Tsunami

TsunamiVelocityVery fast wave with a HUGE wavelength, triggered by a disturbance

LandslidesVolcanic eruptionsMeteor impactsEarthquakes

2004 Sumatra

2004 Sumatra

Lituya Bay, Alaska

Shallow- vs. Deep-water waves

Shallow- vs. Deep-water waves/2Deep

Shallow- vs. Deep-water wavesShallow

Shallow-water waves

ExampleD = 3,800 m (average depth)

Wind Waves vs. TsunamisWind Generated WavesTsunami Waves 5-20 seconds period 300-600 ft wave length10 kph speed

10 min-2 hr period Wave length HUGE (can be > 100 km)700 kph speed

E proportional to H2 Height. . . 500 greater!

Attenuation!!High frequency: trebleLow frequency: bass

Energy proportional to A2 v Little energy lost, so A2 v constant v decreases, A increasesAmplitudeVelocity

The Great Sumatra Tsunami of 2004MW = 9.3275,000 deadWaves up to 100 ft

Video of Sumatra Tsunami from Thai TV station

2004 Indonesia Tsunami

1964 Tsunami, Alaska

Banda Aceh:June 23rd 2004DigitalGlobe

Banda Aceh: December 28th 2004DigitalGlobe

Gleebrook Village:June 23rd 2004DigitalGlobe

DigitalGlobeGleebrook Village: December 28th 2004

Tsunami damage from:Force of water (in & out)Force of debrisFlooding (water damage)Flooding (crop damage)

What is it like to experience a tsunami?May be preceded by drop in water level Several waves, separated by 5 300 minutesFirst is rarely largestHilo, Hawaii Marigram

The Great ChileTsunami of 1960MW = 9.5Crossed oceanWaves up to 20 ft

The Great ChileTsunami of 1960Onagawa Japan

Onagawa, Japan, 19604:40 a.m.

Onagawa, Japan, 19604:45 a.m.

Onagawa, Japan, 19604:50 a.m.

Onagawa, Japan, 19607:30 a.m.

Tsunami coming ashore

Tsunami produced by landslides, eruptions, impactsDisturbance at surface size of disturbance several km much SMALLER than earthquake tsunamiAttenuates fasterCauses local damage only

Krakatoa, 1883

RI of Great Tsunami (ocean-wide effects)OceanRI (years)Pacific 12Caribbean15?Indian30?Atlantic10,000?

RI of Great Tsunami (ocean-wide effects)OceanRI (years)Pacific 12Caribbean15?Indian30?Atlantic10,000?

RI of Great Tsunami (ocean-wide effects)OceanRI (years)Pacific 12Caribbean15?Indian30?Atlantic1,000?

1918 Puerto Rico TsunamiMichael Count

1918 Puerto Rico TsunamiMichael Count

US risk of tsunamiHawaiiAlaskaPacific NWAtlantic coastGulf of Mexico

US risk of tsunamiHawaiiAlaskaPacific NWAtlantic coastGulf of Mexico

1964 Tsunami, Alaska

1964 Tsunami, Alaska

US risk of tsunamiHawaiiAlaskaPacific NWAtlantic coastGulf of Mexico

US risk of tsunamiHawaiiAlaskaPacific NWAtlantic coastGulf of Mexico

Atlantic Tsunami RiskClose Earthquake

Landslide

Submarine Volcano

Tele-tsunami(Slide from Maul, 2005)

1755 Lisbon Earthquake

Cumbre Vieja Volcano

?

The resulting tsunami?

US risk of tsunamiHawaiiAlaskaPacific NWAtlantic coastGulf of Mexico-negligible

Tsunami Hazard Mitigation

Evacuate shaded areasIsland of Hawaii

Example: Hilo, Hawaii

Warning siren

Global Seismologic Network

DART system buoy, Pacific Ocean

DART, DART II Systems (Deep Ocean Assessment and Reporting of Tsunami)DART Buoys12 deployed, others plannedAccurate to < 1mm!Collects every 15 sCost $250K + $50K annual maintenance

Planned DART buoys -

Proposed DART Locations

Tsunami wave height measured by satelitesGreat 2004 Sumatra tsunami wave 2 hours after quakeMeasuring from Space?

Philippines, Drill

Tsunami is a Japanese word meaning Harbor Wave. Thats not much better than the old English term, Tidal Wave. The truth is a tsunami is a special kind of wave: one with a HUGE wavelength. The huge wavelength, as we will learn, causes it to travel very fast. Tsunami waves are unusual, and are always triggered by some kind of disturbance of the water column.*The disturbances include landslides, volcanic eruptions, meteor impacts, and, most importantly, earthquakes. The vast majority of tsunami are caused by earthquakes.*This shows how an earthquake causes a disturbance of the water column causing a tsunami. Notice that the fault must have a vertical component (strike-slip faults wont do).*As the tsunami wave approaches shore it produces a large rise in water level, which causes the sea to wash inshore. The runup is the amount by which the water rises.*Tsunami-generating earthquakes must have: (a) a vertical component; and (b) be large. This shows the tsunami runup produced by various earthquakes. Notice that earthquakes need to be larger than about 7.3 in order to produce significant tsunami waves. The 2004 Sumatra tsunami was produced by an earthquake with M=9.3, and had an average runup of 12 meters (nearly 40 feet).*The MAXIMUM runup can be much larger than the average. Again, notice that earthquakes need to be larger than about M = 7.3 to produce significant runup. The 2004 Sumatra tsunami had a maximum runup of about 30 meters, or nearly 100 feet!*The largest runup ever recorded was from a landslide-generated tsunami in remote Lituya Bay, Alaska. A large portion of the hillsidse slid into the ocean and triggered a tsunami.*The tsunami runup was estimated by observing where the hillsidse was denuded of vegetation by the tsunami waveover 1,700 feet (1/3 mile!!). Luckily, no one lives in Lituya Bay.*Tsunami are special because they are always shallow-water waves. The distinction between shallow-water and deep-water waves is based on the motion induced by the passage of the wave relative to the depth of the sea. As a surface wave passes it causes the water molecules to follow circular paths. The radius of these circular paths decreases with depth until, at a depth = (wavelength) the water doesnt move at all. *The radius of these circular paths decreases with depth until, at a depth = (wavelength) the water doesnt move at all. *Deep-water waves are waves that only affect the top portion of the water column, because the wavelength is shorter than twice the depth. At depths greater than /2 the water doesnt even know about the passage of th3e wave. Shallow water waves are waves in which the wavelength is longer than twice the depth, so the entire water column is put in motion by the passage of the wave. *In detail, because of friction with the bottom of the sea, the path followed by water molecules in shallow-water waves is actually oblate.*Shallow-water waves are special. One important property is that their velocity depends ONLY on the depth, and is given by this equation. The constant g is the gravitational acceleration. The important thing to learn is that the velocity depends only on depth and increases as the depth increases.*You can use this formula to determine the speed at which a shallow-water wave will travel. For example, if a shallow-water wave is traveling over an ocean with a depth of 3,800 m (which is the average depth of the entire ocean) then it will travel at 700 km/h, or about as fast as a jet plane.

**Tsuanami waves are fundamentally different than normal, wind-driven waves. The most important difference is their wavelength, which may be on the order of hundreds of km, compared to wind-driven waves which have a wavelength on the order of a few hundred feet. Because of their enormous wavelength tsunami waves are everywhere shallow-water waves. Because they are shallow-water waves, their velocity depends only on the depth and, in the open ocean with great depths, they travel VERY fast, much, much faster than wind-driven waves. The period of the wave is related to the wavelength and velocity, and is much longer for tsunami waves.

The enormous wavelength of a tsunami wave changes its appearance as it nears shore. In comparison to a wind-driven wave, which arrives as a hill of water that quickly passes into a valley, a tsunami wave appears as a wall of water without end. There is a trough on the other side, but its many kilometers away.The energy carried by a tsunami wave is also much greater than a wind-driven waves (and thus its capacity to do damage). Energy is proportional to wave height H squared and the wavelength. The enormous wavelength of tsunami waves means they contain enormous energyapproximately 500 times greater than wind-driven waves.*Another property of tsunami waves is due to their enormous wavelengththeir ability to cross the oceans with little loss in energy. This is due to the fact that attenuation depends on wavelength (or frequency). Just like we discussed with earthquakes, waves with a lower frequency (or longer wavelength) attenuate less than waves with a high frequency (or short wavelength). Normal wind-driven waves attenuate rapidly, while tsunami waves attenuate very little. This allows them to travel great distances with little loss in amplitude and energy, and thus do damage many thousands of kilometers away from their origin.*In the open ocean tsunami waves have small amplitudes, on the order of one meter or less. You wouldnt even notice a tsunami wave passing beneath you on the open ocean. However, the wave piles up as it nears shore due to conservation of energy. Since energy is proportional to both amplitude and velocity, as the wave slows down its amplitude must rise. This happens with all waves, but is more important with tsunami waves because there is such a dramatic decrease in velocity.*This animation shows what happens to the amplitude of a wave as it shoals (nears shore).*Tsunami waves thus appear as a wall of water that may reach many tens of meters.*The most significant tsunami in the past 100 years occurred in 2004, in Indonesia. It was produced by a huge earthquake (M = 9.3) and killed over 250,000 people.*Tsunami waves radiated away from the fault that produced the earthquake and produced damage across the Indian Ocean.*This video shows what its like when the tsunami wave came ashore in Thailand, 100s of kms away from the epicenter. *The force of the tsunami wave knocked down buildings.*The salt water flooded croplands, destroying them and causing famine.*These before/after pictures show the extent of the devastation in Indonesia. The village of Banda Aceh was particularly hard-hit.*After.*Before*After.*Tsunami produce damage from the water wave itself, the debris carried by the water (which can include houses, beams, trees . . .), and well as flooding.*Tsunami arrive as a series of waves (usually less than 10). The first wave may be preceded by a drop in water level, as the trough arrives ahead of the crest. The first tsunami wave is rarely the largest (see marigram from Hilo Hawaii following the 1960 Chile earthquake).*The great Chile earthquake of 1960 was the largest earthquake ever recorded (M=9.5) and produced damage across the ocean.*Including in Japan!*Series of pictures showing the arrival of the tsunami waves. Note time.*Note how wave arrives as a wall of water.*Water still rising.*Next wave coming in.*Heres a video from Indonesia showing arrival of tsunami wave.*Tsunami may also be produced by disturbances to the water column caused by things falling in from above, such as landslides, volcanic eruptions, or meteors. The wavelength of the disturbance is approximately the size of the object, which means it is on t he order of several kmi.e., much smaller than wavelength produced by earthquake disturbances to the bottom of the water column. Smaller wavelength means waves attenuate faster, and therefore do not cause much damage far from source. Damage is local.*Example is 1883 eruption of volcano Krakatoa, in Indonesia. Volcano blasted a huge hole in volcano which caused water to rush in, causing a disturbance. Resulting tsunami killed 30,000+ on neighboring islands, but did not have a large effect at great distances.*The recurrence interval of tsunami is related to the frequency with which large (M>7.3) earthquakes occur in the ocean basin, or other events that can trigger tsunami (i.e., landslides, volcanic eruptions). The RI ranges from about 12 years for the Pacific to very long times (tens of thousands of years?) for the Atlantic.*Tsunami most frequently occur in the Pacific basin.*The Pacific has the shorted RI because it is rimmed with subduction zones capable of producing huge earthquakes. *The stars show the locations of major earthquakes within the past 50 years. Notice the one section that has lacked a major earthquake is the Cascade Subduction zone in the US Pacific Northwest. This is why tsunami risk is presently relatively high in this region.*Tsunami in the Caribbean are surprisingly common. *The Caribbean is a small plate tectonic plate. *Most Caribbean tsunami are relatively small and local caused by landslides or volcanic eruptions, or by earthquakes along the eastern edge of the Caribbean plate. **As an example, the 1918 Puerto Rico tsunami was caused by a landslide, and caused local damage.*Including runups of almost 20 feet on the western edge of Puerto Rico.In the US, the greatest tsunami risk occurs at Hawaii. Alaska and the Pacific NW also have a significant tsunami risk. The Atlantic coast and Gulf of Mexico have a very small risk.*Hawaii has a high risk because it is located in the middle of the Pacific Ocean, and is thus vulnerable to tsunami generated by earthquakes anywhere around the rim.*The 1960 tsunami caused large runups on Oahu (where Honolulu is). *The biggest problem occurred on the Big Island, where runup in Hilo bay was amplified due to its shape. Runups of over 35 feet occurred there.*Hawaii also experiences local tsunami due to huge landslides, as portions of the growing island periodically slide off into the sea. These landslides are fortunately rare, and havent happened in historic time.*The Aleutian peninsula of Alaska is also at risk for tsunami because it is a chain of islands built over a subduction zone.*Many large earthquakes have occurred here, producing tsunami. Fortunately, few people live in this area making the vulnerability low, and therefore the risk low.*The 1964 tsunami devastated coastal communities.*More from this tsunami.*The Pacific northwest has the third most tsunami risk.*This is due to the Cascadia subduction zone, which hasnt experienced a major earthquake in 1700.*The subduction zone here appears to be lockedi.e., not producing earthquakes. This is bad because the locked fault will eventually break, producing a massive earthquake.*The geometry of the subduction here is eerily similar to that of the Andaman fault in Indonesia which broke to produce the 2004 Sumatra tsunami. This suggests that a tsunami of similar size can be produced here.*This animation shows the simulated effects of such an earthquake and resultant tsunami.*The Atlantic coast has a relatively small tsunami risk, though media attention following the 2004 tsunami implied it was not zero.*The Atlantic basin has no subduction zones, which ought to make large earthquakes very rare.*If not large earthquakes, tsunami could be caused by smaller earthquakes (local effects), landslides, or volcanoes. Theres also some evidence that a subduction zone near Portugal could produce tele-tsunami (long-range effects due to earthquake tsunami).*The 1755 Lisbon earthquake was probably of M > 8, and produced widespread damage in Lisbon. The source of the earthquake is enigmatic.*Recent work suggests that a subduction zone exists between the Iberian Peninsula and Africa, which could generate large earthquakes and tsunami, and might have been responsible for creating the Lisbon earthquake.*The most popular source for an Atlantic tsunami is the volcanic island of Las Palmas, in the Canary Island chain, and its volcano Cumbre Vieja.*Landslides periodically slide off of Cumbre Vieja. Some geologists have suggested that a large block is likely to fail soon. Such a landslide could generate a tsunami.*Early modeling (made popular by a NOVA episode) suggested that such a tsunami would cause devastating waves to wash up on the populated eastern US coastline, causing widespread devastation. It is more likely that any tsunami waves would attenuate quickly, since the wavelength would be small. Therefore it is possible that a tsunami could damage the Canary Islands, and even perhaps portions of eastern Africa, but it is unlikely that such a tsunami could do more than produce a few cm of water rise on the eastern US seaboard.*The Aleutian peninsula of Alaska is also at risk for tsunami because it is a chain of islands built over a subduction zone.*Since theres no way to prevent tsunami, mitigation emphasizes warning and zoning.*Zoning and evacuation zones are useful in areas prone to tsunami, such as Hawaii.*The land surrounding Hilo Bay, for example, has been converted to mostly parkland because of tsunami risk.*This waterfront park was formed in the aftermath of the 1960 tsunami. Previously it contained many buildings that were destroyed by the 1960 tsunami.*Tsunami warning systems depend on recognition and broadcasting of warnings. In many cases, effecting the evacuation is the hardest part.*Identification of tsunami waves starts with the global seismologic network of linked seismographs. These are capable of identifying and locating large earthquakes worldwide in a matter of minutes.*Once a possible tsunami-generating earthquake has been recorded, the next step is to determine whether a tsunami wave has actually been generated. Only a few of the many large earthquakes that happen worldwide every year actually generate tsunami. The recognition of tsunami waves depends on specially designed open-ocean buoys, called DART buoys. *DART stands for deep ocean assessment and reporting of tsunami. This animation shows how they work. They very precisely measure the pressure at the bottom of the ocean, and convert this pressure to wave height. They are capable of detecting the passage of a tsunami wave with an amplitude of just a few cm.*The Pacific Ocean is well-lined with DART buoys, and more are arriving for the Atlantic, Caribbean, and Indian Oceans.*Unfortunately, there were no DART buoys in the Indian Ocean in 2004, but there are now.**In the future, it may also be possible to detect tsunami waves from space. The 2004 tsunami happened to coincide with a satellite flyover that permitted calculation of the sea surface elevation, and thus the tsunami wave.*Once a tsunami wave has been positively identified, warnings go out to places in advance of the wave. These are tsunami sirens in Hawaii.*People not only need to know a tsunami wave is coming, they also need to know where to go. Often people have many hours of advance warning, so it is possible to evacuate everyone in harms way.*This is the new tsunami evacuation route for Indonesia.*In all cases, people have to practice so that they can evacuate quickly. This is a tsunami evacuation drill in the Philippines.*