Tsunami Facts and Information
Here's everything you need to know about tsunamis and how the waves are formed. 6 days ago These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate. Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the.
As a tsunami leaves the deep water of the open-ocean and travels into the shallower water near the coast, it transforms. If you read the "The physics of a tsunami" section, you will know that a tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows.
The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed diminishes, its height grows. This is called shoaling. Because of this shoaling effect, a tsunami that is unnoticeable at sea, may grow to be several metres or more in height near the coast. The increase of the tsunami's waveheight as it enters shallow water is given by: So a tsunami with a height of 1 m in the open ocean where the water depth is m would have a waveheight of 4 to 5 m in water of depth 10 m.
Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence.
Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Depending on whether the first part of the tsunami to reach the shore is a crest or a trough, it may appear as a rapidly rising or falling tide. Local bathymetry may also cause the tsunami to appear as a series of breaking waves. Tsunamis have great erosion potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundating, or flooding, hundreds of metres inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures.
Tsunamis may reach a maximum vertical height onshore above sea level, often called a run-up height, of tens of metres. How are tsunamis measured or observed? In the deep ocean, a tsunami has a small amplitude less than 1 metre but very long wavelength hundreds of kilometres. This means that the slope, or steepness of the wave is very small, so it is practically undetectable to the human eye. However, there are ocean observing instruments that are able to detect tsunamis. Tide Gauges Tide gauges measure the height of the sea-surface and are primarily used for measuring tide levels.
What is the difference between a tsunami and a tidal wave?
These consist of an acoustic sensor connected to a vertical tube open at the lower end which is in the water.
The acoustic sensor emits a sound pulse which travels from the top of the tube down to the water surface, and is then reflected back up the tube. The distance to the water level can then be calculated using the travel time of the pulse. This system filters out small-scale effects like wind-waves and has the capacity to measure sea-level changes within 1mm accuracy.
The tide gauge at Cocos Island observed the tsunami on December 26th as it passed by the island, as shown in these observations made during December. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves.
As early as BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen.
Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Movement on normal extensional faults can also cause displacement of the seabed, but only the largest of such events typically related to flexure in the outer trench swell cause enough displacement to give rise to a significant tsunami, such as the Sumba and Sanriku events.
Plate slips, causing subsidence and releasing energy into water. The energy released produces tsunami waves.
They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.
On April 1,the 8. Between and were killed. The area where the earthquake occurred is where the Pacific Ocean floor is subducting or being pushed downwards under Alaska. Examples of tsunami originating at locations away from convergent boundaries include Storegga about 8, years ago, Grand BanksPapua New Guinea Tappin, The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into the ocean and generate a tsunami.
They dissipated before travelling transoceanic distances.
What is the difference between a tsunami and a tidal wave?
The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates methane etc. The Valdivia earthquake Mw 9. Landslides In the s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant submarine landslides.
These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. Their existence was confirmed inwhen a giant landslide in Lituya BayAlaska, caused the highest wave ever recorded, which had a height of metres over feet. Two people fishing in the bay were killed, but another boat managed to ride the wave.
Another landslide-tsunami event occurred in when a massive landslide from Monte Toc entered the Vajont Dam in Italy. Around 2, people died. Some geologists claim that large landslides from volcanic islands, e. Cumbre Vieja on La Palma in the Canary Islandsmay be able to generate megatsunamis that can cross oceans, but this is disputed by many others.
Californians, for instance, are unlikely to be shocked if they feel the ground shuddering beneath their feet. But a draft map released by the U. More than years of earthquakes glow on a world map.
Earthquakes & Tsunamis: Causes & Information
Preparing for disaster Scientists have not yet come up with a way to forecast earthquakes. Although animals are reputed to have a sixth sense when it comes to these vibrations, no research has confirmed it, much less determined how such predictions might occur. In many cases, animals are simply sensing the arrival of earthquake waves that go unnoticed by people.
However, scientists can identify locations that are likely to experience earthquakes in the future. For instance, along the tectonic plate boundary off the western shore of South America, researchers have mapped the location of historical earthquakes and found " seismic gaps " — zones with no recent large earthquake quakes. And indeed, scientists had forecast a major earthquake in a seismic gap near Maule, Chile, which was hit by a magnitude Even without such forecasts, there are some basic things that can be done to prepare for an earthquake.
- Tsunami Facts and Information
The Federal Emergency Management Agency recommends that all families everywhere should have an emergency kit in their home and car, and communicate with your loved ones a plan for any type of disaster not just for earthquakes. Such preparation can make a difference not only physically, but also emotionally. Keep heavy objects away from beds and sitting areas, and fasten fixtures such as large televisions to the walls.
Locate a safe place in each room, under a sturdy desk or table, where you can seek refuge from falling objects. If you are outside, get into an open area, away from structures or bridges.
According to FEMA, many deaths in the Long Beach earthquake occurred when people ran outside, only to be crushed by falling debris from collapsing structures. Remember that the shaking ground rarely causes injury or death; instead, it is the falling objects that result from the quake.
If you are in a car, stop as soon as you are able, but stay inside the car. If you are at or near the beach, move quickly inland to avoid potential waves from tsunamis. After an earthquake, proceed with caution.
Remember that most earthquakes are generally followed by aftershocks. Keep an eye and a nose out for gas leaks.