a tsunami...? i am confused...please educate me.?

Question

i just read a news article which stated that alaska had a 4-inch tsunami, as the result of a quake near japan (which also caused "small waves" for them).

here is the link if you want to look:
http://cbs13.com/topstories/topstories_story_013000218.html

does alaska have such small waves that a 4-inch wave meets "tsunami standards"?

the article goes on to say that other "warnings" to other areas were called off, but pertaining to alaska...this wave was labeled a "tsunami", not a "tsunami warning" it was even impressive enough to make the "top stories" section!

this really is a serious question to what i think makes the news and seizmologists look stupid.

can anyone tell me why this 4-inch alaskan wave was determined to be a tsunami? why not the one before it, or after it?

thanks.

excuse me...i did misread it.
it was UNDER 4 inches.
.

jack the lad...sorry. i'll use smaller words next time.

Answer 1

It seems that the point of the article was that they did record the expected tsunami, and its magnitude was only 4', meaning people farther away from the quake had nothing to worry about.

The tsunami generated by the 1974 Adak, AL earthquake did considerable damage in Anchorage accompanied, I believe with some deaths. There was damage as far south as Oregon.

Answer 2

Maybe it was the distance the tsunami travelled that was unique. Japan to Alaska. A tsunami doesn't have to be huge but it is produced by an earthquake.
I know where your coming from, these guys are are square though and maybe for them this is really exciting!

Answer 3

A tsunami is a wave caused by an earthquake. It can be any size. It is difficult to predict size with accuracy (presumably because of issues like direction of flow, angle of approach to beach, local tides and currents etc). I dont think Alaska has small waves, but they had to issue a warning because you only get one go at seeing it!

Answer 4

When Krakatoa erupted over 100 years ago and caused a huge tsunami......it was only 2" high when it reached our shoreline!
Alaska often experiences tsunamis because of the major faultlines located off Japan.

Answer 5

tsunami is the hawian word for tidal wave, now it is widely used among the western news offices as it sounds more effective and dramatic

Answer 6

A tsunami (pronounced /tsʊˈnɑːmi/ or /sʊˈnɑːmi/) is a series of waves created when a body of water, such as an ocean is rapidly displaced on a massive scale. Earthquakes, mass movements above or below water, volcanic eruptions and other underwater explosions, landslides and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating. The term tsunami comes from the Japanese language meaning harbour ("tsu", 津) and wave ("nami", 波). Although in Japanese tsunami is used for both the singular and plural, in English tsunamis is often used as the plural. The term was created by fishermen who returned to port to find the area surrounding their harbour devastated, although they had not been aware of any wave in the open water. Tsunamis are common throughout Japanese history, approximately 195 events in Japan have been recorded.

A tsunami has a much smaller amplitude (wave heights) offshore, and a very long wavelength (often hundreds of kilometres long), which is why they generally pass unnoticed at sea, forming only a passing "hump" in the ocean. Tsunamis have been historically referred to as tidal waves because as they approach land, they take on the characteristics of a violent onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean (with which people are more familiar). Since they are not actually related to tides the term is considered misleading and its usage is discouraged by oceanographers. [1] Since not all tsunamis occur in harbours, however, that term is equally misleading, although it does have the benefit of being misleading in a different language

Causes

Generation of a tsunamiTsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis.

Submarine landslides (which are sometimes triggered by large earthquakes) as well as collapses of volcanic edifices may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and form a tsunami.

Tsunamis are surface gravity waves that are formed as the displaced water mass moves under the influence of gravity and radiate across the ocean like ripples on a pond.

In the 1950s it was discovered that larger tsunamis than previously believed possible could be caused by landslides, explosive volcanic action, and impact events. These phenomena rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Tsunamis caused by these mechanisms, unlike the ocean-wide tsunamis caused by some earthquakes, generally dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected. These events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay which produced a water wave estimated at 50 – 150 m and reached 524 m up local mountains. However, an extremely large landslide could generate a megatsunami that might have ocean-wide impacts.

The geological record tells us that there have been massive tsunamis in Earth's past. These tsunamis were so large that they caused landslides on the opposite coast triggering another massive tsunami, or "bounce back" tsunami. An example today would be a landslide equivalent to everything west of Portland (Oregon, USA) falling in to the Pacific ocean, resulting in a tsunami that would then hit the Chinese coast with enough force to erode the coast, triggering a landslide large enough to send a tsunami that would in turn inundate the US west coast and would wipe out Portland.

Characteristics

There is a common misconception that tsunamis behave like wind-driven waves or swells (with air behind them, as in this celebrated 19th century woodcut by Hokusai). In fact, a tsunami is better understood as a new and suddenly higher sea level, which manifests as a shelf or shelves of water. The leading edge of a tsunami superficially resembles a breaking wave but behaves differently: the rapid rise in sea lev, combine with the weight and pressure of the ocean behind it, has far greater force.Often referred to as "tidal waves", a tsunami does look like the popular impression of "a normal wave, only much bigger". Instead it looks rather like an endlessly onrushing tide which forces its way around and through any obstacle. Most of the damage is caused by the huge mass of water behind the initial wave front, as the height of the sea keeps rising fast and floods power in the coastal area. The sheer weight of water is enough to pulverize objects in its path, often reducing buildings to their foundations and scouring exposed ground to the bedrock. Large objects such as ships and boulders can be carried several miles inland before the tsunami subsides. XP

Tsunamis act very differently from typical surf swells: they contain immense energy, propagate at high speeds and can travel great trans-oceanic distances with little overall energy loss. A tsunami can cause damage thousands of kilometres from its origin, so there may be several hours between its createand its impacton a coastarriving long after the seismic wave generated by the originating event arrives. Although the total or overall loss of energy is small, the total energy is spread over a larger and larger circumference as the wave travels. The energy per linear metre in the wave proportional to the inverse of the distance from the source.[citation needed] (In other words, it decreases linearly with distance.) This is the two-dimensional equivalent of the inverse square law, which is obeyed by waves which propagate in three dimensions (in a sphere instead of a circle).

A single tsunami event may involve a series of waves of varying heights; so the set of waves is called a train. In open water, tsunamis have extremely long periods (the time for the next wave top to pass a point after the previous one), from minutes to hours, and long wavelengths of up to several hundred kilometres. This is very different from typical wind-generated swells on the ocean, which might have periods of about 10 seconds and wavelengths of 150 metres.

The height of a tsunami wave in open water is often less than one metre, and the height is spread over the wavelength of the tsunami which is multiple kilometres. This is unnoticeable to people on ships in deep water. Because it has such a large wavelength, the energy of a tsunami mobilizes the entire water column down to the sea bed. Typical ocean surface waves in deep water cause water motion to a depth equal to half their wavelength. This means that ocean surface wave motion will only reach down to a depth of a few 100 m or less. Tsunamis, by contrast, behave as 'shallow water waves' in the deep ocean.

Because a tsunami behaves like a 'shallow water wave,' its speed is based on the depth of the water. Typically, a tsunami wave will travel across a deep ocean at an average speed of 400 to 500 mph.([2]). As the wave approaches land, the sea shallows and the tsunami wave no longer travels as quickly, so it begins to 'pile-up'; the wave-front becomes steeper and taller, and there is less distance between crests. While a person at the surface of deep water would probably not even notice the tsunami, the wave can increase to a height of six stories or more as it approaches the coastline and compresses. The steepening process is analogous to the cracking of a tapered whip. As a wave goes down the whip from handle to tip, the same energy is carried by less and less material, which as a consequence then moves more violently.

A wave becomes a 'shallow-water wave' when the ratio between the water depth and its wavelength gets very small, and since a tsunami has an extremely large wavelength (hundreds of kilometres), tsunamis act as a shallow-water wave even in deep oceanic water. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s2) and the water depth. For example, in the Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200 m/s (720 km/h or 450 mph) with little energy loss, even over long distances. At a water depth of 40 m, the speed would be 20 m/s (about 72 km/h or 45 mph), which is much slower than the speed in the open ocean but the wave would still be difficult to outrun.

Tsunamis propagate outward from their source, so coasts in the "shadow" of affected land masses are usually fairly safe. However, tsunami waves can diffract around land masses (as shown in this Indian Ocean tsunami animation as the waves reach southern Sri Lanka and India). They are also not necessarily symmetrical; tsunami waves may be much stronger in one direction than another, depending on the nature of the source and the surrounding geography.

Local geographic peculiarities can lead to seiche or standing waves forming, which can amplify the onshore damage. For instance, the tsunami that hit Hawaii on April 1, 1946 had a fifteen-minute interval between wave fronts. The natural resonant period of Hilo Bay is about thirty minutes. That meant that every second wave was in phase with the motion of Hilo Bay, creating a seiche in the bay. As a result, Hilo suffered worse damage than any other place in Hawaii, with the tsunami/seiche reaching a height of 14 m and killing 159 inhabitants.

There is more information just visit the web-site below.

http://en.wikipedia.org/wiki/Tsunami

Fares Alsagri

Answer 7

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