Hazard 2: Geophysical Hazard Risks Flashcards
Where are volcanoes distributed?
Most volcanoes are found at plate boundaries. Some exceptions - Hawaii, which occur over hotspots.
75% of the Earth’s 550 historically active volcanoes lie along the Pacific Ring of Fire.
Other areas of active vulcanicity include Iceland, Montserrat and Mt Nyiragongo in the DRC.
Volcanic activity takes place at convergent boundaries, where one plate is subducted under another. If both plates are oceanic -submarine volcanoes erupt to produce island arcs, like that of the Aleutian Island Arc off Alaska. Continental & oceanic plates produces significant volcanic mountain ranges such as the Andes, which forms from the subducting Nazca plate under South America.
These are the result of high silicate magma rising upwards through the continental crust. Volcanoes also form at hotspots and divergent plate boundaries, where shield volcanoes are more common. Eg/ Mauna Loa
Where are earthquakes distributed?
Occur at all plate boundaries.
The oceanic fracture zone (OFZ) a belt of activity through the oceans along the mid-ocean ridges, coming ashore in Africa, the Red sea, the Dead sea rift and California.
The continental fracture zone (CFZ) a belt of activity following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies.
High frequency, low magnitude earthquakes are more associated with conservative plate boundaries such as the San Andreas Fault in California. These earthquakes tend to be shallow in nature and low magnitude but conservative boundaries can also produce much higher magnitude earthquakes but at lower frequency.
Where are landslides distributed?
Landslides can occur anywhere in the world but there is a higher risk in steep mountainous regions with coarse soil. Landslide risk is greatest in populated regions with high rainfall events, such as tropical storms and lead to slope saturation and river flooding. The map below shows that greater risk of landslides links closely to mountain regions. Western regions of the Americas, East Asia and South East Asia stand out as regions of high risk. In addition, regions experiencing population pressure, deforestation, road construction, mining and plantations all lead to greater risk of landslides.
How are earthquake magnitudes measured?
- Energy release is measured by the logarithmic moment magnitude scale (MMS)
- Damaging effects are measured by the Mercalli scale ( measures intensity of shaking)
How is volcano’s magnitude measured?
- Measured by the volcanic explosivity index ( VEI) and based on the volume, duration and column height of ejections.
- Can be related to the type of plate boundary the volcano is located on:
° Effusive eruptions of basaltic lavas with low VEI ( 0-3) are associated with constructive boundaries or plumes
° Explosive eruptions with high VEI (4 to 7) of andesitic or rhyolitic lava are associated with destructive boundaries.
What is the tsunami scale?
Why is recurrence intervals important when measuring risk assessment?
Understanding the importance of recurrence intervals is an important way of measuring risk and preparing for future management of hazards. Low recurrence intervals are often associated with relatively poor knowledge and management as well low levels of public perception of risk. Places that experience frequent hazards with high recurrence intervals tend to be better prepared and the public have a lived experience of hazards and so have greater perception of risk.
Geologists use recurrence intervals to create detailedseismic hazard curvesthat work on the basis of probability of an earthquake of a certain magnitude occurring in certain location. From these curveshazard probability mapscan be generated that help authorities plan hazard mitigation and responses both in the short term and long term.
Define: Hazard
Hazard = A threat ( natural or human) that has the potential to cause loss of life, injury, property damage, socio-economic disruption or environmental damage.
Define: Disaster
Disaster = A major hazard event that causes widespread disruption to an area and where the affected community is unable to deal adequately without outside help.
Define: Risk
Risk = The probability of a hazard event causing harmful consequences ( expected losses in terms of death, injuries, property damage, economy and environment).
Define: Vulnerability
Vulnerability = is the extent to which a community could be damaged or disrupted by a hazard.
How do you calculate risk?
(Hazard (H) X Vulnerability (V)) / Capacity to Cope (C)
The risk of a disaster increases as the frequency or severity of hazards increases, people’s vulnerability increases and people’s capacity to cope (ability to cope with the consequences) is decreased.
Why do people live in hazardous areas?
Three approaches:
- Fatalist approach
- Acceptance approach
- Adaptation approach
Define: Fatalist approach
Fatalist approach – ‘God’s will’, no alternative, losses accepted, Russian roulette – optimistic approach.
Define: Acceptance approach
Fatalist approach – ‘God’s will’, no alternative, losses accepted, Russian roulette – optimistic approach.
Define: Adaptation approach
Adaptation approach – Events can be prevented & early warnings given. The area has been made safer by technology, fewer people will be affected.
Why are women more vulnerable?
- Women are more home bound than men and so when hazards strike they are often the victims of collapsing buildings
- During tsunamis women have been impacted more -caring roles towards children and elderly and get caught up in their attempt to help family members whilst men are at work, are independent and so more able to make survival decisions.
-Oxfam survey - four times as many women than men were killed during the 2004 tsunami -men taught how to swim and climb trees at young ages, while women were not. - After the Haiti earthquake women were more vulnerable with rape on the rise.
Why was Haiti so at risk from earthquake? (Hazard)
Tectonics = earthquake ( transform boundary)
Geography = epicentre close to capital Port au Prince ( 25km away), focus shallow – only 13km, spatial extent quite large 120km2, hadn’t experience an earthquake in 150yrs, so no experience, Magnitude 7, speed of onset = sudden ( 30-60 seconds).
Why was Haiti so at risk from earthquake? (Vulnerability)
Living conditions = Buildings & infrastructure not earthquake proof, high unemployment, relied on informal sector, many lived in slums, 72% lived in poverty, homes built on slopes.
Pressures = rapid rural to urban migration, growth of slums..all put pressure on local authorities. Hillsides stripped of trees to make more space. Low HDI. Education levels are lower, so perception & risk low.
Causes = Poor governance - Basic needs were not being met – limited access to roads, electricity & sanitation. Poor planning – deforestation & building on hillsides, no preparedness, didn’t ensure correct building codes, corrupt government. Access to health care & education is poor. Low-income groups lack a ‘safety net’ after a disaster – personal one ( savings, food) or government one ( social security, aid, free healthcare)
What is the Pressure and Release (PAR) model?
What geographical factors can affect the geophysical hazard event impacts?
- Population density: highly populated areas may be hard to evacuate.
- Isolation & poor accessibility can slow rescue and relief
Degree of urbanisation:
Death tolls can be high in urban areas because of the concentration of at –risk people
Urban areas usually have more assets ( hospitals, food stores and transport systems) than rural areas, which increase resilience.
L’Aquila, Italy is 60km away from Rome, the Civil Defence was able to make a rapid response. - Timing: The L’Aquila 6.3 magnitude (Italy) earthquake in 2009 killed 308 & injured 1,500. It hit at 3:32am leaving people no chance to make quick decisions. However, if had occurred during school day 100s if not 1,000s could have been killed due to poor school infrastructure.
How does unequal access to education influence vulnerability and resilience?
How does unequal access to housing influence vulnerability and resilience?
How does unequal access to health care influence vulnerability and resilience?
How does urbanisation influence vulnerability and resilience?
How does unequal access to income opportunities influence vulnerability and resilience?
How does population density influence vulnerability and resilience?
How does governance influence vulnerability and resilience?
How does accessibility influence vulnerability and resilience?
What is an example where population density affected the impacts of a geophysical hazard?
Sulaweshi ( Indonesia) 7.5 mag earthquake in 2018
2nd Hazards – tsuanami – Town of Donnaggala is located on the low coastal plain and felt the full force of the waves. The town of Palu suffered from liquefaction and as it was located at the end of a coastal inlet, suffered the largest waves, as they were funnelled, gaining in height. Part of the town ended up flowing town hill due to liquefaction.
What are example where isolation affected the impacts of a geophysical hazard?
- Nepal 7.9 earthquake, April 2015
2nd hazards – caused an avalanche at Everest Base camp
District of Rasuwa – hospital located at 2,030m devastated – couldn’t use roads due to fears of landslides, had to shuttle supplies in on helicopters. - Greenland - landslide in a fjord in Nugaatsiaq led to a 90m tsunami, with 3 villages having to be evacuated. The capital Nuuk is 3,000km away – ltd roads, resources 7 difficult to access by boat made the response challenging.
