Tsunami & Floods

.

.

Description or Situation

.

.

.

Overview

.

Tsunami's, tidal waves and flood waters resulting from such events have historically changed land configurations as well as cultures residing upon those regions for many centuries. These are situations which are predominantly known to impact coastal regions and do not typically present concerns for people living away from these areas. Many victims of such events are not always limited to being natives of these impacted regions. Some were simply visiting when the situation occurred. In addition, ... many coastal regions susceptible to tsunamis, tidal waves and extreme flooding have a degree of industry located close enough to incur substantial or catastrophic damage which in turn can effect populations and cultures around the world. Though these events do not occur regularly enough to prompt fear they have been known to impact regions as far inland as 600 miles which should draw a degree of curiosity at the very least. Reports in history have recorded tidal waves as high as a third of a mile high while more ancient accounts claim waves reaching a full mile according to some cultural legends. These are events that most certainly prompt concern as the earth continues to change in it's cyclic life. Flooding has similar long term effects and consequences which can be caused by overwhelming tidal conditions as well as heavy amounts of precipitation and failure of retention systems commonly known as levee's and dams. Either way, ... all these events have the potential to destroy human life and habitation.

.

.

The following is intended to aid those seeking information related to potential disasters and calamities associated with tsunami's and floods.

.

.

.

What is a Tsunami, tidal wave or flood?

.

Tsunamis & Tidal Waves

Common use of the word tidal wave refers to a gigantic and enormously destructive wave caused by an underwater earthquake or volcanic eruption—what scientists would properly call a tsunami. When scientists use the word tidal wave, they normally are referring to an unusually large wave or bulge of water that sometimes occurs around a high tide. These tidal waves are certainly big and powerful, but they are tiny in comparison with tsunamis.

A tsunami, also known as a seismic sea wave, 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. Other definitions simply describe a tsunami and tidal wave as an unusually high or large and unscheduled wall or volume of ocean water.

.

Floods

A flood is an overflow of water that submerges land which is usually dry. The European Union (EU) Floods Directive defines a flood as a covering by water of land not normally covered by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide.

.

Principal types

Areal,  Riverine (Channel),  Estuarine and coastal,  Urban flooding,  Catastrophic. 

For detailed descriptions of these types of floods go to the source.

[Source]

.

.

.

What are the causes?

.

Tsunamis & tidal waves

The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravity. Tides do not play any part in the generation of tsunamis.

.

Seismicity

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, 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 a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events.

Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long, whereas normal ocean waves have a wavelength of only 30 or 40 meters), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimeters (12 in) above the normal sea surface. 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, 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 Hawaii with a 14-metre high (46 ft) surge. The area where the earthquake occurred is where the Pacific Ocean floor is sub-ducting (or being pushed downwards) under Alaska.

Examples of tsunami originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilized sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before traveling 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 , 1964 Alaska earthquake , 2004 Indian Ocean earthquake , and 2011 Tōhoku earthquake , are recent examples of powerful mega-thrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller, earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can only devastate nearby coasts, but can do so in only a few minutes.

.

Landslides

In the 1950s, 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 in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 meters (over 1700 feet). The wave did not travel far, as it struck land almost immediately. Two people fishing in the bay were killed, but another boat amazingly managed to ride the wave.

Another landslide-tsunami event occurred in 1963 when a massive landslide from Monte Toc entered the Vajont Dam in Italy. The resulting wave surged over the 262 m (860 ft) high dam by 250 meters (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 in 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 water. This has been shown to lead to effect water in enclosed bays and lakes, but a landslide large enough to cause 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 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.

.

Meteotsunamis

Some meteorological conditions, especially deep depressions such as tropical cyclones, can generate a type of storm surge called a meteotsunami which raises water heights above normal levels, often suddenly at the shoreline.

In the case of deep tropical cyclones, this is due to very low atmospheric pressure and inward swirling winds causing an uplifted dome of water to form under and travel in tandem with the storm. When these water domes reach shore, they surge upward in shallows and laterally much as do earthquake-generated tsunamis, typically arriving shortly after landfall of the storm's eye.

.

Man-made or triggered tsunamis

[See also: Tsunami bomb]

There have been studies of the potential of induction of and at least one actual attempt to create tsunami waves as a tectonic weapon. In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park, ... the attempt failed. There has been considerable speculation on the possibility of using nuclear weapons to cause tsunamis near to an enemy coastline. Even during World War II consideration of the idea using conventional explosives was explored. Nuclear testing in the Pacific Proving Ground by the United States seemed to generate poor results. Operation Crossroads fired two 20 kilotons of TNT (84 TJ) bombs, one in the air and one underwater, above and below the shallow (50 m (160 ft)) waters of the Bikini Atoll lagoon. Fired about 6 km (3.7 mi) from the nearest island, the waves there were no higher than 3–4 m (9.8–13.1 ft) upon reaching the shoreline. Other underwater tests, mainly Hardtack I/Wahoo (deep water) and Hardtack I/Umbrella (shallow water) confirmed the results. Analysis of the effects of shallow and deep underwater explosions indicate that the energy of the explosions doesn't easily generate the kind of deep, all-ocean wave forms which are tsunamis; most of the energy creates steam, causes vertical fountains above the water, and creates compressional wave forms. Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which don't occur in explosions.

[Source]

.

Megatsunami

A megatsunami is a term used for a very large wave created by a large, sudden displacement of material into a body of water.

Megatsunamis have quite different features from other, more usual type of tsunamis. Most tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquake and rise or fall in the sea floor, causing water to be displaced. Ordinary tsunamis have shallow waves out at sea, and the water piles up to a wave height of up to about 10 meters (33 feet) as the sea floor becomes shallow near land. By contrast, megatsunamis can occur in locations where there is a very large amount of material that suddenly falls into water, or anywhere in water (for meteor impact), or may be caused by volcanic activity, and can have extremely high initial wave heights of hundreds and possibly thousands of meters, far beyond any ordinary tsunami, as the water is "splashed" upwards and outwards by the impact or displacement. As a result, two heights are sometimes quoted for megatsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.

Modern megatsunamis include the one associated with the 1883 eruption of Krakatoa (volcanic eruption), the 1958 Lituya Bay megatsunami (landslide into a bay), and the wave resulting from the Vajont Dam landslide (caused by human activity destabilizing sides of valley). Prehistoric examples include the Storegga Slide (landslide), and the Chicxulub, Chesapeake Bay and Eltanin meteor impacts. 

[Source]

.

Floods

Flooding may occur as an overflow of water from water bodies, such as a river or lake, in which the water over tops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals.

Floods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry.

Some floods develop slowly, while others such as flash floods, can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighborhood or community, or very large, affecting entire river basins. 

[Source]

.

.

.

What are the effects?

.

Tsunamis & tidal waves

All waves have a positive and negative peak, i.e. 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 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. Drawback can exceed hundreds of meters, and people unaware of 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 12 minutes. This means that if the drawback phase is the first part of the wave to arrive, the sea will recede, with areas well below sea level exposed after 3 minutes. During the next 6 minutes the tsunami wave trough builds into a ridge, and during this time the sea is filled in and destruction occurs on land. During the next 6 minutes, the tsunami wave changes from a ridge to a trough, causing flood waters to drain and drawback to occur again. This may sweep victims and debris some distance from land. The process repeats as the next wave arrives.

.

Mega Tsunami: Wave of Destruction

Over the last fifty years scientists have found in nature enough evidence of a previously unknown natural phenomenon that, although similar to "traditional" Tsunamis, may in fact cause an incomparable level of destruction along the coastlines. Such wave of huge proportions will be probably triggered in the Atlantic Ocean anytime in the next 500 years thus posing a daunting threat for the East Coast of America, North Africa and Europe. 

[Source]

.

Megatsunami threats

Volcanic islands (such as Reunion and the Hawaiian Islands) can cause megatsunamis to hit other nearby islands in the same chain because often they are structurally little more than large, unstable piles of loosely aggregated material heaped up by successive eruptions. Evidence for large landslides has been found in the form of extensive underwater debris aprons around them composed of the material which has slipped into the ocean. In recent years five such debris aprons have been found in the Hawaiian Islands alone.

Some geologists speculate that the most likely candidate for the source of the next large-scale megatsunami is the island of La Palma, in the Canary Islands, although further research has dismissed the threat. During the 1949 eruption the western half of the Cumbre Vieja ridge slipped several meters downwards into the Atlantic Ocean. It is believed that this process was driven by the pressure caused by the rising magma heating and vaporizing water trapped within the structure of the island, causing the island's structure to be pushed apart. During an eruption that is anticipated to occur sometime within the next few thousand years the western half of the island, weighing perhaps 500 billion tonnes, may catastrophically slide into the ocean in a single event. Were this to happen it could in theory generate a megatsunami, causing local wave heights of hundreds of meters and a likely height of around 10–25 m at the Caribbean and the Eastern American seaboard coast several hours later.

Besides fjords in Alaska, many locations face threats of localized, but still potentially dangerous, mega-tsunami-type waves. Some geologists speculate that an unstable rock face at the north end of Harrison Lake in the Fraser Valley in southwestern British Columbia could collapse into the lake, generating a large wave that might destroy the town and Harrison Hot Springs resort at the south end.

[Source]

.

Floods

Primary effects

The primary effects of flooding include loss of life, damage to buildings and other structures, including bridges, sewerage systems, roadways, and canals.

Floods also frequently damage power transmission and sometimes power generation, which then has knock-on effects caused by the loss of power. This includes loss of drinking water treatment and water supply, which may result in loss of drinking water or severe water contamination. It may also cause the loss of sewage disposal facilities. Lack of clean water combined with human sewage in the flood waters raises the risk of waterborne diseases, which can include typhoid, giardia, cryptosporidium, cholera and many other diseases depending upon the location of the flood. Damage to roads and transport infrastructure may make it difficult to mobilize aid to those affected or to provide emergency health treatment. Flood waters typically inundate farm land, making the land unworkable and preventing crops from being planted or harvested, which can lead to shortages of food both for humans and farm animals. Entire harvests for a country can be lost in extreme flood circumstances. Some tree species may not survive prolonged flooding of their root systems.

.

Secondary and long-term effects

Economic hardship due to a temporary decline in tourism, rebuilding costs, or food shortages leading to price increases is a common after-effect of severe flooding. The impact on those affected may cause psychological damage to those affected, in particular where deaths, serious injuries and loss of property occur.

Urban flooding can lead to chronically wet houses, which are linked to an increase in respiratory problems and other illnesses. Urban flooding also has significant economic implications for affected neighborhoods. In the United States, industry experts estimate that wet basements can lower property values by 10-25 percent and are cited among the top reasons for not purchasing a home. According to the U.S. Federal Emergency Management Agency (FEMA), almost 40 percent of small businesses never reopen their doors following a flooding disaster. In the United States, insurance is available against flood damage to both homes and businesses.

[Source]

.

 .

.

Events in history

.

List of historical tsunamis

World's Tallest Tsunami

List of deadliest floods - Wikipedia, the free encyclopedia

.

.

.

Videos

.

Tsunamis 101

Tsunami - Caught On Camera

Mega Tsunamis

.

.

.

Find "Solutions to tsunami & floods"

.

.

.

References

.

https://en.wikipedia.org/wiki/Flood

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

https://en.wikipedia.org/wiki/Megatsunami

http://www.apocalypse-soon.com/megatsunami.htm

https://en.wikipedia.org/wiki/List_of_historical_tsunamis

http://video.nationalgeographic.com/video/101-videos/tsunami-101

http://www.history.com/shows/how-the-earth-was-made/videos/mega-tsunamis

http://www.sms-tsunami-warning.com/pages/mega-tsunami-wave-of-destruction#.VpxCxlJUXNM

P2S