natural hazards Flashcards
name the 4 -spheres on earth
atmosphere
biosphere
hydrosphere
geosphere
Tonga eruption
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
layers of the atmosphere
- troposphere (0-12km)
- stratosphere (12-50km)
- mesosphere (50-80km)
- thermosphere (80-700km)
- exosphere (>700km)
The 12 Smart 50g Mice Took 700 Extra cheese
why are there so many natural hazards on earth?
- 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
natural hazard
natural process that poses threat to human life or property
natural disaster
natural event that causes significant damage to life or property
catastrophe
atrial event that kills or injures large numbers of people or causes extensive property damage
why are there more deaths due to heat waves and floods compared to earthquakes?
dramatic hazards occur infrequently and in restricted areas
can also be predicted more accurately and there are more evacuation plans in response
hazard related death %
- heat and drought (27.8%)
- flood (16.3%)
- winter weather (14.9%)
- earthquake and tsunami (1.9%)
- volcano (0.2%)
why is there significant variation in fatalities from year to year?
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
difficulty in predicting catastrophes
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
recurrence interval
the past occurrence of random events
forecasting
the future likelihood of random events
magnitude and frequency relationship
magnitude is inversely proportional to frequency
relationship among earthquake events
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
positive feedback
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
negative feedback
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
mitigating hazards
these efforts prep for a disaster and reduce its damage
eg. engineering projects, government policies, public education
- land use planning
- insurance
role of government in mitigation efforts
research nature and behaviour of natural hazards
advocate for public education
what are the 4 earth layers
- crust (oceanic: <10km, continental: 70km)
- mantle (2900km, liquid)
- outer core (liquid)
- inner core (solid)
Alfred Wegener
Continental drift theory
who theorised about the continental drift
Alfred Wegener
continental drift
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
evidence to support the continental drift theory
fit of the continents
location of glaciations
fossil organisms
rick type and structural similarities
paleoclimates preserved in rocks
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
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
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.
does the magnetic field of the earth change its polarity through time?
yes, the polarity will flip every few million years
what material is the core made of?
iron and nickel
what are the 3 types of plate boundaries
- convergent
- divergent
- transform
oldest ocean floor is the _______________.
a. shallowest
b. deepest
b. deepest
reason: the older the rock, the cooler it is, becomes denser and sinks
oceanic crust is __________ than continental crust
a. denser
b. less dense
a. denser
convergent plate boundary examples
continental-continental convergence
Indian and Eurasian plate
forming Himalayas mountain range
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
convergent plate boundary examples
oceanic-oceanic convergence
Pacific and Mariana/Philippine plate
Mariana trench
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
transform plate boundary examples
(continental-continental) Pacific and N. American
San Andreas fault
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
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.
p-wave
move horizontally, side to side, particles move parallel in the direction of the wave
also known as a compression wave
p: push
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
what are body waves
p- and s-waves
waves in order of descending speeds
p > s > surface
p is fastest
surface is slowest
what are the 3 kinds of earthquake faults
- reverse/thrust fault
- strike-slip
- normal fault
eg of reverse fault
Taiwan, at convergent plate boundaries
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
eg of normal fault
Nevada, Greece (Taygetos mountains), divergent plate boundaries
M0 stands for
seismic moment
Mw stands for
moment magnitude
hypocenter
the point where an earthquake or an underground explosion originates
epicenter
the point on the Earth’s surface directly above the hypocenter/focus
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