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81 Cards in this Set
- Front
- Back
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Triggers for tsunami |
- earthquakes that uplift the sea floor - landslides - volcano flank collapse - submarine volcanic eruptions - meteroites |
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how earthquakes cause tsunamis |
- displacing the seafloor - triggering a landslide that enters water |
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minimum earthquake level to trigger a tsunami |
M 7.5 |
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Stage 1 of tsunami |
displacement of the seafloor sets waves in motion that transmit energy outward and upward. When the waves reach the surface of the water they spread out |
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stage 2 of tsunami |
waves move rapidly, up to 500 km/hour, wavelength can be > 100 km, amplitude is often small, <1m |
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stage 3 tsunami |
as the tsunami approaches land, the water depth decreases the water then 'piles up' and causes: - decrease in speed - decrease in spacing of the waves - larger amplitude |
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stage 4 tsunami |
reaches land, can reach heights of dozens of meters, speed can be up to 50 km/h |
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tsunami event |
consists of a series of large waves reaching shore that can last for several hours |
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run up |
the maximum horizontal and vertical distances that the largest wave of a tsunami reaches as it travels inland. Essentially the geographic area impacts. |
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distant tsunami |
tele-tsunami, can go thousands of km from the source |
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local tsunami |
up to 100 km from its source, provides little warning |
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which regions are at risk |
subduction zones or across ocean basins from subduction zones - pacific ocean and Mediterranean Sea most at risk |
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primary effects |
flooding and erosion destroy beaches, coastal vegetation and infrastructure |
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secondary effects |
fires, contaminated water |
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natural service functions |
carry fertile sediment onto the land that can be used for agriculture |
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What happened with the Indian Ocean tsunami? |
subduction zone between Burma and Indian-Australian plates - M 9.1 earthquake - plates were locked & built up strain for 150 years - no warning system, > 230 000 deaths |
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early warning sign of tsunami |
the receding sea |
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Aftermath of the 2004 tsunami |
- new warning system in the Indian Ocean - needed an organized plan for evacuation - needed earthquake and tsunami education for people living along/visit the coastline |
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tsunameters |
sensors that rest on the seafloor and measure changes in water pressure passing over them. Sensors electronically connected to buoys. |
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means of structural control |
regulations on buildings & structures - Hawaii- some cities require flood proofing - concrete levees - offshore barriers |
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inundation maps |
show the run-up of previous tsunamis, helps to plan for future events - historical records, geologic data, and aerial photography help in making the maps |
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role of vegetation in tsunami |
can protect areas farther inland |
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passive margins |
distant from plate boundaries - wide continental shelves, sandy or pebble beaches, and barrier islands - ie North America, Canadian Arctic |
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active margins |
relatively close to plate boundaries - more rocky shorelines and sea cliffs - ie British Columbia coast |
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size of a wave depends on |
- velocity of the wind - duration of the wind - fetch - the distance wind blows across the water |
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swells |
sets of waves generated by storms far out at sea |
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cause of variation in wave height |
topography |
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how are breaking waves caused |
steep slope |
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plunging breakers |
form on steep beaches and can be very erosive |
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spilling breakers |
develop on wide, gently sloping beaches and are less erosive |
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tidal bores |
waves that form when inflowing tidal water in slowed by outflowing river water |
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beaches |
consist of loose material that has accumulated by wave action at the shoreline - material differs in colour and composition depending on its source area |
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surf zone |
area where waves move toward the shore after they break |
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breaker zone |
area where incoming waves peak and break |
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longshore bar |
low ridge on the seafloor in the breaker zone (sand bar) |
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longshore trough |
a depression on the seafloor formed by wave action landward of the longshore bar |
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littoral transport |
sand movement parallel to the shore |
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processes of littoral transport |
beach drift: sand moving in a zig-zag pattern in the swash zone longshore drift: transport sediment by currents that flow parallel to the shoreline |
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spits |
ridges that extend parallel to the shore from a point of land on a coast |
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barrier islands |
low, narrow islands separated from the mainland by a bay or lagoon |
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cause for daily fluctuations in sea level |
tides |
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eustasy |
global changes in sea level from melting ice sheets |
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isotasy |
forces that elevate or depress Earth's crust are called isostasy - can lead to local or regional changes in sea level - ie large ice sheet melts off of a continent, the reduction in weight causes the crust to slowly rise |
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rip currents |
horizontal currents that move away from the shoreline - sometimes called undertow |
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development of rip currents |
wives pile up water between the longshore bar and then water rushes back through the break - causes approx 100 deaths/year |
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sea cliff/bluff |
erosional landform that marks the landward boundary of a beach cliff cliff- salt water bluff- fresh water |
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berm |
an onshore portion of the beach that is generally flat and formed by a deposition of sediment |
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beach face |
onshore portion of the beach that slopes seaward. It lies within the swash zone (where waves repeatedly rush up and then back) |
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swash zone |
where waves repeatedly rush up and then back |
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cause of sea cliff and bluff erosion |
wave action, running water, and landslides |
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when does most erosion occur? |
during storms that bring powerful wind |
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highest erosion rates |
10 m annually |
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NA cities at the greatest risk from sea rise |
Vancouver, Miami, New Orleans, and New York |
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Maldives |
island nation of 300 000 people in the Indian Ocean, about 80% of the country is less than 1m above sea level - seawalls have been built around many of its islands to protect from waves up to 2 m in height |
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What is occurring with the climate change? |
more intense tropical storms and higher sea levels |
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natural service functions |
- scenic bluffs and coastal landscapes are a direct result of erosion - beaches are maintained by a constant deposition of sediment - coastal areas are popular tourist attractions for recreation |
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bluff |
a steep bank along a lake shore |
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tsunameter |
detects possible tsunamis |
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jetti |
constructed at the mouth of a river |
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run up |
the distance a tsunami surges inland |
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rip current |
flow of water out away from shore |
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tele-tsunami |
another name for distant tsunami |
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swash zone |
where waves run up and recede |
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barrier island |
long narrow ridge of land |
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inundation map |
displays run up map of previous tsunamis |
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Why are tsunamis rare in the Atlantic ocean? |
because the plates are diverging |
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Human interaction with coastal processes |
- Atlantic NA characterized by barrier islands, popular spot for resorts and condos - removal of sand dunes increases vulnerability to hurricanes |
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minimizing damage |
hard stabilization, soft stabilization, land-use |
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hard stabilization |
structures designed to protect the shoreline |
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soft stabilizaton |
addition of sand to depleted beaches |
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land-use |
avoid building in hazardous areas |
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seawalls |
structures built parallel to the shoreline - reflects waves and redirects energy to the shore - they tend to enhance beach erosion seaward of their base |
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groins |
built perpendicular to the shoreline usually in groups - trap sand from the longshore drift - accumulation of sand contributes to a wider beach but erosion still occurs in the downdrift area |
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breakwaters |
built parallel to shores and designed to protect boats in harbour or marina |
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jetties |
extend perpendicular to shoes at the mouth of a river. They are commonly built in pairs |
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objective of a jetty |
prevent sediment from accumulating at a river mouth and to shelter the river channel from large waves |
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beach nourishment |
adding sand to replace sand that has been eroded |
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E line |
the expected position of the shoreline after a specified number of years |
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E zone |
the area between the present shoreline and the respective E line |
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perception of coastal hazards |
based on past experience, proximity to the coastline, likelihood of property damage **the three P's- property damage likelihood, past experience, proximity |
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coastal zone management |
most structures should be considered temporary because of the dynamic nature of coastlines. Against the attitude of developers who believe that coasts are too valuable not to develop |
