Tsunami

what are seismic sea wave?

what are seismic sea wave?

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

what is a near field tsunamis?

• tsunami that strikes areas adjacent to its point of origin

• there is little warning

what is far field tsunami?

• tsunami that strikes areas distant from its point of original

• can impact multiple countries around

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

are tsunamis large tsunamis?

• not tsunamis

what are tsunami wave train?

• groups of waves

• consistent w/ earthquakes

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

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

what creates waves refraction interference?

islands

are tsunami waves big or small while crossing open ocean?

• small

what creates towering waves as they approach shore?

shoaling

wave velocity across open oceans?

• around 700 km/hr

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

slow

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

what can prevent water from flowing inland?

• steep cliffs

• water may flow many km into gently sloping coasts

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.

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

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

how can volcanoes generate tsunamis?

• caldera collapse

• submarine eruption

• debris cloud collapse may trigger tsunamis

• debris displaces sea surface when it falls

• flank collapse

do volcanos generate big tsunamis?

• only small vol of water it moved

• generate (relatively) small tsunamis

• only impact local area

Krakatau Eruption - 1883

• in Sunda Strait

• tsunami killed 36,000 on Sumatra and Java

• pyroclastic flow may have displaced sea surface

how frequent and severe are flank collapse?

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

• can produce large near-field tsunamis

what is example of flank collapse generated tsunami?

• Anak Krakatau 2018

  • 400 deaths

  • 7,000 injured

  • 47,000 displaced from homes

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

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

what % of tsunami are from submarine landslide?

• around 5%

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

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

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.

what can we do in trough arrives on shore first?

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

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

how does lack of warming impact region?

• difficult to disseminate info between and within countries

what is the time between waves?

• typic more than 30 mins

which waves are the worse?

• second or third waves often worse than first

rising water hazards

• boats carried inland as anchor and chains are lost

• larbors fill like bathtubs

water moving onshore issue

• vehicles, trees, and debris and tumbled and crushed

• buildings are crushed or carried off foundations

drawback from tsunamis?

• debris and sediment are tumbled and crushed

• sand stripped from beach

• human and animal fatalities occur at all stages

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

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

near-field tsunami warming system?

• arrival of tsunami less than 30 mins after tsunami trigger

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

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

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

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

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

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

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

Japan earthquake

• March 11 2011

• Magnitude 9.0 earthquake

• subduction zone earthquake

• generated a tsunamis that swept across the pacific ocean