Chapter #6 Flashcards
Tsunami Tigger’s include,
- Earthquakes
- Landslides
- Explosive volcanic eruptions
- Meteorite impacts
How are Tsunami’s generated?
The sudden movement of a large mass against the sea surface.
These masses include:
* the seafloor shifting up or down
* a submarine and/or subaerial landslide
* a pyroclastic flow
* an air blast from an explosive volcanic eruption
* a meteorite impact
Tsunamis are not _____
Tsunamis are not tidal waves or large storm waves
What creates the multiple waves in a Tsunami?
The equilibrium of the water is disrupted, either pushing water up or down, then the gravitational force attempts to restore equilibrium forming multiple waves.
Trough (Tsunami)
The line along which water depth is at it’s lowest
Crest (Tsunami)
The line along which water depth is at it’s highest
Tsunami wave characteristics depend on 3 variables, these are
- The area over which the generating mass moves
- The amount of movement
- The velocity of movement
Class Question #1
Why are tsunamis classified as gravity waves?
a) Gravity causes the seafloor to suddenly rise, pushing up the water’s
surface.
b) Gravity acts as a restoring force that returns water to its equilibrium
level.
c) Gravity differences between the seafloor and continental rock
create very high tsunami waves.
d) Gravity increases the complexity of tsunami waves as they
propagate across open oceans.
b) Gravity acts as a restoring force that returns water to its
equilibrium level. (correct answer)
Tsunami height variables include,
- The distance between source and location
- The amount of water pushed by mass
- The shape and velocity of the mass pushing the water
- wave reflection, refraction, and interference
Are tsunami waves faster near the shore or open sea?
They are faster at open sea
Velocity of Tsunami waves formula is
C = sqrt(gD)
Wave energy of Tsunami waves formula is
E = 0.125pgH^2L
Drawback (Tsunami)
When a approaching tsunami trough lowers at sea level
Tsunami Elevation
The greatest vertical distance from a crest and sea level
Inundation distance
The horizontal distance between the normal shore line and the inundation limit
Run-up elevation
The vertical distance from the normal shoreline to the inundation limit
Coast factors that increase wave height include,
- Sand bars due to shallow depth
- Bays and estuaries due to narrowing of wave energy focus
How many waves are in a train, and how long for the entire event
6 - 25 waves, 3-6 hours
Storm waves
- Limited drawback and inundation distance
- Wave period: 5 - 20 seconds
- Shallow wave base moves a small amount of water
Tsunamis
- Extensive drawback and inundation distance
- Wave period: 10 min - 2 hours
- Deep wave base moves a large volume of water
Tsunamis have more dynamic pressure due to faster velocity
Wind driven waves go how far? And their characteristics
Only make it to the beach, they are more narrow and carry a small volume of water in a single wave.
Characteristics of a Tsunami, and how far do waves go?
They go over the beach since they are much wider and carry a large volume of water.
Class Question #2
How are storm waves different from tsunamis?
a) Storm waves have deeper wave bases than tsunamis.
b) Storm waves have more dynamic pressure than tsunamis.
c) Storm waves have shorter drawbacks and wave periods than
tsunamis.
d) Storm waves contain greater volumes of water than tsunamis.
c) Storm waves have shorter drawbacks and wave periods than
tsunamis. (correct answer)
Destruction from Tsunamis, list the 3
Drawback: Debris and sediments are tumbled and crushed, sand is stripped from beach
Rising Water: Carries boats inland breaking chains, harbors fill up with water
Water moving on shore: Vehicles, trees, and debris are tumbled and crushed, buildings are crushed or carried off foundations
Convergent Boundaries
Normal faults develop in sinking lithospheric plates. Thrust faults develop in accretionary prisims
Sudden vertical movement displaces water, what do normal, thrust, and strike slip faults do?
Normal: Pull water below equilibrium level
Thrust: Lift water above equilibrium level
Strike Slip: Do not often produce vertical motion
Accretionary Prism (AP) at convergent margin does,
- Shortens horizontally
- Thickens vertically
- Land elevation slowly rises
What two motions occur to AP when slip occurs?
- Face quickly moves seaward
- Land elevation quickly sinks
What are the Ghost Forests of Cascadia?
Land that has been subsided and has risen again, is filled with dead cedar trunks
Continential Margin Sticks
Margin shortens horizontally and rises vertically. Forests grew on dry land.
Continental Margin Slips
Margin moves westward from megathrust earthquake
Land surface subsides and becomes a salt marsh
Forests die in salt water
Peat forms in salt marshes
How where the Ghost Forests formed?
By Margin stick, then Margin slip, then margin stick
Class Question #3
What are emergency officials doing to protect the populations of
coastal Washington and Oregon from a future megathrust earthquake?
a) creating maps illustrating near-field tsunami inundation levels
b) measuring slip along the San Andreas fault and creating models
predicting future movement
c) draining coastal areas that may be subject to sudden flooding as a
result of subsidence
d) excavating slopes and creating levees to direct and control sudden
flows of seawater
a) creating maps illustrating near-field tsunami inundation levels
(correct answer)
Subaerial Land slides
Push waters surface down
Submarine landslides
Pulls waters surface down, landslide toe pushes waters surface up
Class Question #4
Select the tertiary disaster that resulted from the 1998 Papua New
Guinea tsunami.
a) Two thousand people were killed by the tsunami that carried sand,
coral, and debris.
b) The force of the wave flattened palm trees on barrier islands
between the sea and lagoons.
c) Numerous villages along the northern coast were destroyed by the
tsunami.
d) Witnesses suffered post-traumatic stress and became distraught
when discussing the event, even years later.
d) Witnesses suffered post-traumatic stress and became
distraught when discussing the event, even years later. (correct
answer)
Secondary disasters from Tsunamis include,
Tsunamis destroy roads and
bridges.
Tsunamis cut power, water, gas,
and sewage lines.
Transportation and essential
emergency services are blocked.
Mold and rot are common.
Lack of sanitation creates
cholera and dysentery
infections.
Malaria cases rise from
increased mosquito breeding.
Poor, marginalized communities
are left traumatized and jobless.
Tsunami relive and recovery is challenging because,
Roads are buried or damaged. Communication systems are destroyed
Hover crafts may be the only way to access communities
Ships often become hospitals
Tsunami relief priorities
- Food
- Water
- Shelter
- Health care
DART Buoys are? and are used for?
They are buoys that send signals to satellites, from tsunami pressure pulses under the water which are read by a pressure recorder.
Class Question #5
How do DART buoys work?
a) Buoys emit loud sirens to warn coastal communities of an incoming
tsunami wave train.
b) Buoys send “take cover” emergency messages to social media apps.
c) Buoys send warnings that travel at the speed of light to a receiver on
land.
d) Buoys create an interlocking superstructure that slows tsunami
wave trains while they are in the open ocean.
c) Buoys send warnings that travel at the speed of light to a
receiver on land. (correct answer)
NOAA organizations include,
- Pacific Tsunami Warning Center
- National Tsunami Warning Center
- Calculate potential tsunami arrival times
Tsunami watch
conditions exist that may generate a tsunami
Tsunami warning
A tsunami is approaching
Public awareness
Communication and response plans are essential.
