

246
Q

What is increasing urbanistaion leading to?

A

Greater exposure and vulnerability

247
Q

What is strengthening of buildings?

A

Basic strengthening of buildings are required by law - and still experince violent shaking and some damage

248
Q

What is damping of buildings?

A

Dampers absorb energy - lead to reduced shaking

249
Q

What is isolation of buildings?

A

Most expensive option, building isolated from the ground -to result in ONLY a slow shaking

250
Q

Describe the realtionship between the frequency of buildings and the ground?

A

-Buildings have a natural resonance frequency: the frequency at which maximum amplitude occurs
-If the ground motion matches the natural resonance frequency of a building it will undergo large oscillations and suffer greatest damage
-Small buildings oscillate at higher frequencies than larger ones
-The ground also has a resonance frequency

251
Q

How can risk be calculated?

A

Risk = Hazard x Exposure x Vulnerability
-Combines hazard (ground motion probabilities) with exposed structures/facilities (e.g. buildings, bridges, electricall power switching stations) and their vulnerability (or fragility)
-Calculated in terms of probabilities for economic damage or casualties
-Acquiring and analysing the specific data for an individual building or facility

252
Q

What are the properties of exposure?

A

-Physical components are buildings and infrastructure
-Location
-Economic value
-Occupants
-Number of stories
-Use
-Construction type

253
Q

What can be done to mitigate and prepare?

A

-Better building codes, that are enforced
-Map seismic site conditions to prevent building in certain regions
-Education; EQ drills, museums, EQ ‘monuments’ , cultural legacy

254
Q

What are EQ early warnings?

A

-Quickly identify an EQ and issue and alert before widespread shaking is felt
-Relies on detecting fastest (and weakest) waves, P-waves, then computing an events location and magnitude
-Depending on distance, the alert may reach people before the more destructive S and Surface waves, giving people time to prepare (drop, cover, hold)

255
Q

How does MyShake operate?

A

Uses smartphones as EQ sensors, a lot of smartphones and a lot less expensive than a traditional seismic network- hence can be used anywhere in the world

256
Q

What are the problems of EQ early warning systems?

A

-Cannot tell magnitude very accuraetkey from the first few seconds of P waves
-Smart phones are concentrated i cities, but EQ often happen in remote areas, so still need conventional seismometers
-False alert reduces the confidnece of users
-Needsb to be implemented along with public eduction (no use warning people if they don’t do anything)

257
Q

What are cascading hazards?

A

-New, secondary hazards triggered by the primary hazard
-Secondary hazards may begin in small area but impact a wider region than the primary hazard

258
Q

What is liquefaction?

A

-The phenomena when solid soil behaves temporarily as a viscuos-liquid
-Occurs when loosely packed, water-logged sediments lose their strength in response to strong ground-shaking
-Soil loses ability to support foundations of buildings
-Most commoly obsered in low-lying areas near bodies of water

259
Q

How does agriculture affect susceptibility to liquefaction?

A

Agricultural (rice) irrigation elevated the water table, increase the liquefaction susceptibility. -Can cause landslides to occur on very shallow slopes that would otherwise be stable

260
Q

What are tsunamis caused by?

A

Caused by a sudden vertical discplacent of ocean water

261
Q

What are the principles of tsunamis?

A

-Tsunamis travel at a speed that is realted to water depth (D)
-Tsunami wave velocity = root (gD)
-Tsunamis slows as the water depth decreases
-The tsunamis energy flux, which is dependant on both its wave speed and wave height, remains nearly constant -> speed reduces and height grows in shallower waters

262
Q

What are meteotsunamis caused by?

A

Caused by fast-moving pressure waves in the atmosphere

263
Q

What are ways in which to achieve Tsunami risk reduction?

A

-Sea walls
-Awarness and education; if feel shaking and close to coastal area then get to high ground, clearly marked tsunami evaxuation routes, tsunami drills

264
Q

How can tsunamis be warned from EQs?

A

Government monitering agencies often issue tsunami warnings based on whether an EQ the has just been detectd is likely to cause a tsunami. Warnings are iften issued on public systems installed in coastal areas.This is based on rapidly finding out:
-Loction of the EQ (offshore)
-Depth of the EQ (shallow depth to move the seabed)
-Magnitude of the EQ
-The focal mechanism of the EQs (thrusts are most likely to cause EQs)

265
Q

What are Tsunami early warnings?

A

-Monitoring network that detects tsunami waves and can provide early warning
-DART (Deep-ocean Assessment and Reporting of Tsunamis) focused on the Pacific Ocean
-Signal sneer via satellite to the tsunami warning centre
-Only useful for places sufficiently far from the source fopr warning to be used

Y1,S1-Natural Hazards (2 decks)

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