Paper 1: Section A: The challenge of Natural Hazards
Natural Hazards: A non-man-made / natural event (earthquake, volcanic eruption, tropical storm, flood) that
threatens people and property / has the potential to cause damage, destruction, and death. A natural event becomes
classified as a natural hazard when there is a threat to human life, activities, or property. A natural hazard becomes
classified as a natural disaster when it affects a population on a large, disastrous scale.
Geological hazards Hazards caused by processes on the land. Volcanos, Earthquakes, Landslides, Mudflows.
Hydrological hazards Hazards caused by the movement of water on land. Floodings.
Atmospheric hazards Hazards caused by the weather. Tropical storms, Sandstorms, Droughts.
Hazard risk: The probability or likelihood that a natural hazard may take place and affect a population. It is
dependant on the population’s exposure to (frequency) and vulnerability to (lacking management resources) the
hazard.
Factors Affecting Hazard Risk:
Wealth TIB poverty forces populations to live in unsafe housing with less access to healthcare,
investments, technologies, and services, which increase hazard risk.
Population TIB the increase demand for housing increases the population densities of unsafe but cheaper
Growth areas. If the area is high risk, it increases death toll per area, so increased hazard risk.
Urbanisation TIB there are many buildings in urban areas which can collapse and increase hazard risk.
Land Use TIB areas near natural hazards (floodplains, volcanos) have desirable features (fertile soil), so there
can be more infrastructure and people near these areas as a result of benefits over costs.
Climate TIB intensity and frequency increase in already affected areas, and distribution also spreads across
Change the globe.
Government TIB corrupted government may deny investments that would have lowered the natural risk.
Age/ Health TIB older/ weaker populations are more able to receive injuries than working/ healthy
populations.
Tectonic Hazards: A natural hazard caused by movement of tectonic plates (including volcanoes and earthquakes).
Tectonic plate: A rigid segment of the Earth’s crust which moves across the heavier, semi-molten rock below.
Layer State Material Thickness Avg Temperature
Crust Solid Rock 75km 20 degrees
Mantle Liquid Molten rock 2800km 2000 degrees
Outer Core Liquid Iron and Nickel 2200km 3700 degrees
Inner Core Solid Iron and Nickel 1200km 5500 degrees
Oceanic Crust Continental Crust
Newer Older
Sinks Cannot sink
Can be destroyed Cannot be destroyed
Denser Less Dense
Thin Thick
Convention Currents: The process which causes the movement of plates due to the movement of liquid magma in
the earth’s mantle caused by the core’s heat.
1. The outer core heats up the magma in the mantle.
2. The magma becomes less dense than its surroundings and rises upwards.
3. As it rises, it cools, solidifies, and drags the plates in the crust above.
4. The magma becomes less dense than its surroundings and sinks downwards.
5. It is reheated and the process repeats itself repeatedly.
Slab pull: Occurs when older, denser tectonic plates sink into the mantle, pulling newer and less dense sections of
plate along behind. Sinking in one place leads to plates moving apart in other places. Ridge push: new crust formed
at divergent plate margins is less dense than the surrounding crust and so it rises to form oceanic ridges. The older
, seafloor either side of the ridge slides away and this moves the seafloor apart – moving the tectonic plates. The
theory of continental drift: fossil records, similar rock geology, and corresponding coasts fit like jigsaw puzzles.
The Global Distribution of Tectonic Hazards occur on linear patterns on Plate Margins (the margin between two
tectonic plates with intense seismic activity) because of convection currents. The ring of fire is located in the Pacific
Ocean and has high tectonic activity. Hotspots: an area over a mantle plume where magma is hotter than
surrounding magma, resulting in the melting and thinning of the crust above, causing volcanic activity. Unlike
earthquakes, volcanic activity can only occur when there is a path for magma to travel to the surface of earth’s crust.
Earthquake: A sudden or violent movement within the Earth’s crust followed by a series of shocks. Volcano: An
opening in the Earth’s crust from which lava, ash and gases erupt.
Constructive plate margin Tectonic plate margin where rising magma adds new material to plates that are
e.g. The Mid-Atlantic diverging or moving apart.
Ridge 1. Convection currents cause plates move apart from each other.
2. Magma forces its way up through the gap in the crust.
3. As the lava cools and solidifies, new land is created. This process repeats and
forms many layers of rock which form volcanic islands. A (shield) volcano is
formed when the layer of rock is above sea level. They can also form rift
valleys on continental crust.
4. A volcanic eruption can happen above land. Additionally, earthquakes can
occur due to plate movements.
Destructive plate margin Tectonic plate margin where two plates are converging or coming together and
e.g. Between the Pacific oceanic plate is subducted. It can be associated with violent earthquakes and
and Eurasian plate. explosive volcanoes.
1. Convection currents cause plates to move towards each other.
2. The denser, heavier oceanic plate subducts under the continental plate,
leaving a deep ocean trench.
3. The oceanic crust is pulled into the mantle and melts into new magma,
causing pressure to build up under the crust around the subduction zone.
4. Eventually, the magma forces its way up through the weaknesses in the
continental crust. Once reached the surface, violent volcanic eruptions occur
in composite volcanoes.
5. They are less frequent because of years and years of increasing pressure.
Conservative plate margin Tectonic plate margin where two tectonic plates slide past each other.
1. Parallel plates move past each other in different directions or at different
speeds. Friction is built between the plates.
2. Part of the plate gets caught due to the rocky surface.
3. Over many years the build-up of friction causes pressure to build, until the
plates slide past in a sudden jolt where pressure ruptures.
4. An earthquake then occurs due to huge amounts of energy being released
from the focus (the exact point where pressure is ruptured in the curst) in the
form of shockwaves/ seismic waves which shake the ground at the epicentre
(the point directly above the focus on the crust surface.
5. They can result in tsunamis on oceanic margins and fault lines on continental
margins. No volcanoes since no magma can be released.
Collision plate margin When two continental plates move towards each other, neither can subduct, so
pressure accumulates amongst them creating fold mountains. E.g. the Himalayas.
The Richter scale (0-9): scale that measures the energy waves emitted by an earthquake (magnitude) by a
seismometer. It is logarithmic: ascending magnitudes are x10 more powerful. The Mercalli scale (0-12): scale based
on observation of words, pictures and accounts of eyewitnesses. It may not be reliable.
Primary effects: The initial impact of a natural event on people and property, caused directly by it, for instance the
ground buildings collapsing following an earthquake. Secondary effects: The after-effects that occur as indirect
impacts of a natural event, sometimes on a longer timescale, for instance fires due to ruptured gas mains resulting
from the ground shaking. Immediate responses: The reaction of people as the disaster happens and in the
