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102-542: Exposed to the open Pacific, Alberni Inlet has been subject to tsunamis . The largest in historic times was the result of the Good Friday earthquake in Alaska in 1964, and destroyed part of downtown Port Alberni. The narrow inlet amplified the size and intensity of the wave, and when it struck the two towns it had a height of 2.4 metres (8 ft). One hour later, a second, larger wave of 3.0 metres (10 ft) hit. It

204-417: A megathrust earthquake since January 26, 1700. Despite low levels of seismicity compared to other subduction zones, Cascadia hosts various types of earthquakes that are recorded by seismic and geodetic instruments, such as seismometers and GNSS receivers . Tremor, a type of slow fault slip , occurs along almost the entire length of Cascadia at regular intervals of 13–16 months. Tremor occurs deeper on

306-430: 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, 1946, the 8.6 M w   Aleutian Islands earthquake occurred with a maximum Mercalli intensity of VI ( Strong ). It generated a tsunami which inundated Hilo on the island of Hawaii with a 14-metre high (46 ft) surge. Between 165 and 173 were killed. The area where

408-558: A 50 kilometer by 300 kilometer (about 30 mile by 200 mile) area. The movement was the equivalent of a 6.7 magnitude earthquake. The motion did not trigger an earthquake and was only detectable as silent, non-earthquake seismic signatures. In 2004, a study conducted by the Geological Society of America analyzed the potential for land subsidence along the Cascadia subduction zone. It postulated that several towns and cities on

510-532: A canal; for they figure that Alberni Canal is something similar to Manchester Canal, Panama Canal and Suez Canal, where extra fees for pilotage, canal dues, extra insurance and so forth come into the question." The name change was officially approved in 1945. Other inlets on the Northwest Coast continue to use "canal" names including Lynn Canal , Portland Canal and Hood Canal . Alberni Inlet extends into Vancouver Island from Barkley Sound, an inlet of

612-427: A few minutes at a time. The Tauredunum event was a large tsunami on Lake Geneva in 563 CE, caused by sedimentary deposits destabilised by a landslide. In the 1950s, it was discovered that tsunamis larger than had previously been believed possible can be caused by giant submarine landslides . These large volumes of rapidly displaced water transfer energy at a faster rate than the water can absorb. Their existence

714-432: A huge wave. As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its speed decreases below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its amplitude grows enormously—in accord with Green's law . Since the wave still has the same very long period , the tsunami may take minutes to reach full height. Except for

816-541: A large problem of awareness and preparedness, as exemplified by the eruption and collapse of Anak Krakatoa in 2018 , which killed 426 and injured thousands when no warning was available. It is still regarded that lateral landslides and ocean-entering pyroclastic currents are most likely to generate the largest and most hazardous waves from volcanism; however, field investigation of the Tongan event , as well as developments in numerical modelling methods, currently aim to expand

918-519: A layer of marsh followed by a layer of sand. Jody Bourgeois and her team went on to demonstrate that the sand cover had originated with a tsunami surge rather than a storm surge. In 1995, an international team led by Alan Nelson of the USGS further corroborated these findings with 85 new samples from the rest of the Pacific Northwest . All along British Columbia, Washington State, and Oregon,

1020-564: A magnitude 6.7 earthquake in Seattle would result in 7,700 dead and injured, $ 33 billion in damage, 39,000 buildings severely damaged or destroyed, and 130 simultaneous fires. The Cascade Volcanic Arc is a continental volcanic arc that extends from northern California to the coastal peninsula of Alaska . The arc consists of a series of Quaternary age stratovolcanoes that grew on top of pre-existing geologic materials that ranged from Miocene volcanics to glacial ice . The Cascade Volcanic arc

1122-538: A massive landslide from Monte Toc entered the reservoir behind the Vajont Dam in Italy. The resulting wave surged over the 262-metre (860 ft)-high dam by 250 metres (820 ft) and destroyed several towns. Around 2,000 people died. Scientists named these waves megatsunamis . Some geologists claim that large landslides from volcanic islands, e.g. Cumbre Vieja on La Palma ( Cumbre Vieja tsunami hazard ) in

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1224-543: A megathrust earthquake is proportional to length of the rupture along the fault. The Cascadia subduction zone, which forms the boundary between the Juan de Fuca and North American plates, is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. Because of the great length of the fault, the Cascadia subduction zone is capable of producing very large earthquakes if rupture occurs along its entire length. Thermal and deformation studies indicate that

1326-577: A reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run-up. About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. However, tsunami interactions with shorelines and the seafloor topography are extremely complex, which leaves some countries more vulnerable than others. For example,

1428-462: A ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at the shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However, if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. The drawback can exceed hundreds of metres, and people unaware of

1530-467: A significant tsunami, such as the 1977 Sumba and 1933 Sanriku events. Tsunamis have a small wave height offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in

1632-424: A sudden inundation of salt water had killed them hundreds of years ago. Originally thought to have died slowly due to a gradual rise in sea level, closer inspection yielded a different story: the land plummeted up to two meters during an earthquake. Having initially tested spruce using tree-ring dating , they found that the stumps were too rotted to count all the outer rings. However, upon having examined those of

1734-655: A transoceanic tsunami has not occurred within recorded history. Susceptible locations are believed to be the Big Island of Hawaii , Fogo in the Cape Verde Islands , La Reunion in the Indian Ocean , and Cumbre Vieja on the island of La Palma in the Canary Islands ; along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on

1836-445: A tsunami can be calculated by obtaining the square root of the depth of the water in metres multiplied by the acceleration due to gravity (approximated to 10 m/s ). For example, if the Pacific Ocean is considered to have a depth of 5000 metres, the velocity of a tsunami would be √ 5000 × 10 = √ 50000 ≈ 224 metres per second (730 ft/s), which equates to a speed of about 806 kilometres per hour (501 mph). This

1938-434: A tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. 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

2040-473: A tsunami, which is that of an extraordinarily high tidal bore . Tsunamis and tides both produce waves of water that move inland, but in the case of a tsunami, the inland movement of water may be much greater, giving the impression of an incredibly high and forceful tide. In recent years, the term "tidal wave" has fallen out of favour, especially in the scientific community, because the causes of tsunamis have nothing to do with those of tides , which are produced by

2142-467: Is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake . Earthquakes , volcanic eruptions and underwater explosions (including detonations, landslides , glacier calvings , meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind , or tides , which are in turn generated by

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2244-620: Is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island. Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. Of historical and current (with regard to risk assumptions) importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores–Gibraltar Transform Fault ), the 1783 Calabrian earthquakes , each causing several tens of thousands of deaths and

2346-562: Is also used to refer to the phenomenon because the waves most often are generated by seismic activity such as earthquakes. Prior to the rise of the use of the term tsunami in English, scientists generally encouraged the use of the term seismic sea wave rather than tidal wave . However, like tidal wave , seismic sea wave is not a completely accurate term, as forces other than earthquakes—including underwater landslides , volcanic eruptions, underwater explosions, land or ice slumping into

2448-423: Is cut by an 88 m (289 ft) deep channel allowing for water exchange between the sound and the outer basin. Despite the shallow depth of the sill midway up the inlet, deep water in both basins is renewed annually, a process driven by upwelling in the ocean to the west of Vancouver Island. The Somass River enters at Port Alberni near the inlet's terminus. Numerous small streams enter it on both sides along

2550-496: Is designed to help accurately forecast the passage of tsunamis across oceans as well as how tsunami waves interact with shorelines. The term "tsunami" is a borrowing from the Japanese tsunami 津波 , meaning "harbour wave." For the plural, one can either follow ordinary English practice and add an s , or use an invariable plural as in the Japanese. Some English speakers alter the word's initial / ts / to an / s / by dropping

2652-600: Is located approximately 100 km inland from the coast, and forms a north-to-south chain of peaks that average over 3,000 m (10,000 ft) in elevation. The major peaks from south to north include: The most active volcanoes in the chain include Mount St. Helens, Mount Baker, Lassen Peak, Mount Shasta, and Mount Hood. Mount St. Helens captured worldwide attention when it erupted catastrophically in 1980 . St. Helens continues to rumble, albeit more quietly, emitting occasional steam plumes and experiencing small earthquakes, both signs of continuing magmatic activity. Most of

2754-824: Is monitored by the Pacific Northwest Seismic Network 's semi-automatic tremor detection system. The majority of interplate earthquakes , or earthquakes that occur near the boundaries of tectonic plates, near the Cascadia subduction zone occur in the forearc of the overriding North American plate in Washington, west of the Cascade Volcanic Arc and east of where tremor occurs. These earthquakes are sometimes referred to as crustal earthquakes, and they are capable of causing significant damage due to their relatively shallow depths. A damaging magnitude 7 interplate earthquake occurred on

2856-401: Is most important for the foreign trade existing between Port Alberni and the outside world, that this word canal, which is greatly mistaken, should be changed for the proper word of inlet. It is needless to tell you that a great difficulty of this word canal comes in with the foreign shipping in general, who figure themselves the extra expense and the danger attached to sending their ships through

2958-515: Is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis. Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called " wave train ". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami

3060-791: Is now Shakespear Regional Park at the tip of the Whangaparāoa Peninsula in the Auckland Region of New Zealand ; the attempt failed. There has been considerable speculation about the possibility of using nuclear weapons to cause tsunamis near an enemy coastline. Nuclear testing in the Pacific Proving Ground by the United States generated poor results. In Operation Crossroads in July 1946, two 20-kilotonne-of-TNT (84 TJ) bombs were detonated, one in

3162-625: Is now mostly subducted under the North American plate. The North American plate itself is moving slowly in a generally southwest direction, sliding over the smaller plates as well as the huge oceanic Pacific plate (which is moving in a northwest direction) in other locations such as the San Andreas Fault in central and southern California. Tectonic processes active in the Cascadia subduction zone region include accretion , subduction , deep earthquakes , and active volcanism of

Alberni Inlet - Misplaced Pages Continue

3264-551: Is on a low sand beach about halfway along the inlet's eastern shore. In 1931 there was a recommendation that the name be changed from canal to inlet so that foreign shippers would not mistake it for a canal. As described by the BC Geographical Names Information System: First labelled Canal de Alberni on Spanish charts. In 1931 H.D.Parizeau, Hydrographic Service recommended that the ambiguous term 'canal' be changed to 'inlet', "...it

3366-426: Is the formula used for calculating the velocity of shallow-water waves. Even the deep ocean is shallow in this sense because a tsunami wave is so long (horizontally from crest to crest) by comparison. The reason for the Japanese name "harbour wave" is that sometimes a village's fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated by

3468-565: The 1700 Cascadia earthquake . Orally transmitted legends from the Olympic Peninsula area tell of an epic battle between a thunderbird and a whale . In 2005, seismologist Ruth Ludwin set out to collect and analyze anecdotes from various First Nations groups. Reports from the Huu-ay-aht , Makah , Hoh , Quileute , Yurok , and Duwamish peoples referred to earthquakes and saltwater floods. This collection of data allowed

3570-430: The 1883 eruption of Krakatoa , and the 2022 Hunga Tonga–Hunga Ha'apai eruption . Over 20% of all fatalities caused by volcanism during the past 250 years are estimated to have been caused by volcanogenic tsunamis. Debate has persisted over the origins and source mechanisms of these types of tsunamis, such as those generated by Krakatoa in 1883, and they remain lesser understood than their seismic relatives. This poses

3672-688: The 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the deadliest natural disasters in modern Europe. 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 426 BC the Greek historian Thucydides inquired in his book History of

3774-413: The Canary Islands , may be able to generate megatsunamis that can cross oceans, but this is disputed by many others. In general, landslides generate displacements mainly in the shallower parts of the coastline, and there is conjecture about the nature of large landslides that enter the water. This has been shown to subsequently affect water in enclosed bays and lakes, but a landslide large enough to cause

3876-556: The Cascades . This volcanism has included such notable eruptions as Mount Mazama ( Crater Lake ) about 7,500 years ago, the Mount Meager massif ( Bridge River Vent ) about 2,350 years ago, and Mount St. Helens in 1980. Major cities affected by a disturbance in this subduction zone include Vancouver and Victoria , British Columbia; Seattle , Washington; and Portland , Oregon. There are no contemporaneous written records of

3978-849: The North American Plate along the west coast of the continent from Vancouver Island to what is now Alaska. Rocks from this and the remnants of the Bonanza Island Arc which overlays Wrangellia are exposed along Alberni Inlet. Today, the inlet lies near where the Juan de Fuca Plate , Explorer Plate , and North American Plate meet along the Cascadia subduction zone . Tsunami A tsunami ( /( t ) s uː ˈ n ɑː m i , ( t ) s ʊ ˈ -/ (t)soo- NAH -mee, (t)suu- ; from Japanese : 津波 , lit.   'harbour wave', pronounced [tsɯnami] )

4080-637: The Puget Sound region was the magnitude 6.8 2001 Nisqually earthquake . Intraslab earthquakes in Cascadia occur in areas where the subducting plate has high curvature . Much of the seismicity that occurs off the coast of northern California is due to intraplate deformation within the Gorda plate . Similar to the distribution of interplate earthquakes in Cascadia, intraslab earthquakes are infrequent in Oregon, with its strongest earthquake since statehood being

4182-497: The Seattle Fault around 900–930 CE that generated 3 meters of uplift and a 4-5 meter tsunami. A substantial number of forearc interplate earthquakes also occur in northern California. Much less interplate seismicity occurs in Oregon compared to Washington and northern California, although Oregon hosts more volcanic activity than its neighboring states. Intraslab earthquakes, frequently associated with stresses within

Alberni Inlet - Misplaced Pages Continue

4284-530: The gravitational pull of the Moon and the Sun , a tsunami is generated by the displacement of water from a large event. Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer. Rather than appearing as a breaking wave , a tsunami may instead initially resemble a rapidly rising tide . For this reason, it is often referred to as a tidal wave , although this usage

4386-487: The western red cedar and comparing them to the living specimens meters away from the banks, they were able to approximate their year of death. There were rings up until the year 1699, indicating that the incident had occurred shortly thereafter. Root samples confirmed their conclusion, narrowing the time frame to the winter of 1699 to 1700. As with the arrowgrass site, the banks of the Copalis River are lined with

4488-427: The "t," since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is /ts/ . The term has become commonly accepted in English, although its literal Japanese meaning is not necessarily descriptive of the waves, which do not occur only in harbours. Tsunamis are sometimes referred to as tidal waves . This once-popular term derives from the most common appearance of

4590-570: The 1990s. In the 1980s, geophysicists Tom Heaton and Hiroo Kanamori of Caltech compared the generally quiet Cascadia to more active subduction zones elsewhere in the Ring of Fire . They found similarities to faults in Chile, Alaska, and Japan's Nankai Trough , locations known for megathrust earthquakes , a conclusion that was met with skepticism from other geophysicists at the time. A 1996 study published by seismologist Kenji Satake supplemented

4692-426: The 5.6 magnitude 1993 Scotts Mills earthquake , an oblique-slip quake. Megathrust earthquakes are the most powerful earthquakes known to occur, and can exceed magnitude 9.0, which releases 1,000 times more energy than magnitude 7.0 and 1 million times more energy than a magnitude 5.0. They occur when enough energy (stress) has accumulated in the "locked" zone of the fault to cause a rupture. The magnitude of

4794-551: The Cascadia subduction zone is anticipated to be capable of causing widespread destruction throughout the Pacific Northwest . Prior to the 1980s, scientists thought that the subduction zone did not generate earthquakes like other subduction zones around the world, but research by Brian Atwater and Kenji Satake tied together evidence of a large tsunami on the Washington coast with documentation of an orphan tsunami in Japan (a tsunami without an associated earthquake). The two pieces of

4896-818: The Great Lakes, the Aegean Sea, the English Channel, and the Balearic Islands, where they are common enough to have a local name, rissaga . In Sicily they are called marubbio and in Nagasaki Bay, they are called abiki . Some examples of destructive meteotsunamis include 31 March 1979 at Nagasaki and 15 June 2006 at Menorca, the latter causing damage in the tens of millions of euros. Meteotsunamis should not be confused with storm surges , which are local increases in sea level associated with

4998-601: The Hyndman and Wang diagram (not shown, click on reference link below) the "locked" zone is storing up energy for an earthquake, and the "transition" zone, although somewhat plastic, could probably rupture. The Cascadia subduction zone runs from triple junctions at its north and south ends. To the north, just below Haida Gwaii , it intersects the Queen Charlotte Fault and the Explorer Ridge . To

5100-405: The Juan de Fuca and North America plates. New Juan de Fuca plate is created offshore along the Juan de Fuca Ridge . The Juan de Fuca plate moves toward, and eventually is pushed under the continent (North American plate). The zone separates the Juan de Fuca plate , Explorer plate , Gorda plate , and North American plate . Here, the oceanic crust of the Pacific Ocean has been sinking beneath

5202-556: The M t scale match as closely as possible with the moment magnitude scale. Cascadia subduction zone 45°N 124°W  /  45°N 124°W  / 45; -124 The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary , about 100–200 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in

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5304-528: The Pacific Northwest region is not well prepared for such a colossal earthquake. The earthquake is expected to be similar to the 2011 Tōhoku earthquake and tsunami , because the rupture is expected to be as long as the 2004 Indian Ocean earthquake and tsunami . The resulting tsunami might reach heights of approximately 30 meters (100 ft). FEMA estimates some 13,000 fatalities from such an event, with another 27,000 injured, which would make it

5406-422: The Pacific Ocean on the west coast of the island. The inlet is narrow for its entire length, generally reaching a width of 1 to 2 km (0.6 to 1 mi). Shallow areas separate the waters into two basins, one near the entrance from Barkley Sound reaching a depth of 40 m (130 ft) and another near Sproat Narrows that is 37 m (121 ft) deep. The outer basin is the larger of the two. The outer bar

5508-485: The Pacific coasts of the United States and Mexico lie adjacent to each other, but the United States has recorded ten tsunamis in the region since 1788, while Mexico has recorded twenty-five since 1732. Similarly, Japan has had more than a hundred tsunamis in recorded history, while the neighbouring island of Taiwan has registered only two, in 1781 and 1867. All waves have a positive and negative peak; that is,

5610-597: The Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause. The oldest human record of a tsunami dates back to 479 BC , in the Greek colony of Potidaea , thought to be triggered by an earthquake. The tsunami may have saved the colony from an invasion by the Achaemenid Empire . The cause, in my opinion, of this phenomenon must be sought in

5712-466: The United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer , Juan de Fuca , and Gorda plates move to

5814-450: The air over and one underwater within the shallow waters of the 50-metre (164 ft) deep lagoon at Bikini Atoll . The bombs detonated about 6 km (3.7 mi; 3.2 nmi) from the nearest island, where the waves were no higher than 3 to 4 m (9.8 to 13.1 ft) when they reached the shoreline. Other underwater tests, mainly Operation Hardtack I /Wahoo in deep water and Operation Hardtack I/Umbrella in shallow water, confirmed

5916-585: The coast had fallen due to a violent earthquake and been covered by sand from the subsequent tsunami. A further ghost forest was identified by Gordon Jacoby, a dendrochronologist from Columbia University, 60 feet (18 m) underwater in Lake Washington . Unlike the other trees, these suffered from a landslide rather than a dip in the fault during a separate event around 900 CE. In the 1960s, underground fractures were uncovered by oil companies in Puget Sound . These were believed to be inactive through

6018-434: The continent for about 200 million years, and currently does so at a rate of approximately 40 mm/ yr . At depths shallower than 30 km (19 mi) or so, the Cascadia zone is locked by friction while stress slowly builds up as the subduction forces act, until the fault's frictional strength is exceeded and the rocks slip past each other along the fault in a megathrust earthquake . Below 30 km (19 mi)

6120-413: The danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed. A typical wave period for a damaging tsunami is about twelve minutes. Thus, the sea recedes in the drawback phase, with areas well below sea level exposed after three minutes. For the next six minutes, the wave trough builds into a ridge which may flood the coast, and destruction ensues. During

6222-464: The deadliest natural disaster in American, and North American, history. FEMA further predicts that a million people will be displaced, with yet another 2.5 million requiring food and water. An estimated 1/3 of public safety workers will not respond to the disaster due to a collapse in infrastructure and a desire to ensure the safety of themselves and their loved ones. Other analyses predict that even

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6324-455: The deep ocean has a much larger wavelength of up to 200 kilometres (120 mi). Such a wave travels at well over 800 kilometres per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft). This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage. The velocity of

6426-494: The earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska. Examples of tsunamis originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks in 1929, and Papua New Guinea in 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into

6528-408: 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. The Roman historian Ammianus Marcellinus ( Res Gestae 26.10.15–19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of

6630-472: The east and slide below the much larger mostly continental North American plate . The zone varies in width and lies offshore beginning near Cape Mendocino , Northern California, passing through Oregon and Washington , and terminating at about Vancouver Island in British Columbia . The Explorer, Juan de Fuca, and Gorda plates are some of the remnants of the vast ancient Farallon plate which

6732-406: The flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are. Other than by landslides or sector collapse , volcanoes may be able to generate waves by pyroclastic flow submergence, caldera collapse, or underwater explosions. Tsunamis have been triggered by a number of volcanic eruptions, including

6834-494: The gravitational pull of the moon and sun rather than the displacement of water. Although the meanings of "tidal" include "resembling" or "having the form or character of" tides, use of the term tidal wave is discouraged by geologists and oceanographers. A 1969 episode of the TV crime show Hawaii Five-O entitled "Forty Feet High and It Kills!" used the terms "tsunami" and "tidal wave" interchangeably. The term seismic sea wave

6936-409: The harbour at Halifax , Nova Scotia , Canada . There have been studies of the potential for the use of explosives to induce tsunamis as a tectonic weapon . As early as World War II (1939–1945), consideration of the use of conventional explosives was explored, and New Zealand's military forces initiated Project Seal , which attempted to create small tsunamis with explosives in the area of what

7038-437: The incident had taken place around midnight of 27–28 January 1700, ten hours after the earthquake occurred. The original magnitude 9.0 earthquake in the Pacific Northwest had thus occurred around 9 pm Pacific Standard Time on 26 January 1700. The Cascadia subduction zone is a 1,000 km (620 mi) long dipping fault that stretches from Northern Vancouver Island to Cape Mendocino in northern California. It separates

7140-557: The intensity of tsunamis were the Sieberg - Ambraseys scale (1962), used in the Mediterranean Sea and the Imamura-Iida intensity scale (1963), used in the Pacific Ocean. The latter scale was modified by Soloviev (1972), who calculated the tsunami intensity " I " according to the formula: where H a v {\displaystyle {\mathit {H}}_{av}} is the "tsunami height" in metres, averaged along

7242-562: The intensively studied tsunamis in 2004 and 2011, a new 12-point scale was proposed, the Integrated Tsunami Intensity Scale (ITIS-2012), intended to match as closely as possible to the modified ESI2007 and EMS earthquake intensity scales. The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on

7344-441: The last 3,500 years, suggesting a return time of about 500 years. Seafloor core evidence indicates that there have been forty-one subduction zone earthquakes on the Cascadia subduction zone in the past 10,000 years, suggesting a general average earthquake recurrence interval of only 243 years. Of these 41, nineteen have produced a "full margin rupture", wherein the entire fault opens up. By comparison, similar subduction zones in

7446-777: The length of the inlet. The inlet splits the Pelham Range . Alberti Inlet is a fjord cut by an outlet glacier draining from Pleistocene -age ice caps in the mountainous interior of Vancouver Island and later flooded during the sea level rise at the end of the Last Glacial Maximum . The surrounding land is composed of Wrangellia Terrane , constituting the remnants of a island volcanic arc that started forming approximately 300 million years ago and seafloor flood basalts from about 230 million years ago. Periods of dormancy created layers of sediment embedded between lava flows. After these events, Wrangellia accreted to

7548-483: The low barometric pressure of passing tropical cyclones, nor should they be confused with setup, the temporary local raising of sea level caused by strong on-shore winds. Storm surges and setup are also dangerous causes of coastal flooding in severe weather but their dynamics are completely unrelated to tsunami waves. They are unable to propagate beyond their sources, as waves do. The accidental Halifax Explosion in 1917 triggered an 18-metre (59 ft) high tsunami in

7650-636: The nearest coastline, with the tsunami height defined as the rise of the water level above the normal tidal level at the time of occurrence of the tsunami. This scale, known as the Soloviev-Imamura tsunami intensity scale , is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami. This formula yields: In 2013, following

7752-405: The next six minutes, the wave changes from a ridge to a trough, and the flood waters recede in a second drawback. Victims and debris may be swept into the ocean. The process repeats with succeeding waves. As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events. The first scales used routinely to measure

7854-804: The ocean and generate a tsunami. They dissipated before travelling transoceanic distances. 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 1960 Valdivia earthquake ( M w 9.5), 1964 Alaska earthquake ( M w 9.2), 2004 Indian Ocean earthquake ( M w 9.2), and 2011 Tōhoku earthquake ( M w 9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis ) that can cross entire oceans. Smaller ( M w 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only

7956-437: The ocean, meteorite impacts, and the weather when the atmospheric pressure changes very rapidly—can generate such waves by displacing water. The use of the term tsunami for waves created by landslides entering bodies of water has become internationally widespread in both scientific and popular literature, although such waves are distinct in origin from large waves generated by earthquakes. This distinction sometimes leads to

8058-529: The past 3,000 years or so. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. The 1906 San Francisco earthquake seems to have been a major exception to this correlation, however, as it was not preceded by a major Cascadia quake. The last known great earthquake in the northwest was the 1700 Cascadia earthquake , 324 years ago. Geological evidence indicates that great earthquakes (> magnitude 8.0) may have occurred sporadically at least seven times in

8160-414: The plate interface exhibits episodic tremor and slip . The width of the Cascadia subduction zone varies along its length, depending on the angle of the subducted oceanic plate, which heats up as it is pushed deeper beneath the continent. As the edge of the plate sinks and becomes hotter and more molten, the subducting rock eventually loses the ability to store mechanical stress; earthquakes may result. On

8262-482: The possibility of a meteorite causing a tsunami is debated. Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. 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. More specifically,

8364-433: The potential energy. Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale M t {\displaystyle {\mathit {M}}_{t}} , calculated from, where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicentre, a , b and D are constants used to make

8466-458: The puzzle were linked, and they then realized that the subduction zone was more hazardous than previously suggested. In 2009, some geologists predicted a 10% to 14% probability that the Cascadia subduction zone will produce an event of magnitude 9.0 or higher in the next 50 years. In 2010, studies suggested that the risk could be as high as 37% for earthquakes of magnitude 8.0 or higher. Geologists and civil engineers have broadly determined that

8568-414: The region 60 kilometers (about 40 miles) downdip (east) of the deformation front (where plate deformation begins) is fully locked (the plates do not move past each other). Further downdip, there is a transition from fully locked to aseismic sliding . In 1999, a group of Continuous Global Positioning System sites registered a brief reversal of motion of approximately 2 centimeters (0.8 inches) over

8670-520: The research by Atwater et al. with tsunami evidence across the Pacific. Japanese annals, which have recorded natural disasters since approximately 600 CE, had reports of a sixteen-foot tsunami that struck the coast of Honshu Island during the Genroku . Since no earthquake had been observed to produce it, scholars dubbed it an " orphan tsunami ". Translating the Japanese calendar , Satake found

8772-505: The researchers to come up with an estimated date range for the event; the midpoint was in the year 1701. During low tide one day in March 1986, paleogeologist Brian Atwater dug along Neah Bay with a nejiri gama , a small hand hoe. Under a top layer of sand, he uncovered a distinct plant— arrowgrass —that had grown in a layer of marsh soil. This finding was evidence that the ground had suddenly sunk under sea level, causing saltwater to kill

8874-605: The results. Analysis of the effects of shallow and deep underwater explosions indicate that the energy of the explosions does not easily generate the kind of deep, all-ocean waveforms typical of tsunamis because most of the energy creates steam , causes vertical fountains above the water, and creates compressional waveforms. Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions. Tsunamis are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and bolides . They cause damage by two mechanisms:

8976-426: The sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria . The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually caused by earthquakes, but can also be attributed to landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. However,

9078-400: The smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it, even with waves that do not appear to be large. While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in

9180-652: The south, just off Cape Mendocino in California, it intersects the San Andreas Fault and the Mendocino Fracture Zone at the Mendocino triple junction . Subduction zones experience various types of earthquakes (or seismicity); including slow earthquakes , megathrust earthquakes , interplate earthquakes , and intraplate earthquakes . Unlike other subduction zones on Earth, Cascadia currently experiences low levels of seismicity and has not generated

9282-520: The subducting plate in convergent margins , occur most frequently in northern Cascadia along the west coast of Vancouver Island and in Puget Sound, and in southern Cascadia within the subducting Gorda plate , near the Mendocino triple junction offshore of northern California. The 1949 Olympia earthquake was a damaging magnitude 6.7 intraslab earthquake that occurred at 52 km depth and caused eight deaths. Another notable intraslab earthquake in

9384-468: The subduction interface than the locked area where megathrust earthquakes occur. The depth of tremor along the subduction interface in Cascadia ranges from 28 km to 45 km, and the motion is so slow that it is not felt at the surface by people or animals, but it can be measured geodetically . The highest density of tremor activity in Cascadia occurs from northern Washington into southern Vancouver Island, and in northern California. Tremor in Cascadia

9486-457: The transoceanic reach of significant seismic tsunamis, and 2) that the force that displaces the water is sustained over some length of time such that meteotsunamis cannot be modelled as having been caused instantaneously. In spite of their lower energies, on shorelines where they can be amplified by resonance, they are sometimes powerful enough to cause localised damage and potential for loss of life. They have been documented in many places, including

9588-447: The understanding of the other source mechanisms. Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths. These are comparable to seismic tsunamis, but usually with lower energies. Essentially, they are dynamically equivalent to seismic tsunamis, the only differences being 1) that meteotsunamis lack

9690-457: The use of other terms for landslide-generated waves, including landslide-triggered tsunami , displacement wave , non-seismic wave , impact wave , and, simply, giant wave . While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. The Sumatran region

9792-475: The vegetation. The event had happened so quickly that the top layer of sand sealed away the air, thus preserving centuries-old plants. In 1987, Atwater mounted another expedition paddling up the Copalis River with Dr. David Yamaguchi, who was then studying the eruptions of Mount St. Helens . The pair happened upon a section of " ghost forest ", so-called due to the dead, gray stumps left standing after

9894-399: The very largest tsunamis, the approaching wave does not break , but rather appears like a fast-moving tidal bore . Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front. When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up . Run up is measured in metres above

9996-439: The west coast of Vancouver Island, such as Tofino and Ucluelet , are at risk for a sudden, earthquake initiated, 1–2 m subsidence. Studies of past earthquake traces on both the northern San Andreas Fault and the southern Cascadia subduction zone indicate a correlation in time which may be evidence that quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas during at least

10098-455: The world usually have such earthquakes every 100 to 200 years; the longer interval here may indicate unusually large stress buildup and subsequent unusually large earthquake slip. There is also evidence of accompanying tsunamis with every earthquake. One strong line of evidence for these earthquakes is convergent timings for fossil damage from tsunamis in the Pacific Northwest and historical Japanese records of tsunamis. The next rupture of

10200-576: Was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean . The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes , but the understanding of tsunamis remained slim until the 20th century, and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do. This ongoing research

10302-521: Was confirmed in 1958, when a giant landslide in Lituya Bay , Alaska, caused the highest wave ever recorded, which had a height of 524 metres (1,719 ft). The wave did not travel far as it struck land almost immediately. The wave struck three boats—each with two people aboard—anchored in the bay. One boat rode out the wave, but the wave sank the other two, killing both people aboard one of them. Another landslide-tsunami event occurred in 1963 when

10404-496: Was the second wave that caused most of the damage, lifting houses off their foundations and sweeping log booms onto the shore. The second wave was followed by four more waves ranging in height from 1.5 to 1.8 metres (5–6 ft) and occurring at roughly 90-minute intervals. In total, the tsunami washed away 55 homes and damaged 375 others. Tsunamis repeatedly hit the First Nations village Huu-ay-aht of Sarita , which

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