Week 7 Flashcards
1
Q
What are the hazards without eruption
A
- Groundshaking
- Fractures/ fissures
- Outgassing
- Acid Lakes
- Lahars and Landslides
2
Q
What is ground shaking
A
- Active volcanoes often exhibit seismicity associated with the movement of magma beneath the earth’s surface
- most volcanic seismicity consists of earthquakes of magnitude <3
- only rarely are volcanic earthquakes as large as M5-6
3
Q
What are fractures and fissures
A
produced by a slower process by the volcanic system
4
Q
Outgassing
A
- volcanoes often leak gas
- the gas may stay in the soil or percolate into the air
- CO2 is more dense than air, so it sits near the ground level.
- Animals (including people) can suffocate due to the concentrations of this odorless gas
- Although leaves of plants produce oxygen (O2) from CO2 during photosynthesis, their roots need to absorb O2 directly
- High CO2 concentrations in the soil kill plants by denying their roots O2 and interfering with nutrient uptake
5
Q
Acid Lakes
A
- Crater lakes can have pH values as low as 0.1 (very strong acid)
- This is the result of gases from magma, like CO2, SO2, HS, HCl and HF, dissolving in water
6
Q
Lahars and Landslides
A
- A lahar is a volcanic mudslide: mixture of water, rock fragments, soil and etc, flowing down a volcanic slope or a river valley on or near a volcano
- Lahars grow a they flow and erode material on the volcanic slopes
- Lahars can be triggered by eruption or by heavy rain
- ## they can move at 10s of meters per second and destroy communities
7
Q
What are the direct hazards with eruption
A
- Lava flows
- Pyroclastic flows
- Pyroclastic falls (ash fall)
- Groundshaking
- Fissuring
- Outgassing
- Lahars and Landslides
8
Q
Lava flows
A
- least hazardous of all processes in volcanic eruptions
- rate and distance depends on temperature, silica content, extrusion rate, and slope of the land
- cold lava flows with high silica content will not travel far due to high viscosity
- Biggest hazard is to property
9
Q
Pyroclastic
A
- Pyro: fire
- Clastic: broken
- Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases moving away from an erupting vent
10
Q
Pyroclastic flow
A
- pyroclastic flows destroy almost everything in their path
- they usually move faster than 80 km/hr, and have temperatures between 200 and 700 degrees C
- They can block streams and create temporary dams, that will later overtop and cause sudden flooding downstream
11
Q
Pyroclastic falls (ash fall)
A
- volcanic ash is composed of small fragments of rock
- the ash can cover wide areas and travel downwind from the erupting volcano
- reduce visibility: block sunlight
- damages engines
- dense: can collapse roofs
- disrupts power generation, transmission, and distribution
- clogs water supplies
-causes breathing difficulty - damages crops
12
Q
Landslides and tsunamis
A
- Sector collapse
- tsunami
- Change of topography/ bathymetry due to eruptions
13
Q
Indirect hazards with eruption
A
- air travel effects
- climate change
14
Q
Effect of volcanic ash on aircraft
A
- damage to jet engine
- abrasion to cockpit windows
- penetration of air conditioning system
- contamination of electrical, hydraulic and fuel systems
15
Q
Impact of cancelled flights
A
- Business and leisure travel delayed or canceled
- perishable goods lost
- industrial plants suspended production
16
Q
Climate change
A
- volcanic ash can physically block sunlight
- Pinatubo eruption (1991): global temp dropped by 0.5 degrees in 1991 - 1993
- Mt Tambora eruption (1815): global temperatures dropped by 0.4-9,7 degrees for three years
- ‘optical death’ - a measure of SO2
- impact of other erupted materials
- hotter summers
17
Q
What is a super volcano
A
- any volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 km3
18
Q
Modern instruments
A
- have recorded the pressure waves and tsunamis
- the pressure wave could travel around the earth for multiple circles
19
Q
Known VEI 8 eruptions
A
- Taupo volcanic zone, New Zealand- 26,500 and 254,000 years ago
- Toba, Sumatra- 74,000 years ago
- Yellowstone - 640,000, 2,100,000, 4,500,000, 6,000,000 years ago
- Cerro Galan, Argentina - 2,500,000 years ago
- Pacana, Chile - 4,000,000 years ago
20
Q
Toba supereruption -74,000 years ago
A
- estimated 2,800 km3 of material
- pyroclastic floes over 20,000 km2
- ash deposits up to 600 m thick by the main vent
- up to 9 m of ash in Malaysia
- 15 cm of ash all over south asia
- resulting “volcanic winter” decreased global temperatures by 3-3.5 degrees for several years
- Probably few plants or animals in southeast asia survived
21
Q
What to do?
A
- Studies of historical events, to know what to plan for
- Volcano monitoring
1. Volcanic tremor- seismic signals indicating magma movement
2. Ground deformation (GPS, InSAR, Tiltmeter)
3. Gas monitoring - Infrasound
- Mapping the surface displacement from the space
22
Q
Gas monitoring
A
- Gas samples are collected from fumaroles and active vents
- Gas levels may also be monitored by remote sensing techniques
23
Q
Heat and hydrothermal activity
A
- Hydrothermal activity demonstrates presence of magma, not necessarily magma movement
- thermal features can be monitored by:
1. night aerial observations
2. Thermal (infrared) imaging
3. Direct temperature measurement
24
Q
Volcano mitgation
A
- unlike earthquakes, we often can predict volcanic eruptions and evacuate large population centers
- this requires careful monitoring, and willingness to accept false alarms
- we cannot prevent volcanic eruptions, and when they happen there will be large financial losses and human impact
- even when we successfully anticipate an eruption, we cannot always predict the style and severity
