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Summary Hazardous environments alevel geography notes
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High level hazardous environment Alevel Geography notes. Full spec notes and case studies. Easy to read and comprehensive.
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HazardsHazards refer to natural or human-induced events that pose a threat to human life, property, or the
environment. Impacts are the consequences of these hazards, which can include damage, loss of
life, economic disruption, environmental degradation, and social upheaval.
Disaster- a hazard that causes so much damage and injury that recovery without help is impossible.
Vulnerability- the degree to which conditions make a population more likely to experience a hazard
event, which they do not expect, cope with or recover from. Human attachment to property
increases vulnerability.
Resilience- how well a population recovers from a disaster.
Causes of hazards: -
tectonic. (geological) - earthquakes and volcanic eruptions
-geomorphological (processes acting on the land surface) - mass movements
-atmospheric (meteorological) - tropical cyclones and tornadoes
Classification of hazards:
-Magnitude, scale or size; some types have their own scales
- Frequency of occurrence
- Length of warning time - rapid onset hazards are much more dangerous than slow onset ones
- Spatial distribution.
,Hazards relating to tectonic processes
Earthquakes
Earthquakes occur on all types of plate boundary, at hot spots away from plate boundaries and at
fault lines. When two plates try and move but become stuck against each other, stress builds up.
Eventually, plates break free along a fault, causing a sudden release of pressure and energy and
releases seismic waves from the focus point, where rocks break.
Epicentre is the point on the earth’s surface immediately above the focus point.
Most earthquake foci occur in narrow zones along plate boundaries, but their effects extend far
beyond the plate boundary.
There are 4 types of seismic zones:
-Destructive (convergent) plate margins have shallow, intermediate and deep earthquakes.
(depending on where the focus is) They are inclined along the Benioff zone on the subducting plate
where slab pull occurs.
-Collision boundaries of two converging continental plates, such as between the Eurasian and Indian
plates where the Himalayas formed.
,-Conservative plate margins where faults, such as the San Andreas (between Pacific and North
American plates) in California, have earthquakes but no volcanic activity. Here the North American
and Pacific plates are moving side-by-side. Great friction builds up between the plates as they catch
against each other which is eventually released in very powerful earthquakes. usually from a
shallow focus.
- Constructive plate margins at mid-ocean ridges where ridge push (slab push) occurs. The
lithosphere is too weak and thin for a lot of stress to build up, so large earthquakes do not occur.
They are usually shallow focus and occur with volcanic activity.
Some powerful earthquakes may be non-tectonic, caused by human activity putting too much stress
on faults. The 7.9 magnitude earthquake in Sichuan, China, in 2008, which killed nearly 70,000
people, was linked to the construction of a reservoir, which added a very heavy weight of water to
the surface and rocks fractured.
No government preparation for this event and IX on Mercalli scale.
One major landslide at Beichuan County buried an entire town, while a landslide at Jian river,
formed a temporary landslide dam. This barrier eventually breached, releasing massive floods
downstream.
Strike slip faulting- conservative,
normal faulting- constructive, thrust
faulting- destructive
Earthquakes primary hazards
Earth faulting
, A rupture of the Earth's surface caused by an earthquake, where ground is pushed and pulled apart.
This is more common if there is a shallow focus along a pre-existing fault.
The 2011 Tohoku earthquake in Japan triggered significant surface faulting along the Pacific coast of
Tōhoku. 9.0 on the Richter scale and caused extensive damage, including subsidence and uplift along
the coastline. This faulting occurred due to the rupture of the Japan Trench subduction zone,
resulting in massive seismic activity and displacement along the fault line.
Shaking
Earthquakes send out seismic energy waves, which are recorded by seismographs. Primary (P) waves
travel fastest and arrive at a place first, followed by secondary (S) waves.
The slowest waves, surface waves, travel along the Earth's surface. Being long waves with large
amplitude, they cause most of the damage as they shake the ground most violently.
Seismograph records ground vibrations. Haiti, in the
Caribbean is vulnerable to natural disasters. It does not
have the proper infrastructure for a wide spread
convectional seismic measuring network. They don’t have
a fully functional power grid to power sensors. In the
aftermath of the quake in 2010, international organizations
provided financing to set up conventional seismometers. In
2021, the country had a singular seismometer at the US
embassy to gather data needed to identify the point where
rocks where breaking and future faults.
Secondary and Long seismic waves do not go through fluids. But Primary waves do.
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