Waves 3 Flashcards
What is a tsunami?
rapid displacement of large amounts of ocean water when hit with massive jolt of energy
- ex/ sudden vertical change in a seafloor fault
Tsunami can be caused by what events?
- Earthquakes
- MOST often
- vertical displacement of sea floor - Volcanic eruptions
- Landslides
- Meteor impacts
- potentially the BIGGEST - Icebergs from glaciers
-> usually SMALLEST
What does the energy released by a seismic vertical motion do?
- flows away radially from point source
- propagates as wave train
- disturbs ENTIRE water column
What type of waves are tsunamis?
shallow water waves
ALWAYS
tsunami in the open ocean have large ___ and small ___
Large wavelengths (200-400km) and periods (1hr)
Small wave height (< 1m) and steepness («_space;1)
The period of a tsunami in open ocean is about
~ 10min to 1 hr
The wave speed of a tsunami in open ocean is
very fast, determined by depth
(average ocean depth is ~4500m)
(average speed 210m/s or 750km/hr)
What is the average ocean depth?
~4500m
True or False: All tsunami waves cross a given part of the ocean at the same speed
True
- speed depends on water depth
do tsunami waves break?
Not really
- def not in open ocean
- at coast, break at about 1m depth
- typically approach shore as an onrushing flood/surge for minutes
Can we outrun a tsunami?
no :(
As a tsunami reaches the shore, wave height could increase up to
30m
depending on shape of harbour
What’s the tsunami capital of US
Hilo, Hawaii
Why are tsunamis devastating in some semi-enclosed bays? What was an example of this?
due to resonance
ex/ Hilo Bay
Worsened because the tsunami wave period was a multiple of the basin’s natural resonant period…
What was the deadliest Tsunami in human history? (When, cause, deaths)
Indian Ocean Tsunami
Dec 2004
cause: M9 Subduction Zone Earthquake
deaths: > 200,000
Where do most tsunamis occur?
Ring of Fire in the Pacific Ocean
(Japan, Alaska, Chile, Indonesia, etc)
What kind of submarine earthquakes is needed to generate tsunamis?
Ones that create vertical motion
ex/ reverse faults, plates moving over one another, ruptured sea floor
Will a tsunami be created by slip earthquakes?
unlikely, two plates sliding past each other does not create vertical motion
How can volcanoes cause tsunamis?
land: dump mass into ocean
water: displace water when ejecting gas/lava
the ideal location for tsunami generation are ___ zones
subduction
Will we experience the crest or trough first?
Depends where you are relative to where tsunami is generated
Most recent Cascadia mega thrust quake
January 1700
What subduction zone is closest to us?
Cascadia
When a receding of water is observed, how long do we have before the tsunami (from Cascadian subduction zone) hits?
15-30 mins
How can we predict arrival time?
predict from celerity
= distance / ( 3.1 √depth )
How many tsunami warning centres do we currently have?
2
(PTWC) Pacific Ocean and Alaska (WC/ATWC)
Tsunami watch vs Tsunami warning
watch
- not confirmed, “might occur”
warning
- detected by buoys & tidal gauges, “have occurred”
What is the DART Buoy system?
Deep Ocean Assessment and Reporting of Tsunami
- measures pressure changes on seafloor caused by tsunami
- verify existence and tells warning centers
Describe how the DART Buoy system works
Tsunameter
- pressure sensor on ocean floor
-> can feel passing tsunami at bottom cuz they’re shallow waves!
Surface Buoy
- relays signal to PTWC via satellite
How many DART Buoys are there in world oceans
50
How to survive a tsunami
- natural warnings: receding water, strong earthquake
- listen to official warnings
- move boats into open ocean
- head to high ground
- animal behaviour
True or False: in the case of a tsunami warning, we should move boats even further into the ocean
true
open ocean is safe !
