Tsunami

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1

what are seismic sea wave?

  • an abnormally long wavelength wave produced by sudden displacement of water

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2

what is a near field tsunamis?

  • tsunami that strikes areas adjacent to its point of origin

  • there is little warning

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3

what is far field tsunami?

  • tsunami that strikes areas distant from its point of original

  • can impact multiple countries around

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4

what are masses that may cause tsunamis?

  • the seafloor shifting up or down

  • a submarine and/or subaerial landslide

  • a pyroclastic flow

  • an air blast form an explosive volcanic eruption

  • a meteorite impact

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5

are tsunamis large tsunamis?

  • not tsunamis

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6

what are tsunami wave train?

  • groups of waves

  • consistent w/ earthquakes

<ul><li><p>groups of waves</p></li><li><p>consistent w/ earthquakes</p></li></ul>
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7

what are the tsunami wave characteristics?

  • long wave lengths

  • velocity dependent of water depth

    • the wave is so big that there is frictional interaction w/ the ocean bottom

    • wave slows down in shallower water → more friction

  • wave increases its height as the water becomes shallower near the coast

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8

wave height depends on?

  • the distance between source and location

  • the amount of water pushed by a mass

  • the shape and velocity of the mass pushing the water

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9

what creates waves refraction interference?

islands

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10

are tsunami waves big or small while crossing open ocean?

  • small

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11

what creates towering waves as they approach shore?

shoaling

<p>shoaling</p>
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12

wave velocity across open oceans?

  • around 700 km/hr

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13

does wave velocity slow or speed up as they enter shallow water?

slow

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14

how are big waves caused?

  • water at rear of wave catches up to slower water, increasing height

    • front slows down, back catches up → cause big wave

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15

what can prevent water from flowing inland?

  • steep cliffs

  • water may flow many km into gently sloping coasts

<ul><li><p>steep cliffs</p></li><li><p>water may flow many km into gently sloping coasts</p></li></ul>
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16

what occurs in a mega-thrust earthquake?

  • Megathrust earthquakes have \n an M W > 8.6.

    • at subduction zone

  • Accretionary prism (AP) at \n convergent margin.

    • Shortens horizontally

    • Thickens vertically

    • Land elevation slowly \n rises.

  • Two motions occur to AP \n when slip occurs:

    • Face quickly moves \n seaward.

    • Land elevation quickly \n sinks.

<ul><li><p>Megathrust earthquakes have \n an M W &gt; 8.6.</p><ul><li><p>at subduction zone</p></li></ul></li><li><p>Accretionary prism (AP) at \n convergent margin.</p><ul><li><p>Shortens horizontally</p></li><li><p>Thickens vertically</p></li><li><p>Land elevation slowly \n rises.</p></li></ul></li><li><p>Two motions occur to AP \n when slip occurs:</p><ul><li><p>Face quickly moves \n seaward.</p></li><li><p>Land elevation quickly \n sinks.</p></li></ul></li></ul>
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17

sumatra tsunami - Dec 26, 2004

  • 9.1 magnitude subduction zone earthquake

    • indian plate and burma plate

  • paleoseismic studies show that giant seismic events occur every 230 yrs

  • tsunami waves generated by this event rose 10 metres or more above sea lvl

  • 230,000 deaths

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18

Chile Tsunami - may 26, 1960

  • caused by 9.5 magnitude earthquake in subduction zone along the coast of Chile

  • 2000 people killed in Chile: 5700 people killed around the Pacific

    • Hilo, Hawaii, 61 deaths

    • Japan, 185 deaths

  • left a sand layer over the soil in a farmer’s field

  • alarm sys was placed after this

<ul><li><p>caused by 9.5 magnitude earthquake in subduction zone along the coast of Chile</p></li><li><p>2000 people killed in Chile: 5700 people killed around the Pacific</p><ul><li><p>Hilo, Hawaii, 61 deaths</p></li><li><p>Japan, 185 deaths</p></li></ul></li><li><p>left a sand layer over the soil in a farmer’s field</p></li><li><p>alarm sys was placed after this</p></li></ul>
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19

how can volcanoes generate tsunamis?

  • caldera collapse

  • submarine eruption

  • debris cloud collapse may trigger tsunamis

  • debris displaces sea surface when it falls

  • flank collapse

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20

do volcanos generate big tsunamis?

  • only small vol of water it moved

  • generate (relatively) small tsunamis

  • only impact local area

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21

Krakatau Eruption - 1883

  • in Sunda Strait

  • tsunami killed 36,000 on Sumatra and Java

  • pyroclastic flow may have displaced sea surface

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22

how frequent and severe are flank collapse?

  • <1% of tsunamis are caused by volcano flank collapse

  • can produce large near-field tsunamis

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23

what is example of flank collapse generated tsunami?

  • Anak Krakatau 2018

    • 400 deaths

    • 7,000 injured

    • 47,000 displaced from homes

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24

what percentage of tsunamis are caused by fast-moving landslides or rock avalanches?

  • around 1%

  • These types of tsunamis are created by fast-moving landslides (sediment) or fast-moving rock avalanches (broken bedrock) falling into the ocean and displacing a large volume of water. \n • Size of tsunami waves based on the mass of the materia

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25

example of rock avalanche generated tsunami?

  • Lituya Bay Alaska - July 9, 1958

  • released a 7.3 magnitude earthquake

  • wave was 150 meters high and surged metres above sea lvl

<ul><li><p>Lituya Bay Alaska - July 9, 1958</p></li><li><p>released a 7.3 magnitude earthquake</p></li><li><p>wave was 150 meters high and surged metres above sea lvl</p></li></ul>
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26

what % of tsunami are from submarine landslide?

  • around 5%

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27

do submarine landslide generate big tsunamis?

  • typically not as large as ones generated by landslide/rock avalanches from above sea lvl bc of the gentle slopes of the ocean floor

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28

example of submarine landslide?

  • Storegga slide

    • tsunami laid sediment (TLS) found above sea lvl on the Shetland Islands, Norway and Scotland

    • TLS consist of mud fragments ripped from the sea floor a\layers of well-sorted sand

    • we knew it happened cuz found an area of sand missing

  • Papua New Guinea landslide

    • an Mw 7.0 earthquake off northern coast of Papua New Guinea

    • 15-m-high wave front devasted northern coastline; 2,000 people died, 1,000 injured, 10,000 displaced

    • tsunami generated

    • region is remote, isolated and lacks modern medical facilities

    • infection and post traumatic stress created long impact

<ul><li><p>Storegga slide</p><ul><li><p>tsunami laid sediment (TLS) found above sea lvl on the Shetland Islands, Norway and Scotland</p></li><li><p>TLS consist of mud fragments ripped from the sea floor a\layers of well-sorted sand</p></li><li><p>we knew it happened cuz found an area of sand missing</p></li></ul></li><li><p>Papua New Guinea landslide</p><ul><li><p>an Mw 7.0 earthquake off northern coast of Papua New Guinea</p></li><li><p>15-m-high wave front devasted northern coastline; 2,000 people died, 1,000 injured, 10,000 displaced</p></li><li><p>tsunami generated</p></li><li><p>region is remote, isolated and lacks modern medical facilities</p></li><li><p>infection and post traumatic stress created long impact</p></li></ul></li></ul>
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29

example of tsunamis from meteorite impact?

  • 66 Ma, a 14-km-diameter asteroid struck the Yucatan Peninsula.

  • Impact created the 150-km-diameter Chicxulub crater.

  • Impact ended the Mesozoic Era and the Age of Dinosaurs.

  • Mega-tsunamis were generated from the impact and falling debris.

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30

what can we do in trough arrives on shore first?

  • we can tell that all the water runs away from shore providing some warming

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31

how can offshore coral reef play role in tsunami?

  • if coastal area surrounded by it, can provide some protection by forcing wave to break on reef

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32

how does lack of warming impact region?

  • difficult to disseminate info between and within countries

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33

what is the time between waves?

  • typic more than 30 mins

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34

which waves are the worse?

  • second or third waves often worse than first

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35

rising water hazards

  • boats carried inland as anchor and chains are lost

  • larbors fill like bathtubs

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36

water moving onshore issue

  • vehicles, trees, and debris and tumbled and crushed

  • buildings are crushed or carried off foundations

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37

drawback from tsunamis?

  • debris and sediment are tumbled and crushed

  • sand stripped from beach

  • human and animal fatalities occur at all stages

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38

tsunami aftermaths?

  • tsunamis destroy power lines, roads, bridges, water and gas line; fires starters

  • essential services cant reach victims

  • debris rots and molds

  • crops destroyed, salt deposition in soils

  • contamination of water supplies

  • disease due to water rotting things

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39

relief and recovery?

  • tsunami relief and recovery are challenging:

    • roads are buried or damaged

    • communication sys destroyed

  • hovercraft may be the only to way to access communities

  • ships often become floating hospitals

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40

near-field tsunami warming system?

  • arrival of tsunami less than 30 mins after tsunami trigger

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41

what are some far-field tsunami warming system?

  • travel time of tsunamis in the Pacific Ocean can be accurately calc based on topography of the ocean floor

  • tidal sensors and ocean-bottom sensors can detect waves as they move across the ocean

  • downside: cannot forecast the actual height of a tsunami wave

<ul><li><p>travel time of tsunamis in the Pacific Ocean can be accurately calc based on topography of the ocean floor</p></li><li><p>tidal sensors and ocean-bottom sensors can detect waves as they move across the ocean</p></li><li><p>downside: cannot forecast the actual height of a tsunami wave</p></li></ul>
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42

some adaptations to tsunami hazards?

  • land-use zoning

  • engineering structs to resist erosion

  • orient streets and buildings at right angle to the waves

  • well-rooted vegetation

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43

tsunami hazards adaptations in Japans?

  • seawall with stairway evacuation route used to protect a coastal town in Japan

  • water gate used to protect Okushiri Island → they automatically close within secs after earthquake shaking triggers seismic sensor

  • tsunamis stones in Japan warm not to build below certain elevations

  • tsunami inundation map increase public awareness

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44

tsunami from Cascadia Subduction-Zone earthquakes

  • cascadia subduction zone located 1,900 km offshore southern british columbia

  • sequences of tsunami-laid sediment (TLS) indicate historic tsunami impacts along the Pacific Northwest coastline

  • Mud → contains the remains of marine plants

  • tsunami → laid sand

  • peat at the base → consists of partially decayed saltwater marsh plants

<ul><li><p>cascadia subduction zone located 1,900 km offshore southern british columbia</p></li><li><p>sequences of tsunami-laid sediment (TLS) indicate historic tsunami impacts along the Pacific Northwest coastline</p></li><li><p>Mud → contains the remains of marine plants</p></li><li><p>tsunami → laid sand</p></li><li><p>peat at the base → consists of partially decayed saltwater marsh plants</p></li></ul>
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45

huge tsunami-flattened forest are now below sea level why?

  • bc of displacement during an earthquake of the coastal bulge offshore

<ul><li><p>bc of displacement during an earthquake of the coastal bulge offshore</p></li></ul>
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46

example of forest that got flattened?

  • ancient Sitka spruce forest in the bay at Neskowin, Oregon, was felled by a giant tsunami following a large subduction-zone earthquake of 1700

<ul><li><p>ancient Sitka spruce forest in the bay at Neskowin, Oregon, was felled by a giant tsunami following a large subduction-zone earthquake of 1700</p></li></ul>
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47

Japan earthquake

  • March 11 2011

  • Magnitude 9.0 earthquake

  • subduction zone earthquake

  • generated a tsunamis that swept across the pacific ocean

<ul><li><p>March 11 2011</p></li><li><p>Magnitude 9.0 earthquake</p></li><li><p>subduction zone earthquake</p></li><li><p>generated a tsunamis that swept across the pacific ocean</p></li></ul>
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