natural hazards Flashcards
1
Q
name the 4 -spheres on earth
A
atmosphere
biosphere
hydrosphere
geosphere
2
Q
Tonga eruption
A
undersea volcano erupted, sending gas and ash > 50km into the atmosphere (into mesosphere)
explosion was around the size of Australia
the pressure waves triggered a tsunami
oceanic-oceanic plate
3
Q
layers of the atmosphere
A
- troposphere (0-12km)
- stratosphere (12-50km)
- mesosphere (50-80km)
- thermosphere (80-700km)
- exosphere (>700km)
The 12 Smart 50g Mice Took 700 Extra cheese
4
Q
why are there so many natural hazards on earth?
A
- dynamic earth with moving plate tectonics
- everyday, the plates move little by little but as the energy accumulates, one day there will be a sudden release of energy that causes a catastrophic event
5
Q
natural hazard
A
natural process that poses threat to human life or property
6
Q
natural disaster
A
natural event that causes significant damage to life or property
7
Q
catastrophe
A
atrial event that kills or injures large numbers of people or causes extensive property damage
8
Q
why are there more deaths due to heat waves and floods compared to earthquakes?
A
dramatic hazards occur infrequently and in restricted areas
can also be predicted more accurately and there are more evacuation plans in response
9
Q
hazard related death %
A
- heat and drought (27.8%)
- flood (16.3%)
- winter weather (14.9%)
- earthquake and tsunami (1.9%)
- volcano (0.2%)
10
Q
why is there significant variation in fatalities from year to year?
A
major events are rare and they contribute to the largest number of deaths
fatality in developing countries is much higher so it depends where the earthquake hits
11
Q
difficulty in predicting catastrophes
A
there are only v few well-documented instances of prediction
some natural events have predictable cycles but these often overlap with one another and cause complications in predictions
however, forecasting hazardous events are possible even in certain areas within a few decades
the past is the key to the future, we need to refine past records and estimate the recurrence interval
12
Q
recurrence interval
A
the past occurrence of random events
13
Q
forecasting
A
the future likelihood of random events
14
Q
magnitude and frequency relationship
A
magnitude is inversely proportional to frequency
15
Q
relationship among earthquake events
A
some events are directly related to others and may overlap to reinforce each other
past events influence future events
some processes result in (positive/negative) feedback effects
16
Q
positive feedback
A
a feedback loops which exacerbates the effects of a small disturbance
eg. global warming causes arctic ice to melt, darker oceans absorb more heat, less reflection, cause more ice to melt, temp increases further
17
Q
negative feedback
A
where the product of the reaction leads to a decrease in that reaction
eg. temp increase, more evaporation, more clouds, clouds act as a cover, evaporation slows, temp decreases
18
Q
mitigating hazards
A
these efforts prep for a disaster and reduce its damage
eg. engineering projects, government policies, public education
- land use planning
- insurance
19
Q
role of government in mitigation efforts
A
research nature and behaviour of natural hazards
advocate for public education
20
Q
what are the 4 earth layers
A
- crust (oceanic: <10km, continental: 70km)
- mantle (2900km, liquid)
- outer core (liquid)
- inner core (solid)
21
Q
Alfred Wegener
A
Continental drift theory
22
Q
who theorised about the continental drift
A
Alfred Wegener
23
Q
continental drift
A
the theory that once, all the continents were joined in a super continent (Pangaea)
over a vast period of time, the continents drifted apart to their current locations
24
Q
evidence to support the continental drift theory
A
fit of the continents
location of glaciations
fossil organisms
rick type and structural similarities
paleoclimates preserved in rocks
25
why was wegener’ s idea rejected?
the crust and mantle were thought to be solid thus could not move therefore it was stupid to think that the continents drifted apart from each other
26
evidence supporting plate tectonics theory
Henry Hess
mapped ocean floor bathymetry, revealed strange topography of ocean floor (there’s ridges, trenches, and valleys)
global seismicity shows the shape and outline of the plate boundaries
deeper seismicity indicate that the heavier plate has been subducted into the deeper part of the earth
magnetic anomaly supports sea floor spreading
mid-ocean ridge higher than nearby sea floor shows convergence
27
magnetisation patterns on sea floor
alternating +/- magnetic signature of ocean floor materials
through this, we can estimate the age of oceanic lithosphere bc plates move ~3cm per year
when lava gets erupted at the mid-oceanic ridge axis, it cools and turns into rock. as it cools, it becomes permanently magnetised in the direction of the earth’s magnetic field. the earth’s polarity flips every few million years and this can be recorded in the sea floor. at the mid-oceanic ridge spreading axis, these flips are recorded thus creates a symmetrical pattern of magnetic strips of opposite polarity on either side of the mid-oceanic ridge.
28
does the magnetic field of the earth change its polarity through time?
yes, the polarity will flip every few million years
29
what material is the core made of?
iron and nickel
30
what are the 3 types of plate boundaries
1. convergent
2. divergent
3. transform
31
oldest ocean floor is the _______________.
a. shallowest
b. deepest
b. deepest
reason: the older the rock, the cooler it is, becomes denser and sinks
32
oceanic crust is __________ than continental crust
a. denser
b. less dense
a. denser
33
convergent plate boundary examples
continental-continental convergence
Indian and Eurasian plate
forming Himalayas mountain range
34
convergent plate boundary examples
oceanic-continental convergence
Nazca (oceanic) and South America (continental) Plate
Peru trench and Andes mountain on the S. America plate
can also form volcanoes
35
convergent plate boundary examples
oceanic-oceanic convergence
Pacific and Mariana/Philippine plate
Mariana trench
36
divergent plate boundary examples
Eurasian and North American plate
(oceanic-oceanic) mid-atlantic ridge > in the water
African and Arabian plate
(continental-continental) East African rift valley > on land
37
transform plate boundary examples
(continental-continental) Pacific and N. American
San Andreas fault
38
what causes an earthquake?
stress and strain
graph:
y-axis: stress
x-axis: strain
1. elastic deformation is reversible, can return to its original shape, rocks keep stretching until it reaches
2. plastic deformation which is not reversible, cannot return to its original shape, when it reaches the elastic limit, it can’t stretch and relax anymore which leads to
3. brittle failure where the fault slips, causing an earthquake due to the sudden dislocation
39
explain the elastic rebound theory
As the Earth’s crust deforms, the rocks on opposing sides of a fault are subjected to shear stress. Slowly they deform, until the rock strength is exceeded. Then they separate with a rupture along the fault. The sudden movement releases accumulated energy, and the rocks snap back almost to their original shape. The previously solid mass is divided between the two slowly moving plates, the energy is released through the surroundings in a seismic wave.
40
p-wave
move horizontally, side to side, particles move parallel in the direction of the wave
also known as a compression wave
p: push
41
s-wave
look like a sine curve
particles move perpendicular to the direction of the wave
slower than p-wave but has a bigger amplitude
s: shape of the wave
42
what are body waves
p- and s-waves
43
waves in order of descending speeds
p > s > surface
p is fastest
surface is slowest
44
what are the 3 kinds of earthquake faults
1. reverse/thrust fault
2. strike-slip
3. normal fault
45
eg of reverse fault
Taiwan, at convergent plate boundaries
46
eg of strike slip fault
San Andrea’s, Mekong river, if the opposite side move to the left, it is a left lateral strike slip and vice versa
47
eg of normal fault
Nevada, Greece (Taygetos mountains), divergent plate boundaries
48
M0 stands for
seismic moment
49
Mw stands for
moment magnitude
50
hypocenter
the point where an earthquake or an underground explosion originates
51
epicenter
the point on the Earth’s surface directly above the hypocenter/focus
52
fault scarp
a planar geomorphic feature formed by the offset of Earth’s surface by one or more earthquakes
—> the exposed part of the fault line
53
wavefront
a surface over which time of the wave have been propagated away from the hypocenter is the same
—> something like wavelength (the distance between 2 peaks)
54
the larger the fault area, the ,anger the earthquake
a. true
b. false
a. true
55
different types of earthquake hazards
ground shaking
surface faulting
landslides
flooding
liquefaction
changes in land level
tsunami
56
ground shaking
shaking is greatest near the earthquake source
1m/s
lasts a few seconds to several minutes
57
frequency
the number of waves that pass through a point in one second
58
period
amount of time it takes one wave cycle to pass through a given point
59
resonance
tendency of a system to oscillate with greater amplitude at some frequencies than at others
60
resonant frequency
the frequency at which the maximum amplitude oscillation occurs
61
to minimise shaking, short buildings should be on ________ bedrock while tall buildings should be on _________ bedrock.
soft, hard
62
when the amplitude is _______, the taller building will shake more violently and vice versa.
small
63
explain the meaning of tsunami
it is japanese for
tsu: harbour
nami: wave
bc it occurs in the harbours
64
wave vs tsunami
wavelength of a normal wave < tsunami
65
(tsunami) undersea rupture of normal/thrust/mega thrust faults
1933 Sanriku
2004 Indian Ocean
2011 Tohoku
66
(tsunami) undersea landslide
1958 Lithuanian Bay
Hawaiian islands
67
(tsunami) undersea volcanic eruptions
1883 Krakatau
1628BC Santorini
2022 Tonga eruption
68
(tsunami) asteroids
65 million years ago K-T extinction
Eltanin impact
69
velocity of a tsunami related to the depth of the sea
a. true
b. false
a. true
70
factors affecting height of a tsunami wave
- earthquake magnitude
- area of rupture zone
- rate and volume of water displaced
- sense of ocean floor motion
- depth of water above rupture
71
3 ways undersea volcano cause a tsunami
1. an enormous explosion displaces large quantities of sea water
2. the underwater portions of the volcano subside quickly during the eruption, gently disturbing the seafloor
3. large volumes of volcanic material enter the sea and displace sea water
72
tsunami from meteorite factors
can displace large amounts of water and generate tsunami
HEIGHT of fall has more effect than volume of mass (of the meteorite) that displaces the water
SPEED of the meteorite plays the most important role
73
shield volcanoes
more flat and wide, huge
because the lava is more fluid and less viscous
less explosive eruptions
eg. hawaiian islands: mauna kea, mauna loa, kohala, hualalai
74
stratovolcanoes
taller than shield volcanoes
lava has high viscosity
more explosive eruptions
eg. mt. vesuvius
75
caldera
looks like a hole in the ground
formed as a result of an ultra-plinian eruption, the most explosive
76
explosiveness of volcanoes
dependent on the viscosity of the lava, more fluid, less viscous, less gas trapped —>less explosive
from least to most explosive
shield volcano > stratovolacno > ultra plinian
77
igneous rocks
formed form crystallisation of magma during explosive eruption process
magma floats to the surface of the earth due to its buoyancy
due to density difference, magma can flow either vertically upwards or horizontally
magma more dense than the surrounding rock —> horizontal
magma less dense (can float) than the surrounding rock —> vertical, become intrusive rocks
78
extrusive rocks
igneous rocks
fine-grained and quickly cooled
lighter coloured rocks have higher % silica compared to darker rocks
79
intrusive rocks
igneous rocks
course-grained and slowly cooled (underground)
magma slowly rises from underground then flows outward rather than upward, hence not very explosive
heavier in comparison to extrusive rocks
80
classification of igneous rocks are by
-mineral composition
- grain size
- texture
81
metamorphic rocks
characterised by curved lines through the rock —> shows that there is some form of deformation (caused by pressure)
formed from other rocks (igneous and sedimentary) through heat and pressure underground
82
sedimentary rocks
characterised by layers in the rock
formed from layers of sand, silt, dead plants, and animal skeletons
83
silica and it’s effects on rock types
magmas range from about 50-70% silica
more silica in the rock —> lighter colour
more silica —> rock stiffer, more sticky, more difficult to move freely
basalt: 50% silica, erupt at higher temp, 1200 degrees
rhyolite: 75% silica, erupt at lower temp, 900 degrees
84
factors for explosive eruption
high temp
more fluid
less silica
more water
85
water and its effects on eruptions
the more water, the more explosive
more water, lower viscosity, more fluid, less stiff
water can evaporate to become gas bubbles, increase trapped gas = more explosive
86
describe a plinian eruption column
lava is sticky
cooler, lower temp
bubbles can’t expand or escape easily —> stay underground longer, higher pressure, causing a huge thrust of air and gas, leading to a bigger eruption
87
characteristics of a plinian eruption
ash and smoke column that can extend to the stratosphere
large amounts of pumice (extrusive igneous rock)
powerful gas blasts
large amounts of magma erupted
caldera formation
starts with glowing pyroclastic flows
forms lava domes with steep sides
most explosive
88
3 types of magma
1. basaltic
2. andesite
3. dacite
4. rhyolite
in order of increasing silica content, decreasing eruption temp and decreasing mobility of lava
89
3 parts of a plinian column
gas thrust
convection region
umbrella region (affected by wind direction)
90
3 types of volcano deposits
1. fall: blanket the ground with a nearly uniform mantle of fine particles (pyroclastic fall/air fall)
2. flow: dense slurries of debris racing down the slopes of the volcano, thicker and larger materials that will accumulate in the valleys, fill in the gaps
3. surge: clouds of debris-laden gas jetting out of the volcano and facing over the countryside forms layers of irregularly bedded ash and blocks, combination of fall and flow
91
volcanic hazards without eruption
ground shaking
fractures and fissures
outgassing
acid lakes
lahars and landslides
92
ground shaking (volcano hazard)
volcano related earthquakes are different from tectonic ones but the effects are similar
most earthquakes that result from volcanic eruptions are a magnitude 3
93
fractures and fissures (volcano hazard)
fracture in the ground occurs when there is magma opening in the ground
happens over time, opens gradually
94
outgassing (volcano hazard)
volcanoes leak gas (even dormant ones leak)
high pressure underground causes magma to vapourise
gas consists of: CO2, sulphuric dioxide (a smelly gas), a person can suffocate due to the concentrations of this odourless gas
eg. mammoth mountain is considered active due to outgassing but it does not erupt, plants around there die bc there’s too much CO2 in the soil
95
acid lakes (volcano hazard)
calderas collect water inside it and this water
when mixed with all those gases (CO2, SO2, HS, HCl, HF) become very acidic
can have a pH of 0.1
eg. Ijen crater lake in East Java and Toba
96
lahars and landslides (volcano hazard)
lahar is a volcanic mudslide
mixture of water, rock fragments, and soil
lahar flows: mud-like consistency that is filled with chunks of rocks and soil
lahars can be triggered by an eruption or heavy rain
move at 10+m/s
97
direct hazards of volcanic eruptions
- ground shaking
- fissures
- outgassing
- pyroclastic falls
- pyroclastic flows
- lava flows
- landslides and tsunamis
98
pyroclastic falls
volcanic ash is composed of small fragments of rock (micrometers)
it can
- reduce visibility (block sunlight) —> affects plants and animals
- damage engines of planes
- dense ones can collect and collapse roofs
- disrupt power generation, transmission, and distribution
- clog water supply
- cause breathing difficulty
- damage crops
99
pyroclastic flows
fast moving rocks and gas
high density mixtures of hot and dry rock fragments and hot gasses
you can escape if you have lead time
pyro: fire
clastic: broken
speed: faster than 80km/h
temp: 200-700 degrees celcius
can cause chokes in rivers or dams that result in floods
100
lava flows
slow moving
high temperature
will destroy anything in its path
least hazardous of all but it’s biggest hazard is to property
101
factors affecting rate and distance of lava flow
temperature: high
silica content: low
extrusion rate: high
slope of land: steep
lava will travel further and faster
102
landslides and tsunami (volcano hazard)
landslides are large chunks of mountain flowing away
these chunks fall into the water body and cause tsunami
eg hawaiian islands
103
indirect hazards with volcanic eruption
- air travel effects
- climate change
104
examples of air travel effects due to volcanic eruption
KLM flight 867 (1989)
- flight flew through a thick cloud of volcanic ash from mt redoubt
- all 4 engines failed, captain used backup power to try and restart the engines
- eventually succeeded after descending 4300m
- aircraft is still in service (after USD$80 million in repairs)
- rocks and debris from the volcano get stuck in the engines and cause abrasions, contaminated the electrical, hydraulic and fuel systems
Eyjafjallajokull eruption case
- largest breakdown of european airspace
- economic loss of USD$4.7 billion in 1 week
- business and leisure delayed or cancelled, perishable goods industrial plants suspended production
Kelut (2004)
- recent eruption shut down the airport in SEA including SG
105
how can volcanic eruption cause climate change?
temperature drop
- volcanic ash physically block sunlight causing global temps to drop
- eg. pinatubo (1991): temp drop by ~0.5C
mt. tabora (1815): temp drop by ~0.4-0.7C, year without summer, crops don’t grow, famines, epidemics occurred
toba: ash widespread, 15cm thick over the indian subcontinent, 6cm thick in central india
temperature rise
- can trap ghg under the layer of volcanic ash cloud
106
what is a super volcano and cite examples
any volcano capable of producing a volcanic eruption with an ejecta volume greater than 1000km3
- Taupa (NZ)
- Yellowstone
- Cerro Galan, Argentina
- Pancana, Chile
- Toba, Sumatra: estimated 2800km3 of material, pyroclastic flows over 20, 000km2, ash deposits up to 600m thick,caused volcanic winter, more than 95% of animals and plants in SEA died
107
explain what is volcano monitoring and list examples
study historical events to know what to plan for
- volcanic tremor (using seismic signals indicating magma movement)
- ground deformation (GPS, InSAR, Tiltmeter)
- gas monitoring: collect gas samples to tell us about the chemical processes within the volcano
108
how does a tiltmeter work
measure tilt of the ground
as magma wants to come up from underground, it pushes against the ground, slowly there is a tilt to the ground
109
how does seismic tomography work
similar to MRI or X-ray but for the ground
can map the magma chambers underground
110
how to use infrared for volcano monitoring
view the presence of magma beneath the surface
111
how does InSAR work
map surface displacement (how the ground changes or moves over a period of time), as gas accumulates under the surface, the topography will change and become “taller”
112
how to use infrasound to do volcano monitoring
monitor underground pressure, when too much pressure, it will likely erupt
113
what is a landslide
movement of a mass dock, debris, or earth and/or mud down a slope
gravity plays a part bc the things move downward
rotational or translational
114
rotational landslide
moves downward and upward about curved slip surface
relatively deep
mone short distance
head (top) moves downward and rotates backward
toe (bottom) moves upward on top of landscape
115
translational landslide
move on a planar slip surface such as a fault, joint, clay-rich layer
move as long as on a downward-incline when there is a driving mass
underlying material falls so overlying material slides
remain coherent as a block
deform and disintegrate to form debris slide
116
debris flow
may be wet
117
creep
occur gradually
118
rockfall
rocks that slide or roll downhill
eg. Badouzi Taiwan 2013 due to rainfall
My Kinabalu 2015 due to earthquake
119
driving force
gravity pulls down material, external forces contribute (earthquake and eruptions)
120
resisting force
holds material in place, strength of material and amount of friction plays a part
121
factors contributing to slope failure
slope steepness
material weight
moisture content
122
angle of repose
steepest angle at which any loose material is stable
depends on angularity and size of grains and moisture content
123
sources of weakness for planar internal surfaces
layers in sedimentary rock
fractures in any kind of rock
contacts between rocks of different strength
faults or slip surfaces of old landslides
124
deltas
low lying landform created by deposition of sediment that is carried by a river as it enters slower-moving or stagnant water
Usually where a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment
125
age of big deltas
7000 yrs
126
important deltas in SEA
ganges-brahmaputra
- a v wide delta
- numerous distributors rivers
127
what drives sea level change
- global process (warming or cooling)
- land changes
- hydrological cycle
- atmosphere-ocean interaction
128
storm surge
A storm surge, storm flood, tidal surge or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems.
These include tropical and extra-tropical cyclones.
It is measured as the rise in water level above the normal tidal level, and does not include waves
129
compound flooding
compound = multiple happen together
definition by IPCC
(1) two or more extreme events occurring simultaneously or successively;
(2) combinations of extreme events with underlying conditions that amplify the impact of the events; or
(3) combinations of events that are not themselves extremes but lead to an extreme event or impact when combined. The contributing events can be of similar (clustered multiple events) or different type(s)
130
w response strategies to sea level rise
RETREAT - move, plan where you wan live
ADAPT - let natural system effects occur then u accommodate to the rises and minimise human impact
DEFEND - soft or hard engineering by building levees
