Main article: Historic tsunami
Historically speaking, tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia-Pacific region - particularly Japan. The Boxing Day Tsunami in 2004 caused approx. 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued rightly that it could only be explained as a consequence of ocean earthquakes.[1] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[2]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. 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.[3]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) describes the typical sequence of a tsunami including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave on the occasion of the 365 A.D. tsunami devastating Alexandria.[4] [5]
Tuesday, May 20, 2008
Tsunami and Bible
Main article: Historic tsunami
Historically speaking, tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia-Pacific region - particularly Japan. The Boxing Day Tsunami in 2004 caused approx. 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued rightly that it could only be explained as a consequence of ocean earthquakes.[1] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[2]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. 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.[3]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) describes the typical sequence of a tsunami including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave on the occasion of the 365 A.D. tsunami devastating Alexandria.[4] [5]
Historically speaking, tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia-Pacific region - particularly Japan. The Boxing Day Tsunami in 2004 caused approx. 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued rightly that it could only be explained as a consequence of ocean earthquakes.[1] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[2]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. 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.[3]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) describes the typical sequence of a tsunami including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave on the occasion of the 365 A.D. tsunami devastating Alexandria.[4] [5]
Tsunami in History
Main article: Historic tsunami
Historically speaking, tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia-Pacific region - particularly Japan. The Boxing Day Tsunami in 2004 caused approx. 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued rightly that it could only be explained as a consequence of ocean earthquakes.[1] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[2]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. 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.[3]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) describes the typical sequence of a tsunami including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave on the occasion of the 365 A.D. tsunami devastating Alexandria.[4] [5]
Historically speaking, tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia-Pacific region - particularly Japan. The Boxing Day Tsunami in 2004 caused approx. 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued rightly that it could only be explained as a consequence of ocean earthquakes.[1] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[2]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. 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.[3]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) describes the typical sequence of a tsunami including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave on the occasion of the 365 A.D. tsunami devastating Alexandria.[4] [5]
Warnings and Prevention
There is often no advance warning of an approaching tsunami. However, since earthquakes are often a cause of tsunami, any earthquake occurring near a body of water may generate a tsunami if it occurs at shallow depth, is of moderate or high magnitude, and the water volume and depth is sufficient. In Japan moderate - 4.2 Magnitude earthquakes can generate tsunami which can inundate the area within 15 minutes.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.
80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.
80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
Signs of an approaching tsunami
There is often no advance warning of an approaching tsunami. However, since earthquakes are often a cause of tsunami, any earthquake occurring near a body of water may generate a tsunami if it occurs at shallow depth, is of moderate or high magnitude, and the water volume and depth is sufficient. In Japan moderate - 4.2 Magnitude earthquakes can generate tsunami which can inundate the area within 15 minutes.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.
80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.
80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
Causes
A tsunami can be generated when converging or destructive plate boundaries abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent (constructive) or conservative plate boundaries. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis.
On 1st April, 1946 a Magnitude 7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.
Examples of tsunami being generated at locations away from convergent boundaries include - Storegga during the Neolithic era, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). In the case of the Grand Banks and Papua New Guinea tsunamis an earthquake caused sediments to become unstable and subsequently fail. These slumped and as they flowed down slope a tsunami was generated. These tsunami did not travel transoceanic distances.
It is not known what caused the Storegga sediments to fail. It may have been due to overloading of the sediments causing them to become unstable and they then failed solely as a result of being overloaded. It is also possible that an earthquake caused the sediments to become unstable and then fail. Another theory is that a release of gas hydrates (methane etc.,) caused the slump.
The "Great Chilean earthquake" (19:11 hrs UTC) 22nd May 1960 (9.5 Mw), the 27th March 1964 "Good Friday earthquake" Alaska 1964 (9.2 Mw), and the "Great Sumatra-Andaman earthquake" (00:58:53 UTC) 26th December 2004 (9.2 Mw), are recent examples of powerful megathrust earthquakes that generated a tsunami that was able to cross oceans. Smaller (4.2 Mw) earthquakes in Japan can trigger tsunami that can devastate nearby coasts within 15 minutes or less.
In the 1950s it was hypothesised that larger tsunamis than had previously been believed possible may be caused by landslides, explosive volcanic action e.g., Santorini, Krakatau, and impact events when they contact water. 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 at a rate faster than the ocean water can absorb it. They have been named by the media as "mega-tsunami."
Tsunami caused by these mechanisms, unlike the trans-oceanic tsunami caused by some earthquakes, may 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 1958, which produced a wave with an initial surge estimated at 524m. However, an extremely large gravitational landslide might generate a so called "mega-tsunami" that may have the ability to travel trans-oceanic distances. This though is strongly debated and there is no actual geological evidence to support this hypothesis.
On 1st April, 1946 a Magnitude 7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.
Examples of tsunami being generated at locations away from convergent boundaries include - Storegga during the Neolithic era, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). In the case of the Grand Banks and Papua New Guinea tsunamis an earthquake caused sediments to become unstable and subsequently fail. These slumped and as they flowed down slope a tsunami was generated. These tsunami did not travel transoceanic distances.
It is not known what caused the Storegga sediments to fail. It may have been due to overloading of the sediments causing them to become unstable and they then failed solely as a result of being overloaded. It is also possible that an earthquake caused the sediments to become unstable and then fail. Another theory is that a release of gas hydrates (methane etc.,) caused the slump.
The "Great Chilean earthquake" (19:11 hrs UTC) 22nd May 1960 (9.5 Mw), the 27th March 1964 "Good Friday earthquake" Alaska 1964 (9.2 Mw), and the "Great Sumatra-Andaman earthquake" (00:58:53 UTC) 26th December 2004 (9.2 Mw), are recent examples of powerful megathrust earthquakes that generated a tsunami that was able to cross oceans. Smaller (4.2 Mw) earthquakes in Japan can trigger tsunami that can devastate nearby coasts within 15 minutes or less.
In the 1950s it was hypothesised that larger tsunamis than had previously been believed possible may be caused by landslides, explosive volcanic action e.g., Santorini, Krakatau, and impact events when they contact water. 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 at a rate faster than the ocean water can absorb it. They have been named by the media as "mega-tsunami."
Tsunami caused by these mechanisms, unlike the trans-oceanic tsunami caused by some earthquakes, may 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 1958, which produced a wave with an initial surge estimated at 524m. However, an extremely large gravitational landslide might generate a so called "mega-tsunami" that may have the ability to travel trans-oceanic distances. This though is strongly debated and there is no actual geological evidence to support this hypothesis.
Terminology
The term tsunami comes from the Japanese meaning harbor ("tsu", 津) and wave ("nami", 波). [a. Jap. tsunami, tunami, f. tsu harbour + nami waves. - Oxford English Dictionary]. For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in Japanese. Tsunamis are common throughout Japanese history; approximately 195 events in Japan have been recorded.
A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 mm above the normal sea surface. A tsunami can occur at any state of the tide and even at low tide will still inundate coastal areas if the incoming waves surge high enough.
Tsunamis are often referred to popularly as tidal waves. This term is inaccurate because tsunamis are not related to tides and its use is discouraged by geologists and oceanographers; however, it is worth noting that the term tsunami is no more accurate because tsumanis are not limited to harbours.
A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 mm above the normal sea surface. A tsunami can occur at any state of the tide and even at low tide will still inundate coastal areas if the incoming waves surge high enough.
Tsunamis are often referred to popularly as tidal waves. This term is inaccurate because tsunamis are not related to tides and its use is discouraged by geologists and oceanographers; however, it is worth noting that the term tsunami is no more accurate because tsumanis are not limited to harbours.
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