WA L2: Destructive Ocean Waves Flashcards
What is a storm surge?
Abrupt bulge of water driven ashore by a hurricane (or similar event elsewhere: tropical cyclone, typhoon).
What two processes generate a storm surge?
a) hurricane winds pushing water into a large/tall mound called the wind-driven surge
b) raising of ocean water (due to air pressure), suctioned upward underneath the eye of storm because of low air pressure at the ocean surface. this second process produces a smaller effect
What is a wind-driven surge?
tall large water mound created by hurricane winds
What is pressure surge?
The effect of air pressure that raises ocean water (suctions it) underneath the eye of the storm
Is the surge technically a wave or a crest?
It is only a crest.
Behaviour of surge?
Behaves like shallow-water wave in that the bulge becomes higher as the water depth gets shallower. Bulge rushes inland as a sudden, very higher, wind-blown tide.
What about storm surges differ from common oceanic waves?
Storm surges do not break into surf.
When are storm surges most disastrous? Why?
During high tide. Because the height and mass of water of the tide adds onto that of the surge
How long do storm surges usually last?
1-3 days
How much will the coastal water level be raised?
Raised by 0.5 to 7 meters.
What determines the severity of the storm surge?
Strength of the storm generating the surge
Where in the Northern Hemisphere do you experience the severest force of the surge?
The coastal area to the right of the storm
surge driven by the wind is moving in the same direction (towards the shore) as the surge driven by the ___ ______ of the storm.
low pressure
On the left side of the storm, which type of surge moves towards the shore? Why?
Pressure-driven surge. On the left side of the storm, the winds are directed away from land (offshore); it is opposite to the direction of the storm.
Why is the force of the storm surge on land at a minimum?
There is only pressure driven surge moving towards the shore.
What kind of death is most common from surges?
Drowning. Usually from being swept off by the moving water. Impact of moving water also causes much of the damage to the structures.
Would you expect most hurricane-related deaths in North America be due to storm surge? Why/ why not?
No. Most of us live inland. Hurricanes destroy more infrastructure, I think…
In storm surge disasters, what does the significant decrease in the number of deaths and the exponential increase of cost of damage and destruction mean?
This data reflects our increased ability to forecast and predict the paths of incoming hurricanes and to use this knowledge to protect people who live along the coast. Unfortunately, governments have been unable to prevent society from developing large communities along the coast, especially in those low-lying areas that are highly vulnerable to the effects of storm surges.
What is the “storm surge capital of the world”? How many moderate to severe storm surges recorded from 1582 to 1991? How tall were some of them?
Bay of Bengal area. 142 events recorded. Some taller than 8m. The surges killed 100’s of thousands of people
How to protect oneself from hurricanes?
Make sure you have emergency kit and plan and by evacuating when told.
Where do hurricanes strike Canada?
the Atlantic Coast.
Action plan to protect you and family from storm surges?
Step 1: Listen for warnings
Step 2: Be prepared
Step 3: Take appropriate action
Step 4: Know what your community is doing
What to do should a storm surge occur?
stay inside where you are protected from the water; it’s best to be on the downwind side of the house, away from windows
if you are not all in the same location, keep in touch frequently with family members
monitor the storm’s progress and listen for warnings or instructions from local officials
flood waters can be dangerous to drive through; before driving anywhere, listen carefully to rescue officials who will be coordinating evacuation plans
be aware of risks such as hypothermia from cold water or drowning from running water
What is a tsunami? What does the word come from?
A wave or series of waves generated by the rapid displacement of large amounts of ocean water. Comes from Japanese term “harbour wave.”
Why is the term “tidal wave” incorrect nowadays for tsunami?
Tsunami are not related to tides at all.
Tsunami causes?
Earthquakes that cause a vertical submarine fault motion
Volcanic eruptions undersea or very close to shore
Landslides into the ocean
Icebergs falling from glaciers
Meteor impacts
What are seismic sea waves?
Tsunami generated by earthquakes
How can a mega-tsunami be generated?
Vertical thrust at subduction zones when the oceanic plate dives underneath the continental plate.
Most common cause of tsunami?
Submarine earthquakes
Do all undersea earthquakes result in a tsunami?
No. For example, the earthquake that devastated San Francisco in 1906 also produced 6-metre ocean floor fault displacements but did not generate any noticeable tsunami.
What is a run-up?
Maximum vertical height above sea level that a tsunami reaches onshore.
How is a tsunami generated by a submarine earthquake?
The vertical motion of the fault block pushes the water column above it upwards (or drops the water column downwards), transmits the seismic energy to the water column. The vertical movement of the water column is what starts the tsunami. These fault motions are commonly associated with subduction zones.
What is the “correct” kind of earthquake for generating a tsunami?
When a tectonic plate moves over or under another. Occurs at normal or reverse faults. Results in the seafloor moving vertically upwards or downwards. Earthquakes generated by two plates sliding past each other, such as in a strike-slip fault, do not result in any vertical motion of the seafloor, hence are unlikely to generate a tsunami.
How can a submarine volcanic eruption generate a tsunami?
During an undersea eruption, water is displaced when the seafloor abruptly deforms and vertically displaces the water column. Tsunami created as flanks of the volcano inflates or deflates and/or when gas and lava are ejected.
how can submarine landslides cause tsunami?
can generate tsunami when the moving mass creates a large displacement of the water column
How can submarine landslides be triggered?
may be triggered either by an earthquake or a volcanic eruption on land
Which events involve rapid addition of mass into the ocean?
Submarine landslides, icebergs falling from glaciers, meteor impacts
What kind of tsunami can impact events cause?
mega-tsunami
Also note from the list on Wikipedia that there have been more tsunami generated in the _____ _____ than in all of the other oceans combined.
Between 1900 to 2001, close to ___ tsunami were observed or recorded in the Pacific Ocean. Of these, 117 caused significant casualties and damage. In the 1990’s, __ significant tsunami events occurred in the Pacific Ocean alone
Pacific Ocean
800; 10
Exception in 1990’s to trend of increased ability to predict arrival of these destructive waves and ability to evacuate people to higher ground?
the thousands of deaths from the Flores Island, Indonesia tsunami in 1992 and the Papua New Guinea tsunami in 1998
Which country has suffered the most deaths from tsunami through history? What % of tsunami in the Pacific Ocean were generated in or near the islands of Japan?
Japan. 17%
Only _% of the tsunami have struck Alaska and the West Coasts of Canada and the U.S.
7
Describe the historic Cascadia event.
In 1700 a Cascadia subduction zone earthquake w/ an estimated magnitude 9 generated tsunami that hit the coasts of BC, Oregon, Washington, northern Cali, and Japan. Written records from Japan indicate that this tsunami was similar in behaviour and size to the one generated in 1960 by an earthquake off Chile. Oral histories of this tsunami describe the event in North America, but the disaster is far enough in the past that Canadian and American coastal communities don’t typically take tsunami danger as seriously as Japanese communities. A locally-generated tsunami like this one would have hit the North American coast less than an hour after an earthquake, leaving little time to prepare and evacuate.
What magnitude was the Cascadia earthquake that triggered the tsunami?
moment magnitude 9
The Cascadia tsunami event is similar in behaviour and size to which other tsunami?
the one generated in 1960 by an earthquake off Chile
Which places were affected by the Cascadia 1700 tsunami?
the coasts of British Columbia, Oregon, Washington, northern California, and Japan
Length of rupture of Cascadia 1700? Which is it similar to?
100s of km. Similar to length of rupture that caused 26 Dec 2004 tsunami in Indian Ocean
What human recorded information allows people to estimate the magnitude and source of the tsunami when no written records of the generating earthquake exist?
records of tsunami heights
What is an important source of information about previous tsunami?
geologic deposits
Describe the geologic deposits left behind by the 1700 tsunami.
left behind layers of sand several centimetres thick, oceanic material that was swept ashore with the incoming waves. These were deposited on top of low-lying coastal marshes and over human settlements, as evidenced by sand layers directly over fire pits along the Oregon and Washington coasts. Subsequently, coastal marsh environments were re-established on top of the tsunami deposits. Careful dating of these geological materials along the North American coast coupled with written histories from Japan help people piece together the extent of this disaster.
What does the 1700 Cascadia and tsunami demonstrate?
The 1700 Cascadia earthquake and tsunami demonstrate that:
a) Although the west coast of North America has not experienced a devastating tsunami in more than 300 years, the area is at risk for subduction zone earthquake generated tsunami.
b) Coastal geologic records can reveal important information about the extent, size, and timing of disasters that occurred prior to written record keeping.
How was the Krakatau 1883 tsunami generated?
the colossal eruption and collapse of the volcanic island of Karaktau. Indonesia.
How tall is tsunami wave of Kratakau 1883?
up to 30m high
What happened to Kratakau during eruption?
Essentially exploded and disappeared from the face of the Earth.
Scope of the Kratakau tsunami?
Tsunami was only destructive locally in Indonesia.
When did the Meiji Tsunami occur?
In the summer of 1896
How many Japanese died in the Meiji Tsunami?
22 000 Japanese
What caused the Meiji Tsunami? What is unusual about this event?
earthquake off the coast of Japan, very close to the Japan trench. Unusual: the size of the tsunami was much larger than would be expected from a 7.2 Richter scale size earthquake.
What was the most devastating tsunami in Japan’s history?
Meiji tsunami
Where and when did the first wave of the Meiji Tsunami arrive?
at the Sanrika coast 35 mins after earthquake
Run-up of Meiji Tsunami?
25 meters
What is the most dangerous kind of tsunami? Why?
Locally generated tsunami. Coastal communities do not have enough time to evacuate to higher ground before the first waves arrive.
