Lecture 4: Hazard management, monitoring and risk assessment Flashcards
What are the main causes of death from volcanoes
20th Century: ~96,000 deaths due to volcanic
eruptions
91% of the fatalities resulted from:
* Pyroclastic flows
* Lahars
* Tsunamis (volcanic)
* Famine and epidemic disease
What are the elements for assessing volcanic hazard
- volcano type
- crater lake or ice/snow cap presence
Pyroclastic flow hazard - Lahar hazard
- Lava flow hazard
- Number of subfeatures
- Maximum VEI
- Eruption frequency
Short-term forecasting and monitoring volcanoes
Short-term
* Volcano monitoring in real-time
* Eruption forecasting and prediction
* Volcanic emergency management and planning which involves government and local authorities, civil defence, park and forest service
Long term forecasting and monitoring volcanic eruptions
Long-term
* Identification of high-risk volcanoes
* Mapping and identifying past volcanic hazards to prepare a volcanic hazard map
* Long-term forecasts
Which of the active or dormant volcanoes that have erupted in the last 10,000 years are considered high risk?
Assessment based on:
* Past eruptive history
* Prevalence of explosive eruptions
* Evidence for seismic activity or ground deformation (changes in tilt, height, distance)
* Proximity to population
how do you monitor a volcano?
Volcano Monitoring:
Seismic Monitoring
Ground Deformation
Microgravity
Magnetic Field
Volcanic Gases
Temperature
Hydrology
explain Volcanic seismicity
- Volcanic eruptions are commonly preceded by Earth tremors, indicating a link between seismicity and eruptive activity
- When magma and volcanic gases and fluid move, they will cause rock to break or cracks to vibrate
- Breaking rocks cause high-frequency earthquakes
- Crack vibration either causes low-frequency earthquakes or a continuous tremor
Volcanic-related earthquakes
are generally < mag. 2 or 3 - Volcanic-related earthquakes
occur < 10 km beneath
volcano. - Earthquakes tend to occur in
swarms (up to hundreds of
events). - Networks of seismometers are
used to record volcanic-related
earthquakes.
seismic monitoring
- Networks of seismometers located on the volcano surface provide
information on the timing, location, depth and magnitude of tremors.
Tremors of short period –high frequency = fractures due to active intrusion or expansion of magma chamber.
Harmonic Tremors (due to
continuous vibration) = magma flowing through
feeder conduits.
Seismic signatures
- Different events that can cause ground to
vibrate at volcanoes - Each event has specific overall shape,
defined by amplitude (i.e. height of wave
form), and duration (i.e. length of
waveform).
What did Dvorak (1992) do?
Dvorak (1992), seismic monitoring, showed that
the magma chamber beneath the summit of a volcano acts as a reservoir of magma before dispatching to sites of eruption.
What is ground deformation?
Changes (deformation) to the surface of volcano can provide information about what is happening below the surface.
Detection of volcano deformation requires precise surveying
techniques.
What is inflation (ground deformation)
Inflation of a ground surface volcano is gradual and can occur over
a period of months and years
What is deflation
Deflation of ground surface of a volcano is sudden as the magma
chamber is emptied associated with
eruption.
Name some ground deformation monitoring techniques
Geodetic levelling
cGPS (Continuous Global Position System)
Tiltmeter
InSAR (Interferometric Synthetic Aperture Radar)
EDM (electronic distance meter)
What is geodetic levelling
- measures elevation differences between benchmarks
- by repeating surveys, elevation changes with time are recorded
