Geological Natural Disasters
At which type of plate boundary do two tectonic plates move apart?
A divergent plate boundary.
What type of volcanic eruption produces relatively fluid lava flows?
An effusive eruption.
Which volcanic eruption is a major case study for the effects of volcanic eruptions on climate?
Mount Pinatubo, which erupted in 1991.
What is an East Coast Low?
An intense low-pressure weather system that develops near Australia's east coast and can produce heavy rainfall, strong winds, flooding and coastal erosion.
What technology is used to detect and record earthquake vibrations?
A seismometer (or seismograph).
What is the point inside Earth where an earthquake begins called?
The focus, or hypocentre.
What volcanic hazard consists of a fast-moving mixture of water, ash, rock and volcanic debris?
A lahar.
What volcanic gas can contribute to short-term global cooling when it forms sulfate aerosols in the atmosphere?
Sulfur dioxide (SO₂).
What is one major ecological consequence of drought?
Reduced water availability can cause vegetation loss, reduced food availability, habitat degradation and increased stress or mortality in organisms.
Name one technology used to monitor changes in a volcano before an eruption.
Seismic monitoring, GPS, satellite/InSAR ground-movement monitoring, gas monitoring or ground-deformation measurements.
Why are earthquakes at divergent boundaries generally shallow?
Divergent boundaries involve relatively shallow crustal movement and faulting, so earthquake foci generally occur close to Earth's surface.
How can an undersea earthquake generate a tsunami?
If the earthquake causes sudden vertical displacement of the seafloor, it displaces the overlying water and generates a series of waves.
Why can an explosive volcanic eruption have a greater atmospheric impact than an effusive eruption?
Explosive eruptions can inject large amounts of ash and sulfur dioxide high into the atmosphere. Sulfur dioxide can form sulfate aerosols that reflect incoming solar radiation, causing temporary cooling.
How can human activities increase the risk or severity of flooding?
Activities such as urbanisation, vegetation removal and development on floodplains can increase surface runoff and reduce the land's ability to absorb water.
Why are earthquakes much more difficult to predict accurately than volcanic eruptions?
Volcanic eruptions often produce detectable warning signs such as increased seismic activity, ground deformation and gas emissions. Earthquakes generally provide no consistently reliable short-term warning signs.
Why are explosive volcanic eruptions generally associated with high-viscosity magma?
High-viscosity magma does not allow gases to escape easily. Gas becomes trapped, pressure builds and can produce an explosive eruption.
Compare the magma associated with an effusive eruption with the magma associated with an explosive eruption.
Effusive eruptions are generally associated with low-viscosity, low-silica basaltic magma, allowing gases to escape easily. Explosive eruptions are generally associated with more viscous, higher-silica magma that traps gases and allows pressure to build.
Explain how a bushfire can affect both the biotic and abiotic components of an ecosystem.
It can kill or displace organisms and destroy vegetation and habitat (biotic impacts), while also altering soil properties, nutrient cycling, air quality, erosion and water quality (abiotic impacts).
How can human activities increase the frequency or severity of bushfires?
Human-caused climate change can increase heat and dryness in many regions, while activities such as land clearing, accidental ignitions and inappropriate land management can also influence fire risk and severity.
How can building codes reduce the impact of earthquakes even though they cannot prevent earthquakes from occurring?
Building codes require structures to be designed to withstand earthquake forces, reducing structural failure, damage and the risk of injury or death.
Explain how the depth of earthquake foci changes along a subduction zone and why this occurs.
Earthquake foci become progressively deeper away from the trench as the oceanic plate descends beneath the other plate. Earthquakes can therefore occur from shallow depths near the boundary to much greater depths within the subducting slab, forming a Wadati–Benioff zone.
A magnitude 8 earthquake occurs beneath the ocean but causes little damage and no deaths. A magnitude 6 earthquake occurs beneath a densely populated city and causes widespread destruction. Explain why the second event could be considered the greater disaster.
Magnitude measures the energy released by the earthquake, but a disaster depends on the impact on people, infrastructure and the environment. The magnitude 6 earthquake has greater exposure and vulnerability because it affects a densely populated area, resulting in greater consequences.
Explain how Mount Pinatubo's 1991 eruption caused temporary global cooling.
The eruption released large quantities of sulfur dioxide into the atmosphere. The SO₂ formed sulfate aerosols in the stratosphere, which reflected some incoming solar radiation back to space. This reduced the amount of energy reaching Earth's surface and caused temporary global cooling.
Explain how human activities can increase the risk of landslides.
Vegetation removal can reduce root reinforcement of soil, while road construction, excavation and changes to drainage can destabilise slopes. Heavy rainfall can then trigger movement of the weakened slope.
A weather forecasting system predicts that an East Coast Low is likely to produce severe rainfall and damaging winds in three days. Explain how meteorological technology can help minimise its impacts.
Weather satellites, radar, weather stations and computer models can monitor atmospheric conditions and predict the system's movement and intensity. Authorities can issue warnings, close dangerous areas, prepare emergency services and allow communities to evacuate or protect infrastructure before the event occurs.