A. Monitoring of Earthquakes and Volcanoes Flashcards
By which categories are hazards classified?
Hazards are usually classified by:
- Cause
- Magnitude
- Frequency
- Speed of onset / length of warning
- Spatial concentration / dispersion
- Area extent
- Temporal spacing (regular or random)
What is typically measured to monitor a volcano?
- Remote satellite sensors detect ground surface and temperature changes caused by earth heating prior to eruption.
- Gravity meters on the ground detect gravitational changes due to magma movements.
- Geochemical changes are observed e.g. an increase in CO2, H2 and He may be seen in thermal waters or an increase in sulphur levels
- Cone bulges where upwelling magma swells the flanks of the volcano
What processes / changes are inspected to monitor earthquakes?
- Horizontal movements detected by measuring time taken by a laser to move between two points either side of a vault.
- Changes in Earth’s slope detected using a tilt meter (similar to a spirit level)
- Seismograph levels - small earthquakes indicate a larger one is on the way!
- Variations in Earth’s magnetic field
- Radon gas monitoring (could increase before earthquake)
- Seismic gap theory (is an earthquake expected?)
How does seismic gap theory work?
Geologists work out where a strong earthquake is likely to occur based on identifying where active faults have not been experiencing earthquakes for a long time e.g. 1989 San Francisco Bay Earthquake
What are the challenges facing prediction and monitoring?
- Always involves an element of risk
- Earthquakes give little warning before they strike (volcanoes are more obvious)
- False predictions are expensive and reduce people’s trust in the prediction system.
Which forms of environmental control were used for the Heimaey, Iceland, 1973 and Zafferana, Italy, 1992 eruptions (respectively)?
Heimaey, 1973: Cold water hosed on lava flow to prevent port being lost
Zafferana 1992: Earth walls used to contain lava, and lava flows were bombed to divert lava away from settlement
Which environmental controls can be used to reduce the effects of a volcanic eruption?
Other environmental controls include:
- Dynamite
- Earth dams / walls built to contain lava
- Construction of lava channels
- Embankments (to prevent future jökullhlaups from reaching an area - water)
Which responses generally reduce losses from natural disasters?
- Immediate short-term rescue efforts
- Followed by relief efforts which focus on food, shelter, water and sanitation
- Long-term reconstruction
- Insurance $$$ can help recovery
Which features do shops near the summit of Etna have to reduce their chance of economic losses / destruction?
- Light
- Mobile - moved downhill in case of eruption
- Pitched roofs - reduce the buildup of ash
- Single-storey - easier to move
List some features of aseismic design:
- Computer controlled weights on top of roof to reduce movement
- Birdcage interlocking steel frame which can sway during earth movements
- Open areas where people can assemble if evacuated and roads for quick access for emergency serivces
- Fire-resistant building materials
- Foundations stuck into bedrock with rubber shock absorbers to absorb earth tremors
How does community preparedness reduce earthquake losses?
Increasing risk perception:
Earthquake drills - 1st September is Earthquake Awareness Day in Japan
- Evacuation points placed in each neighbourhood
- Government information on how to improve safety features
- Gas supplies shut off immediately - reduce risk of fire
- People encouraged to keep survival pack near an exit and have enough food for three days
How does land use planning / zoning mitigate losses from earthquakes?
- Oil station depots are positioned away from homes and built on solid rock
- Land liable to liquefy is left for playing fields and nature reserves whilst homes are built on solid rock.
Why is hazard mapping carried out?
Hazard mapping is undertaken to identify:
- Areas that might liquefy
- Fault locations
- Dates of past movements
- Where landslides and tsunamis may occur
Did GeoNet (seismic monitoring agency in NZ) monitor White Island correctly in 2019?
White Island, NZ - one of most heavily monitored volcanoes in the world due to frequent release of volcanic gas.
- Phreatic eruption in December 2019 caught scientists by surprise and killed 24 people
GeoNet had raised the alert level for White Island from 1 to 2 in November 2019, but also recieved some criticism for the losses.
Why was it arguably unfair to criticise GeoNet for the losses from the 2019 White Island eruption?
GeoNet had raised the alert level of the volcano to Level 2 - eruption at any time.
Phreatic eruptions are also difficult to predict exactly as their causes are currently poorly understood.
GeoNet’s warning had been ignored - the island is privately owned, and tour companies can make their own decision on how safe it is - tour company criticised.
