IB Geography: Geophysical Hazards Vocab
45 flashcards · Other · by Gabrielle Wong
Hazard: Threat with the potential to cause loss of life, injury, damage, or environmental degradation
Loose rocks are an example of a hazard.
Hazard Event: Occurrence of a hazard and the effects that change the demographic/economic/environmental conditions of a community
Earthquakes are hazard events.
Disaster: Major hazard event – causes widespread disruption with impacts a community isn’t able to deal with independently
Earthquakes like the 2010 Haiti Earthquake are disasters in part because of the poor infrastructure and programs in place to deal with them.
Risk: Probability of a hazard event causing harm
The risk of some mass movements, such as soil creep, isn’t very high, especially compared to faster and more wet mass movements such as a mudslide.
Vulnerability: Conditions that increase susceptibility to a hazard/event’s impacts
Those who lack their own transportation are much more vulnerable to a hazard event because their capacity to quickly escape has been reduced.
Hazard Perception: The degree to which people consider a hazard a threat
People living in Malin before the mudslide had very poor hazard perception because they were unaware that their farming and mining activity was increasing the risk of a mass movement.
Secondary Risk: Indirect effects of a hazard event
The hazardous nature of a flood caused by burst pipes from an earthquake is a secondary hazard of the earthquake.
Reselience: ability to protect lives and buildings from destruction and to recover from a hazard event
The resilience of a community to earthquakes can be increased through improved buildings, education, and individual preparedness. Japan has done a good job of increasing its reselience; ex. though building codes that allow for far less drift, the installation of shock absorbers in buildings etc.
Adaption: alteration of human activities to account for risk
Humans have adapted for the possibility of a mass movement by installing retaining walls and rock traps in areas with steep slopes.
Lithosphere: top layer crust of the earth
The lithosphere is made of lighter continental crust and more dense oceanic crust.
Mesosphere: more dense middle of the earth
The mesosphere is between the lithosphere and centrosphere.
Asthenosphere: top layer of the mesosphere, partially molten and plastic
Convection currents, which are responsible for the movement of plates on the earth, are found in the asthenosphere.
Convection currents: Movement of less dense, hotter material up, which eventually cools and is pushed back down, leading to the transfer of heat to the surface as well Movement of crust is caused when the convection currents rotate the other way from each other
Convection currents are sometimes responsible for the movement of plates.
Centrosphere: extremely hot center of the earth, radiates heat (made of an outer and inner core)
The high heat and pressure on the centrosphere leads to the radiation of heat from it, which warms the earth and is the mechanism behind convection currents in the asthenosphere.
Continential drift: The concept that all continents used to be part of one large continental mass (commonly called Pangea)
Evidence for the theory of continental drift includes coastline fit (observation that continent coastlines fit together and would form one coherent piece if placed next to each other), geologic fit (the similarity of rocks) and paleoclimatology (finding similar ice cores and fossils in different continents)
Diverging plate boundaries: Plate movement in which two plates are moving away from each other, leading to the formation of new land (magma cools and becomes crust), which is why they are also called constructive plate margins.
Diverging plate boundaries form ocean ridges and rifts, such as the African Rift Valley. They are associated with earthquake and volcanic activity. · Spreading can create transform faults = earthquakes · Often the less destructive volcanoes = magma is able to freely flow out, doesn’t get stuck · Formation of basaltic lava plains · But is sometimes associated with larger volcanoes ex. Mount Kilimanjaro in the East African Rift Valley
Converging plate boundaries (aka destructive plate margins): Plate movement in which two plates are moving closer to each other; the result depends on whether ocean and/or continental curst is involved. Ocean-ocean = chains of islands Continent-continent = fold mountains Ocean-continent = subduction zone
Converging plate boundaries are often associated with volcanic activity, earthquakes, and other hazard events. Subduction zones can cause major earthquakes as plates get stuck when sliding Formation of composite cones because material gets pushed back up to the surface
Subduction zone: Result of a converging plate boundary between oceanic and continental crust because the denser ocean crust is forced beneath the lighter crust. Composite cone volcano formation is also common because of the material being pushed back up.
There is a subduction zone on BC’s coastline – the Juan de Fuca Plate, which is why BC is at risk for an earthquake.
Transform faults: Plate movement in which two plates are sliding past each other (this often causes great friction)
Transform faults can lead to major earthquakes, which often occurs along California’s coast due to the San Andreas fault.
Shield volcano: Type of volcano with gentle slopes and wide bases, which form because their lava (basaltic lava) is very runny. Explosions typically aren’t violent.
Shield volcanos often form at diverging plate boundaries in the ocean or over hotspots/plumes (ex. Hawaii).
Cinder cone volcano: Type of smaller volcano made of pyroclastic flow (layers of cinder/ash); the lava of these volcanos is andesitic lava, which is sticky and thick.
Cinder cone volcanos often form on continents, and they aren’t as tall. (the largest is 3350 m in Guatemala, but most are under 300 m)
Composite cone volcano: Type of volcano that is tall and symmetrical; steeper than shield cones but less steep than cinder cones. Made of layers of lava and ash, with andesitic lava that leads to dangerous explosions.
Composite cone volcanos are dangerous because they have andesitic lava which creates a plug (pressure builds = more violent explosion) and they are often tall, meaning the hot lava mixes with snow, creating lahar.
Lahar: flow of lava mixed with mud and water
Lahar is very dangerous, and forms due to the mixture of melting snow on a composite cone volcano and lava due to the heat of an eruption.
Volcanic Explosivity Index: Method to measure severity of volcanic eruption based on volume of erupted lava. (amount of material released)
The largest eruption has been given a VEI of 8. (Wah Wah Springs millions of years ago)
Lava eruption: Eruption of lava that is typically runny ex. Lots of basaltic lava from a fissure in Iceland building to vast plateaus
Low viscosity lava is less dangerous because it is able to erupt frequently, reducing build-up of pressure and therefore strength of explosion.
Pyroclastic eruption: Eruption including ash/rock flow, occurring due to the build-up of pressure because sticky lava forms a plug
Mt St Helens was a pyroclastic eruption.
Earthquake: Defined as the shaking or seismic waves that occur when stress-deformed rocks break or release pressure due to elastic rebound
Earthquakes can occur due to the movement of plates (ex. Transform faults), but can also be the result of a volcanic eruption, an isostatic readjustment, or the sinking of the ground due to removal of groundwater
Focus: exact point below the earth’s surface where the rock fracture occurs
Epicenter: Point at the surface where earthquake is first felt (also the strongest)
Richter scale: Most common method used by general public for measuring the strength of an earthquake; a logarithmic scale, but doesn’t consider the length of the quake
Moment magnitude scale: Another method of measuring earthquakes that looks at a measure of an earthquake's magnitude based on its seismic moment - length and shaking
Mercali scale: A more visual method of measuring earthquakes based on level of damage observed
Primary (compression) wave: The first and fastest kind of wave a seismograph will detect; travels by compressing and expanding the ground it moves through
Secondary (shear) wave: Travels slower and pushes the ground in a side to side motion
Surface wave: Occurs when these waves reach the surface, shaking the ground and causing damage characteristic of earthquakes (love=sideways, Rayleigh = up/down)
The impacts of an earthquake can include liquefication of land, destruction of buildings, tsunamis etc. Japan has built up high resiliency to earthquakes because of their high frequency.
Earthquake-proof building: Refers to measures that can be taken to increase a buildings’ resilience to an earthquake including a soft story (something for the building to collapse into), basement isolation (reduces shaking of upper areas), deeper foundations, steel frames, and shorter structures
Japan has built up high resiliency to earthquakes because of their high frequency.
Mass movement: large scale movements of the earth’s surface that are not accompanied by a moving agent
Earthquakes ARE NOT mass movements!
Pore pressure: Concept that water lubricates and fills the holes within a surface, increasing its volume and pushing it out (common trigger for a mass movement)
Many mass movements are caused by heavy rainfall because it increases the stress on the slope.
Shear strength and shear stress: The competing factors on a slope that determine whether it will collapse (mass movement) or not
A mass movement such as a landslide or slump is very likely to occur when shear stress overwhelms shear strength
Hotspot: also called a plume, especially hot area of crust from which volcano and earthquake activity can be detected
Hawaii is an example of a hotspot.
The structuralist model states that people live in high-risk areas because the structure around them forces them to do so.
Ex. people live in Haiti despite the fact that it is at high risk for violent, dangerous earthquakes, because they feel like they don't have any other choice
Rescue: search and rescue activities, occur in the hours/days after
First stage of recovery from a natural disaster
Rehabilitation: restoring services, building of temporary structures ex. field hospials
Second stage of recovery from a natural disaster
Reconstruction: rebuilding of what was destroyed, ideally with improvements
Third stage of recovery from a natural disaster