Week 8, Volcanos and Tsunamis Flashcards
How can we reduce volcanic risks?
- Identify risk areas: hazard maps
- Monitor volcanic activity: define normal vs significantly changed behaviour
- Develop emergency plan
What do scientists monitor in terms of volcanic activity?
Seismicity
Gas emissions
Ground deformation
Ground temperature
4 types of volcanic seismicity
- Tectonic like earthquakes: deep earthquakes, no big deal, located away from volcano, high-frequency signatures, and sharp arrivals
- Shallow volcanic earthquakes: located under dome, depths less than 3km, medium to low frequency seismic arrivals
- Surface events: not a classic earthquake at all, rockfall or landslides, surface related processes, especially strata volcanos, complicated signatures, no clear beginning or end
- Harmonic tremors: long lasting, rhythmic, origin is not well understood, often associated with active volcanos
What’s an example of risk reduction success?
Mt. Pinatubo 1991
Why is there concern regarding volcanic risks around Mt. Meager?
If glaciers completely melt, how does that effect the pressure on the magma chamber?
Fumaroles
A hole in a glacier excreting toxic gasses…
Sulfur dioxide and hydrogen sulfide
Tsunami stages
- Generation
- Propogation
- Inundation
Tsunami
A series of long period ocean waves caused by wave displacement from an impulsive event.
Not a tidal wave.
Japanese. Tsu: harbour, Nami: wave.
Most earthquake tsunamis are a result of
a megathrust earthquake. (coseismic period)
How does a caldera collapse cause a tsunami?
Volcano collapses into itself and displaces water.
How do pyroclastic flows cause a tsunami?
Eruption produces pyroclastic flow that go into the ocean.
How do underwater eruptions cause a tsunami?
Explosive eruptions at subduction zones.
Water vaporizing on contact with magma chamber causes a big explosion.
How do landslides cause a tsunami?
This happens all the time.
Terrestrial landslide enters water, creates wave. OR. Underwater/submarine landslide or slump displaces water, slump would pull water with it.
Tsunami Period
Length of time between 2 tsunamis
Tsunami Wave Peak
Water rises
Tsunami Wave Trough
Water recedes
Sea surface waves propogate _____ _____ motion, opposite of rayleigh waves.
Sea surface waves propogate elliptic particle motion, opposite of rayleigh waves.
For deep water waves, is particle motion affected by the sea floor?
No.
For shallow water waves, is particle motion affected by the sea floor?
Yes.
Particle motion depends on
wavelength.
Tsunamis act as ______ even in deep ocean. Explain how this is possible.
Tsunamis act as shallow water waves even in deep ocean.
Tsunamis are so big that they experience interaction with the sea bed, so they are, in essence, shallow water waves.
Tsunamis have a ___ amplitude and ___ period/wavelength.
Tsunamis have a small amplitude and a long period/wavelength.
Tsunami wave energy is proportional to
amplitude(velocity)
Tsnumai velocity is
dependant on relation to seabed. The wave slows down as it gets to shore and the amplitude dramatically increases. This conserves energy.
Love waves are
transverse
Compressional waves are
longitudinal
Wave Focusing
Phenomenon observed by all waves, however this is a specific concern for tsunamis as they are so large and strong.
Wave energy focused (refracted) by shallow-water bathymetry.
Wave refracts to slower velocities, wave bends into that direction, deep water at centre of bay focuses on edges of bays.
Tsunami reverberation
Echoes of a tsunami in a bay, lengthy processes.
Can cause damage many hours later.
