Week 8, Volcanos and Tsunamis

Question 1

How can we reduce volcanic risks?

Answer 1

• Identify risk areas: hazard maps
• Monitor volcanic activity: define normal vs significantly changed behaviour
• Develop emergency plan

Question 2

What do scientists monitor in terms of volcanic activity?

Answer 2

Seismicity
Gas emissions
Ground deformation
Ground temperature

Question 3

4 types of volcanic seismicity

Answer 3

• 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

Question 4

What’s an example of risk reduction success?

Answer 4

Mt. Pinatubo 1991

Question 5

Why is there concern regarding volcanic risks around Mt. Meager?

Answer 5

If glaciers completely melt, how does that effect the pressure on the magma chamber?

Question 6

Fumaroles

Answer 6

A hole in a glacier excreting toxic gasses…

Sulfur dioxide and hydrogen sulfide

Question 7

Tsunami stages

Answer 7

1. Generation
2. Propogation
3. Inundation

Question 8

Tsunami

Answer 8

A series of long period ocean waves caused by wave displacement from an impulsive event.

Not a tidal wave.

Japanese. Tsu: harbour, Nami: wave.

Question 9

Most earthquake tsunamis are a result of

Answer 9

a megathrust earthquake. (coseismic period)

Question 10

How does a caldera collapse cause a tsunami?

Answer 10

Volcano collapses into itself and displaces water.

Question 11

How do pyroclastic flows cause a tsunami?

Answer 11

Eruption produces pyroclastic flow that go into the ocean.

Question 12

How do underwater eruptions cause a tsunami?

Answer 12

Explosive eruptions at subduction zones.

Water vaporizing on contact with magma chamber causes a big explosion.

Question 13

How do landslides cause a tsunami?

Answer 13

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.

Question 14

Tsunami Period

Answer 14

Length of time between 2 tsunamis

Question 15

Tsunami Wave Peak

Answer 15

Water rises

Question 16

Tsunami Wave Trough

Answer 16

Water recedes

Question 17

Sea surface waves propogate _____ _____ motion, opposite of rayleigh waves.

Answer 17

Sea surface waves propogate elliptic particle motion, opposite of rayleigh waves.

Question 18

For deep water waves, is particle motion affected by the sea floor?

Answer 18

No.

Question 19

For shallow water waves, is particle motion affected by the sea floor?

Answer 19

Yes.

Question 20

Particle motion depends on

Answer 20

wavelength.

Question 21

Tsunamis act as ______ even in deep ocean. Explain how this is possible.

Answer 21

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.

Question 22

Tsunamis have a ___ amplitude and ___ period/wavelength.

Answer 22

Tsunamis have a small amplitude and a long period/wavelength.

Question 23

Tsunami wave energy is proportional to

Answer 23

amplitude(velocity)

Question 24

Tsnumai velocity is

Answer 24

dependant on relation to seabed. The wave slows down as it gets to shore and the amplitude dramatically increases. This conserves energy.

Question 25

Love waves are

Answer 25

transverse

Question 26

Compressional waves are

Answer 26

longitudinal

Question 27

Wave Focusing

Answer 27

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.

Question 28

Tsunami reverberation

Answer 28

Echoes of a tsunami in a bay, lengthy processes.

Can cause damage many hours later.