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hazardous environments - Coggle Diagram
hazardous environments
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plate boundaries
destructive
denser oceanic plate subducts into the mantle an dis destroyed. the melting plate is less dense than the surrounding mantle so rises to the surface to form volcanoes. A deep ocean trench is formed at the point of subduction
volcanoes, earthquakes, mountains and ocean trenches
constructive
as the 2 plates move apart, due to convection currents in the mantle, new magma rises from the mantle to fill the gap between them. it cools to create new crust and volcanoes
volcanoes, small earthquakes, ocean ridges
collision
the 2 plates meet head on, but are both the same density. this means no crust can be destroyed through subduction, so there are no volcanoes and the plates are pushed upwards
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conservative
2 plates move past each other in different direction, or the same direction at different speeds. crust isn't created or destroyed
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volcanoes
an opening or vent in the earth's surface through which molten material erupts and solidifies as lava
classification
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extinct
a volcano which has not erupted for many thousands or millions of years and not expected to erupt again
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molten rock originated in the mantle, powered by the Earth's inner heat. Driven by buoyancy and gas pressure magma is lighter than surrounding solid so forces its way upwards into magma chambers. this material accumulates and can exert pressure on the surface, forcing it to bulge upwards. Ultimately, the pressure gets so great that this magma breaks through zones of weaknesses in the Earth's crust, when an eruption begins
volcanic hazards
lava flows
hardly any people killed as slow moving and can be outrun, but can reach beyond 10 km but don't cause excessive damage
pyrochlastic flows
high density hot mix of lava, ash, pumice and gas can roll down the slopes of a volcano at terrifying speeds and temps over 300 C. Usually occur from the collapse of an eruption cloud that can't hold its own weight or the boiling over of an eruptive event from the crater. can also travel across water/flow underwater
ash/tephra
rock fragments that come from explosive volcanoes which can cover buildings, forests and farmland. less than 2mm in size and can be blown by winds for many miles. large accumulations can collapse roofs and burry homes. Tephra is larger so can't be blown so far
Gas emissions
silent volcanic killer as they roll down the slopes, displacing fresh air and is mainly CO2 as it is heavier than air, colourless and odourless as well as hydrogen sulfide
lahars
when volcanic rock mixes with water (often from melting ice) a debris called lahar develops. it is like flowing concrete and rolls down valleys around composite volcanoes. as they flow, the size increases and they can travel up to 100 km/h wiping out everything in their path
VEI
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however ash is not the main product of all eruptions, with some being less eruptive with lava instead
hotspot volcanoes
hot spot breaks through crust to form an island. Magma is less dense than surrounding rock so rises to the surface. The plate is in constant motion so the island will eventually move off the hot spot, making room for a second volcanic island. a third and fourth island forms as the plate continues to move over the hotspot
earthquakes
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features
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epicentre
on the surface of the earth, directly above the focus, where tremors are stongest
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measurement
richter
measures strength of earthquakes using a seismometer. it is a logarithmic scale, meaning 1 point up represents a 30 times increase in released energy. it focuses on energy released
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mercalli
measures effect of an earthquake using roman numerals (I-XII) and is based on peoples experiences making it subjective
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moment magnitude scale
the most recent scale, which is similar to the Richter, as it measures energy released but is based on rock movement along fault lines. it is the most accurate and reliable and can measure above 10 accurately
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management
prediction
attempts to forecast an event, where and when it will happen, based on current knowledge
seismic waves - seisometers can be used to pick up the vibrations in the earth's crust. an increase in vibrations may indicate a possible earthquake
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protection
it is the buildings that kill, not the earthquakes themselves
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earthquake resistant - can suffer some damage but shouldn't collapse. the aim is to make buildings stronger and more flexible, reinforcing concrete with steel or isolating foundation from ground both do this.
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tropical cyclones
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formation
warm air from thunderstorms and deep warm oceans (27C +) mix together and rise, creating an area of low pressure
the earths atmosphere trys to balance this, so air rushes in from surroundings, where pressure is higher, causing strong winds
due to coriolis effect, the winds spin upwards around the low pressure area. the eye is formed where warm air has risen and cooled air begins to sink
as it moves across the ocean, it picks up more moist air and the winds get stronger
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when it meets land, it isn't fuelled so it loses power and weakens
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Saffir-Simpon scale
based on wind speed, air pressure, storm surges and typical damage
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not exact and can be averaged, as well as not including the damage or duration
storm surges
low pressure creating a bulge in sea level. very strong winds move water towards coast. waves hit shorelines and sea beds. these cause high frequency causing mass destruction including floating debris as well as waves battering beaches.
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hazard management
prediction, preparation and response are all key factors of hazard management