Tsunami

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?

*

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