WA L2: Destructive Ocean Waves Flashcards
1
Q
What is a storm surge?
A
Abrupt bulge of water driven ashore by a hurricane (or similar event elsewhere: tropical cyclone, typhoon).
2
Q
What two processes generate a storm surge?
A
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
3
Q
What is a wind-driven surge?
A
tall large water mound created by hurricane winds
4
Q
What is pressure surge?
A
The effect of air pressure that raises ocean water (suctions it) underneath the eye of the storm
5
Q
Is the surge technically a wave or a crest?
A
It is only a crest.
6
Q
Behaviour of surge?
A
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.
7
Q
What about storm surges differ from common oceanic waves?
A
Storm surges do not break into surf.
8
Q
When are storm surges most disastrous? Why?
A
During high tide. Because the height and mass of water of the tide adds onto that of the surge
9
Q
How long do storm surges usually last?
A
1-3 days
10
Q
How much will the coastal water level be raised?
A
Raised by 0.5 to 7 meters.
11
Q
What determines the severity of the storm surge?
A
Strength of the storm generating the surge
12
Q
Where in the Northern Hemisphere do you experience the severest force of the surge?
A
The coastal area to the right of the storm
13
Q
surge driven by the wind is moving in the same direction (towards the shore) as the surge driven by the ___ ______ of the storm.
A
low pressure
14
Q
On the left side of the storm, which type of surge moves towards the shore? Why?
A
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.
15
Q
Why is the force of the storm surge on land at a minimum?
A
There is only pressure driven surge moving towards the shore.
16
Q
What kind of death is most common from surges?
A
Drowning. Usually from being swept off by the moving water. Impact of moving water also causes much of the damage to the structures.
17
Q
Would you expect most hurricane-related deaths in North America be due to storm surge? Why/ why not?
A
No. Most of us live inland. Hurricanes destroy more infrastructure, I think…
18
Q
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?
A
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.
19
Q
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?
A
Bay of Bengal area. 142 events recorded. Some taller than 8m. The surges killed 100’s of thousands of people
20
Q
How to protect oneself from hurricanes?
A
Make sure you have emergency kit and plan and by evacuating when told.
21
Q
Where do hurricanes strike Canada?
A
the Atlantic Coast.
22
Q
Action plan to protect you and family from storm surges?
A
Step 1: Listen for warnings
Step 2: Be prepared
Step 3: Take appropriate action
Step 4: Know what your community is doing
23
Q
What to do should a storm surge occur?
A
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
24
Q
What is a tsunami? What does the word come from?
A
A wave or series of waves generated by the rapid displacement of large amounts of ocean water. Comes from Japanese term “harbour wave.”
25
Why is the term "tidal wave" incorrect nowadays for tsunami?
Tsunami are not related to tides at all.
26
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
27
What are seismic sea waves?
Tsunami generated by earthquakes
28
How can a mega-tsunami be generated?
Vertical thrust at subduction zones when the oceanic plate dives underneath the continental plate.
29
Most common cause of tsunami?
Submarine earthquakes
30
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.
31
What is a run-up?
Maximum vertical height above sea level that a tsunami reaches onshore.
32
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.
33
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.
34
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.
35
how can submarine landslides cause tsunami?
can generate tsunami when the moving mass creates a large displacement of the water column
36
How can submarine landslides be triggered?
may be triggered either by an earthquake or a volcanic eruption on land
37
Which events involve rapid addition of mass into the ocean?
Submarine landslides, icebergs falling from glaciers, meteor impacts
38
What kind of tsunami can impact events cause?
mega-tsunami
39
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
40
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
41
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%
42
Only _% of the tsunami have struck Alaska and the West Coasts of Canada and the U.S.
7
43
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.
44
What magnitude was the Cascadia earthquake that triggered the tsunami?
moment magnitude 9
45
The Cascadia tsunami event is similar in behaviour and size to which other tsunami?
the one generated in 1960 by an earthquake off Chile
46
Which places were affected by the Cascadia 1700 tsunami?
the coasts of British Columbia, Oregon, Washington, northern California, and Japan
47
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
48
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
49
What is an important source of information about previous tsunami?
geologic deposits
50
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.
51
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.
52
How was the Krakatau 1883 tsunami generated?
the colossal eruption and collapse of the volcanic island of Karaktau. Indonesia.
53
How tall is tsunami wave of Kratakau 1883?
up to 30m high
54
What happened to Kratakau during eruption?
Essentially exploded and disappeared from the face of the Earth.
55
Scope of the Kratakau tsunami?
Tsunami was only destructive locally in Indonesia.
56
When did the Meiji Tsunami occur?
In the summer of 1896
57
How many Japanese died in the Meiji Tsunami?
22 000 Japanese
58
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.
59
What was the most devastating tsunami in Japan's history?
Meiji tsunami
60
Where and when did the first wave of the Meiji Tsunami arrive?
at the Sanrika coast 35 mins after earthquake
61
Run-up of Meiji Tsunami?
25 meters
62
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.
63
What served as momentum for tsunami research in Japan?
the Meiji Tsunami
64
Describe the 1998 Papua New Guinea tsunami.
generated about 8 km offshore. Tsunami waves arrived on shore only a few minutes after the earthquake. There were 2,200 deaths.
65
Describe the 2004 Indian Ocean tsunami.
generated offshore along a 1,200 km fault line. The first waves arrived on shore about 15 minutes after the earthquake.
66
In modern Japan, what do they train children to do?
Run to higher ground as soon as an earthquake is felt.
67
Which tsunami highlights the fact that the severity of the generating earthquake does not ALWAYS determine the magnitude of the ensuing tsunami?
Meiji tsunami
68
Describe the Grand Banks, Newfoundland 1929 tsunami.
Date: Nov 18 1929
7.2 magnitude earthquake offshore of Newfoundland on the Grand Banks. Earthquake itself (from seismograph data) caused little motion, but it triggered huge submarine landslide on the continental slope. Landslide triggered tsunami. 2.5 hours later, massive waves struck coast of Newfoundland. 28 people died in towns on the Burin Peninsula. Waves were recorded elsewhere on the eastern seaboard of North America and across the Atlantic in Portugal
69
What is a turbidity current?
Rapid, downhill flow of water caused by increased density due to high amounts of sediment. Turbidity currents can be caused by earthquakes, collapsing slopes, and other geological disturbances
70
Grand Banks, Newfoundland tsunami: towns on the Burin Peninsula that were at the ____ of long, ____ bays were most damaged. Much human infrastructure was destroyed, as well as more than _____ pounds of already caught and salted cod.
heads; narrow; 280 000
71
What is one of the most important lessons learned from the Grand Banks earthquake, landslide, and tsunami?
behaviour of submarine landslides. Many trans-Atlantic communications cables are laid across this area of the sea floor, connecting North America and Europe. The mass movement of mud and sand broke a series of cables in succession down the slope. Based on the timing of cable breaks (communication disruptions) in known locations, people were first able to estimate the speed of submarine landslides at more than 90 kph! The tsunami itself, as a shallow water wave, would have traveled nearly 10 times this speed and therefore was not responsible for the cable breaks.
72
What does the 1929 Grand Banks event demonstrate?
The 1929 Grand Banks event demonstrates that:
a) devastating earthquake-related tsunami can occur in areas not associated with tectonic plate boundaries
b) tsunami usually occur in association with one or more other natural disasters (earthquake, landslide, etc.)
73
What is the most destructive Pacific-wide tsunami? Where was it most severe?
The 1946 tsunami event. Most severe in the State of Hawaii.
74
Describe the 1946 earthquake. Where/when it occur? Magnitude?
April 1 1946. Aleutian Islands, Alaska. Magnitude 7.2 on Richter scale, moment magnitude 8.6.
75
Run-up of 1946 tsunami in Alaska?
35 meters
76
How long did it take the 1946 tsunami to reach the coastal population of the Big Island of Hawaii?
4.5 hours
77
Why was there so much damage in Hawaii despite the waves taking hours to arrive?
No warning system in place. People were caught unaware.
78
The town of Hilo on the eastern side of the Big Island of Hawaii was pounded by a series of _ to _ large waves coming in at minute intervals. The highest of these waves had a run up height of __ metres above sea level.
6 to 7; 15-20; 8.1
79
Which waterfront did the 1946 tsunami completely destroy?
Hilo
80
Damage to property cost for town of Hilo after tsunami?
US $26 million dollars (in 1946 dollars)
81
Death toll for Hilo after tsunami?
150-170
82
Why were the effects of the tsunami magnified at Hilo Bay?
Hilo Bay is shaped like a funnel with the town of Hilo at the neck. This configuration focuses the onrushing water from the mouth of the Bay into Hilo (just like a funnel is meant to do).
83
Furthermore, because of the local geographic peculiarity of Hilo Bay, its natural resonant period of about ___ minutes was in phase with the 1946 tsunami that had a __-minute interval between wave fronts. This meant that every second wave was __ _____ with the motion of Hilo Bay, creating a ____ in the Bay. The ____ generated by the tsunami continued for several ___ after the devastation. The effects of the ____ and the incoming waves were additive and cause much greater destruction than just the ____ or the tsunami alone.
30; 15; in phase; seiche; seiche; days; seiche; seiche
84
What characteristics of tsunami waves did the 1946 Tsunami event that struck Hawaii highlight?
Summary
The 1946 Tsunami event that struck Hawaii highlighted several characteristics of tsunami waves:
a) tsunami travel long distances across the ocean without losing energy
b) much of the death and damage from a tsunami can be minimized if an appropriate warning system is in place
c) local topographic features magnify the effects of tsunami, making Bays and Harbours especially vulnerable to extensive damage from these ultra-large waves
85
What was established in Hawaii in 1948 after the 1946 "April Fool's Day" tsunami?
the Pacific Tsunami Warning Center. Later expanded and became headquarters of the International Pacific Warning System.
86
Run-up of Lituya Bay, Alaska, 1958?
516 m at the head of Lituya Bay, Alaska
87
What triggered the Lituya Bay tsunami?
combination of disturbances triggered by 8.3 magnitude earthquake on July 1958. strong earthquake triggered a giant rockfall at the headland of the bay, resembling an asteroid, impacted the bottom of Gilbert Inlet. Impact created a crater, displaced sedimentary layers and uplifted 400 m of ice along front of Lituya Glacier. Impact also resulted in water splashing that reached 516 m high.
88
What happened to the forest on Cenotaph Island? To the fishermen on boats at the mouth of the Bay ("La Chusse Spit")?
Forest on Cenotaph Island was stripped. Fishermen were either lost at sea or survived the ordeal. Seiche was also generated in the Bay by the tsunami.
89
A combination of forces can generate waves with record-breaking _____, especially when local topographic features allow the forces to be confined into a ____ space.
run-ups; small
90
What generated one of the most destructive tsunami to hit Hawaii and the rest of the Pacific in this century?
Mw 9.5 earthquake, one of the largest earthquakes ever recorded.
91
Where in the world was the Mw 9.5 earthquake and its tsunami most destructive?
Chile, especially in coastal area where tsunami run-up was as high as 25 m.
92
What is the draw down?
trough of the tsunami
93
What did the inhabitants in Chile do prior to the tsunami?
They feared the earthquake and took to small boats to escape the shaking.
94
When did the draw down arrive for the tsunami in Chile in 1960?
10 to 15 minutes after the quake. Along more than 500 m of the coast.
95
How far did the 1960 tsunami spread inland in Chile?
half a km inland
96
Total deaths along the Chilean coast in 1960 tsunami?
2 000 people
97
The 1960 pacific-wide tsunami caused particularly a lot of damage in which two places besides Chile? How many people died in these two locations? Damage cost?
Hawaii and Japan. 2000 deaths. Damage costs estimated at over half a billion U.S. dollars
98
How many hours and distance did the 1960 tsunami travel for before reaching Hilo?
15 hours, about 10 000 km
99
What allowed the Hawaiian coastal communities of Hilo to evacuate in time? How many deaths?
the Pacific Tsunami Warning Center. 61 deaths, mostly curious onlookers
100
How is tsunami forceful?
both as the water moves inland with the crest of the tsunami and as the water recedes back to the ocean with the trough of the wave.
101
Following this destructive tsunami and its international effect around the Pacific Ocean, the need for an ____ _____ _____ _____ was recognized. UNESCO and the U.S. government co-sponsored the establishment of the International Tsunami Warning System to be based in _____, Hawaii.
International Tsunami Warning System; Honolulu
102
From this tsunami experience, we learned that:
a) boats _____ or afloat close to shore are very vulnerable to tsunami effects
b) tsunami travel at tremendous speeds over long distances without _____ any of its energy
c) despite sophisticated warning systems in place, lives will be lost if _______.
d) the force of a tsunami is destructive during both its ____ and its ____ from land
anchored; dissipating; the warnings are not followed; advance, retreat
103
Vaiont Dam tsunami: the impact of the landslide displaced as much as __% of the water within the lake.
50
104
What caused the Vaiont Dam 1963 tsunami in Italy?
a landslide in a river caused a man-made tsunami (because there was the dam)
105
Run-up the Vaiont Dam 1963 tsunami? Where?
300 m above lake level, wiped out town of Casso, which was 260m above lake level. Tsunami traveled up and downstream simultaneously.
106
How many deaths in the Vaiont Dam 1963 tsunami?
2600 deaths
107
From the Vaiont Dam tsunami experience, we learned that:
a) although rare, tsunami can be generated in places far removed from the ocean, such as in the _____ ___
b) _______ activities can induce natural disasters
Italian Alps; anthropogenic
108
Largest earthquake ever recorded in North America?
1964 "Good Friday" earthquake that occurred in Prince William Sound, Alaska
109
Where did the 1964 Good Friday Earthquake's tsunami hit? Which place was most affected?
It hit parts of BC and several other cities on the west coast. Particularly destructive at Port Alberni in Vancouver Island
110
Why did tsunami take the same amount of time to travel between Prince Rupert and Tofino (at 1400kph) AND the shorter distance between Tofino and Port Alberni? (at 420 kph)? i.e. Why did the tsunami slow down so much?
The location of Port Alberni at the head of Alberni Inlet, a 40-km long and narrow channel accounts for the longer tsunami travel time. Tsunami are shallow water waves and thus slow down as they travel over shallower water.
111
A tsunami consists of a ____ of waves that have very long wavelengths, hence transport a large amount of energy. It is not possible to predict which wave, the first, middle or last wave is the tallest or the most destructive. Any one of the waves in the series can be the tallest or the more devastating one. At Port Alberni, the most destructive wave arrived as late as ___ hours after the earthquake.
series; 5.5
112
Why was the tsunami most destructive at Port Alberni and not any other coastal towns on Vancouver island?
The funnel shape and configuration of the inlet were the main reasons for the extensive flooding and damage that occurred in Port Alberni. The narrow inlet leading to Port Alberni focused the energy from the tsunami into a very narrow space, magnifying its effect. The most destructive wave arrived about an hour after the first wave. It came with such great force and energy, enough to travel up to a kilometre inland. The wall of water pushed everything in its way, causing much damage by carrying homes, buildings, and cars far inland.
113
The Port Alberni tsunami event demonstrates that:
a) the shape and _______ of coastal water bodies greatly affect the behaviour of tsunami as it approaches land
b) ___, narrow channels magnify the force of tsunami, causing more massive destruction and effects farther inland
configuration; long
114
Greatest earthquake ever recorded in 40 years?
On Dec 26 2004, 150 km off the west coast of Sumatra, Indonesia.
115
How many countries were affected in the 2004 worldwide tsunami? Where were they located?
11 countries bordering the Indian Ocean
116
Main cause of ~225 000deaths from the 2004 event?
tsunami. wiped out entire coastal areas across Southeast Asia, Sri Lanka, India, Thailand, Myanmar, island countries in the Andaman Sea, and the Maldives in the Indian Ocean.
117
Why so many deaths in 2004 event?
no tsunami warning system existed for the Indian Ocean as there was for the Pacific Ocean. People were surprised.
Also, ITWS (Int. Tsunami Warning System) said most likely tsunami was generated, but no tide gauges nor pressure sensors, so no way to confirm the tsunami. Also, no protocols in place for the ITWS to extend any warning to the countries concerned.
118
What was the task of the PTWC (Pacific Tsunami Warning Center)?
monitor and warn civil and military authorities in the Hawaiian Islands and elsewhere about impending tsunami
119
In 1953, the PTWC's coverage expanded to include which places?
the U.S. west coast States of California, Oregon, and Washington
120
Following the ______ tsunami that exacted a large number of deaths and massive destruction in three countries in the Pacific Ocean, the need for an international warning system was recognized.
1960 Chilean
121
UNESCO and the U.S. sponsored the establishment of the _______ (PTWS) based in the same headquarters as the PTWC in Hawaii.
Pacific Tsunami Warning and Mitigation System
122
The PTWS currently has __ member nations, mostly from the Pacific, and involves the use of __ seismic stations, __ tide stations, and ___ information dissemination points located in the Pacific Basin.
25; 24; 53; 100
123
How does the PTWS work?
1. An earthquake of sufficient size to trigger the alarms, set at the threshold of 6.5 on the Richter Scale, is detected.
2. Seismic data is collected, the earthquake is located, and its magnitude is computed.
3. Reports from tide stations are monitored for any indication that a tsunami has been generated, i.e., anomalous changes in wave height other than that from tides.
4. If so, a warning is transmitted to the participating agencies (information dissemination points) for relaying to their respective public constituents.
5. Predetermined plans to evacuate people from endangered areas are implemented.
124
In addition to the Pacific Tsunami Warning and Mitigation System, a number of ________ have been established to monitor and warn the population in areas where tsunami frequency is high and where immediate response is necessary. Where have such tsunami warning systems have been established?
Regional Warning Systems; Soviet Union, Japan, Alaska, and Hawaii
125
Which tsunami warning center is BC covered by?
West Coast and Alaska Tsunami Warning Cente
126
Where is the PTWC in Hawaii currently serving as the interim Warning Center for?
the Indian Ocean, South China Sea, Caribbean Sea, and Puerto Rico and U.S. Virgin Islands
127
What are tsunameters?
A seafloor bottom pressure recording (BPR) system capable of detecting tsunami as with a wave height as small as 1 cm (in the middle of the ocean). The data generated by the bottom meters are transmitted to the moored surface buoy which then sends the data to various Warning Centers via real-time communications.
128
What is DART?
"Deep-ocean Assessment and Reporting of Tsunamis." Fairly new monitoring system developed by the Pacific Marine Environmental Laboratory (PMEL). It is a real-time tsunami monitoring system consisting of "tsunameters" (monitoring devices) and buoys positioned at strategic locations throughout the world's ocean.
129
How many DART locations in the world currently?
39
130
How do tsunami differ from wind-driven oceanic waves?
Wavelength and period; tsunami are hundreds of km in wavelength vs. hundreds of meters for wind waves. Minutes to an hour in period for tsunami vs. seconds for common wind waves. Tsunami are giant waves compared to wind-generated ocean waves
131
Period of: short wind-blown wave? medium wind-blown wave? long wind-blown wave?
5s, 10, 20s
132
Length of: short wind-blown wave? medium wind-blown wave? long wind-blown wave?
40m, 155m, 625m
133
period of very long tsunami? length very long of tsunami?
3600s, 837 000m
134
```
Typical wave characteristics of tsunami:
Wavelength (L): ?
Wave speed (S): ?
Wave height (H): ?
Period (T): ?
```
200 km, 200 m/s or 720 km/h, 0.5 to 1 m, 10 min to 1 hour
135
Knowing typical tsunami characteristics, what do you think determines tsunami speed?
ocean depth
136
Describe how tsunami approach shore.
wave speed S or V decreases to ~60 kph
wave height H increases to several metres up to > 30 metres
wavelength L decreases as waves begin to "pile up" due to increased friction with the ocean floor
tsunami involve a series of peaks and troughs
the first wave may not be the biggest
the trough of a tsunami may arrive first in which case the sea level may be observed to recede first (called a draw down)
destruction from a tsunami comes with the advance AND retreat of all waves
destruction from a tsunami is not due to the high waves crashing down but due to the momentum (speed and mass) of the large mass of water and the ultra-long wavelength and period
tsunami wave height can be exacerbated by local bottom topography and shape of the shoreline
restricted bays and harbours magnify local effects
the mass of water brought by a tsunami can travel great distances inland
channels, rivers, and streams act as conduits for the delivery of energy within a confined space
137
What type of earthquake is a threat in BC?
megathrust
138
BC residents at high-risk areas must be aware that a strong near-shore earthquake may generate a ____ _____.
This means that the tsunami may arrive on shore within __ minutes of a subduction earthquake. Therefore, it is highly recommended that those in these areas (see map below) move ___ or to ___ ____ immediately as soon as they feel strong ground shaking. Emergency officials may not have time to issue a warning.
local tsunami; 10; inland or to high ground
139
Why is a place like Zeballos in BC especially vulnerable?
its location is at the end of a long ocean inlet (long and narrow!)
140
Tsunami safety rules?
A strong earthquake felt in a low-lying coastal area is a natural warning of possible, immediate danger.
Keep calm and quickly move to higher ground away from the coast.
When you hear that an earthquake has occurred in the ocean or coastline regions, prepare for a tsunami emergency.
Be aware that tsunami can occur at any time, day or night and that they can travel up rivers and streams that lead to the ocean.
A tsunami is not a single wave, but a series of waves. Stay out of danger until an "ALL CLEAR" is issued by a competent authority.
Approaching tsunami are sometimes heralded by noticeable rise or fall of coastal waters. This is nature's tsunami warning and should be heeded.
Approaching large tsunami are usually accompanied by a loud roar that sounds like a train or aircraft. If a tsunami arrives at night when you cannot see the ocean, this is also nature's tsunami warning and should be heeded.
A small tsunami at one beach can be a giant a few kilometres away. Do not let modest size of one make you lose respect for all.
Sooner or later, tsunami visit every coastline in the Pacific. All tsunami - like hurricanes - are potentially dangerous even though they may not damage every coastline they strike.
Never go down to the beach to watch for a tsunami!
WHEN YOU CAN SEE THE WAVE, YOU ARE TOO CLOSE TO ESCAPE.
Tsunami travel faster than a person can run!
During a tsunami emergency, your local emergency management office, police, fire, and other emergency organizations will try to save your life. Give them your fullest cooperation.
Homes and other buildings located in low-lying coastal areas are not safe. Do NOT stay in such buildings if there is a tsunami warning.
The upper floors of high, multi-story, reinforced concrete buildings/hotels can provide refuge (vertical evacuation) if there is no time to quickly move inland or to higher ground.
If you are on a boat or ship and there is time, move your vessel to deeper water (at least 2,000 metres). If there is concurrent severe weather, it may be safer to leave the boat at the pier and physically move to higher ground.
Stay tuned to your local radio, marine radio, Weather Radio, or television stations during a tsunami emergency. Bulletins issued through your local emergency management office and National Weather Service offices can save your life.
141
What aspect of a tsunami is the most predictable?
their wave speed.
142
What is a seiche?
a resonant wave in a body of water caused by a disturbance by wind or seismic activity. The water sloshes back and forth within the water body, with the wave racing between opposing shores.
143
Where do seiches commonly form?
in lakes or landlocked seas but can also form in semi-enclosed water bodies
144
On the Great Lakes, a seiche is often called a ___. It is always present, but is usually too small to be noticeable, except during periods of unusual calm.
slosh
145
Which lake prone to wind-caused seiches and why? How tall can they be on this lake?
Lake Erie. Because of its shallowness and elongation. Up to 5m.
146
Effect of a seiche is similar to what? What makes the seiche more dangerous?
A storm surge. Seiche can oscillate back and forth across body of water for some period of time.
147
In a few of the tsunami case studies discussed, seiches were observed to be generated when a tsunami entered a semi-enclosed body. ____ in Hawaii, has been identified as a location that is critically vulnerable to damaging effects from a tsunami. WHY?
Historically, the tsunami damage suffered by the residents of ___ has been a combination of the effects of the tsunami and the tsunami-generated seiche.
Hilo Bay; because the Bay has a resonance that is a factor of the tsunami period. ; Hilo
148
During the _______ earthquake, seiches were generated in swimming pools all over Southern California. Many of them overflowed. The __________ earthquake that devastated Port Alberni generated seiches in swimming pools in as far away as Puerto Rico!
1994 Northridge;
1964 "Good Friday"
149
Waves don't usually reflect (bounce back) when they strike other waves. Instead, they combine or are _______, either constructively or destructively.
superpositioned
150
When does constructive interference occur?
occurs when the wave amplitudes (half the vertical distance between a trough and a crest) reinforce each other, building a wave of even greater amplitude, i.e. bigger waves.
151
When does destructive interference occur?
occurs when the wave amplitudes oppose each other, resulting in waves of reduced amplitude, namely smaller waves. The figures below illustrate wave interference
152
What are rogue waves?
also known as monster waves, are large and spontaneous ocean waves which can sink even large ships and ocean liners. Rogue waves are caused by the constructive interference between two wave trains.
153
Why are rogue waves far larger than expected?
They result from constructive interference of 2 different wave trains. Their unexpected nature makes them very dangerous especially if over-steepened (H/L >= 1/7)
154
Severe weather has sunk more than ___ supertankers and container ships exceeding ___ metres in length during the last two decades. According to studies conducted by the __________ (Links to an external site.), ______ are believed to be the major cause in many such cases.
200; 200; European Space Agency; rogue waves
155
Rogue waves are notorious off the _________. In this location, waves generated in the Antarctic Ocean run into three strong currents (____ Current, _____ Current, and the _________ Current) creating an environment with a very high probability of rogue waves being produced from interference.
Cape of Good Hope, South Africa; Agulhas; Benguela; Antarctic Circumpolar
156
Rogue waves have also been observed to hit the coast. In 1992, a calm () beach was hit by a 5.5 m monster wave throwing 75 people off their feet causing injuries.
Florida
157
Why can't we take safety precautions against rogue waves?
They're unpredictable.
