Tsunami Information Center(TIC)

Storms, storm surges, tsunamis, swell, seiche, sea level rise, freak waves, tidal motion may have extreme characteristics sometimes. Those should be investigated, monitored, modeled, observed, forecasted and necessary precautions can be developed for reduction of risk and safety of coastal communities.

A disaster is a sudden, calamitous event that seriously disrupts the functioning of a community or society and causes human, material, and economic or environmental losses that exceed the community’s or society’s ability to cope using its own resources. A disaster occurs when a hazard impacts on vulnerable people. The combination of hazards, vulnerability and inability to reduce the potential negative consequences of risk results in disaster. Disaster Management can be defined as the organization and management of resources and responsibilities for dealing with all humanitarian aspects of emergencies, in particular preparedness, response and recovery in order to lessen the impact of disasters. The first people to respond to a disaster are those living in the local community. They are the first to start rescue and relief operations. The Red Cross and Red Crescent National Societies therefore focus on community-based disaster preparedness, which assists communities to reduce their vulnerability to disasters and strengthen their capacities to resist them. When the capacity of a community or country to respond and recover from a disaster is overwhelmed, and upon request from the National Society, the International Federation uses its regional and international networks, assets and resources to bring assistance to the communities and National Red Cross Red Crescent Society which is assisting them. At an international level the International Federation advocates with Governments, international organisations and humanitarian donors for better practice and accountability in disaster management and greater respect of the dignity of the vulnerable people.

The United Nations Office of Disaster Risk Reduction UNISDR develop basic definitions on disaster risk reduction to promote a common understanding on the subject for use by the public, authorities and practitioners. The terms are based on a broad consideration of different international sources. The terminology is available at; https://www.unisdr.org/we/inform/terminology

1) How Oceans Behave Oceans cover about 70% of the Earth's surface. The oceans contain roughly 97% of the Earth's water supply. The ocean appears blue because it is reflecting the blue colour of the sky.

The oceans of Earth serve many functions, especially affecting the weather and temperature. They moderate the Earth's temperature by absorbing incoming solar radiation (stored as heat energy). Moving ocean currents distribute this heat energy around the globe. This heats the land and air during winter and cools it during summer. The Earth's oceans are all connected to one another. Until the year 2000, there were four recognized oceans: The Pacific, Atlantic, Indian, and Arctic. In the spring of 2000, the International Hydrographic Organization delimited a new ocean, the Southern Ocean (it surrounds Antarctica and extends to 60 degrees latitude).

2) Wave Behaviour in Shallow Water Waves moving out away from a storm eventually organize themselves into a swell, and eventually, if they are not destroyed by interference, they reach the shore. The seafloor shallows as the waves approach shore, and eventually the waves touch bottom (they reach wave base). At this point we shift from "deep water" to "shallow water" (from the wave's perspective).

The waves begin to slow down (celerity decreases) due to friction and wave celerity now depends on water depth. So as the waves come to shore from the sea,

•  they change from deep-water waves to shallow water waves at wave base, where water depth = 1/2 wavelength,
• wavelength decreases, period stays the same
•  height increases
• wave breaks and becomes
• swash, then backwash

Wave Transformation As the waves move from deep toward shallow water they are transformed by the variation in the bottom configuration and the existence of obstacle such as islands and breakwater. As a result, the height, length, celerity, and direction of waves may change. Finally, waves become unstable and break at a certain water depth. Wave Refraction Imagine that a single wave train is coming towards shore. If the sea floor were a perfect incline, the wave would reach wave base at the same distance offshore. The wave would steepen at the same place offshore, and break at the same place at the shore. But in many places, the seafloor is not perfect incline. Even though it is under water, it has hills and valleys as you walk along, parallel to the shore. When the area just offshore of the beach has topography, waves reach wave base farther offshore. At this point, orbits change to ellipses, and the wave slows down. The part of the wave that hasn't touched bottom yet continues to move toward the beach, now moving faster than the part of the wave that has slowed down. This bending of waves around objects is called wave refraction. Wave refraction causes waves to strike as near to parallel to shore as they can.

Wave Diffraction Diffraction usually happens when waves encounter surface-piercing obstacle, such as a breakwater or an island. It would seem that on the land side of the island, the water would be perfectly calm; however, it is not. The waves, after passing the island, turn into the region behind the island and carry wave energy and the wave crest into this so-called 'shadow zone.' The turning of the waves into the sheltered region is due to the changes in wave height (say along the crest) in the same wave. Wave Breaking The separation of water particles from the wave under the action of gravity is known as wave breaking. Wave breaking process causes energy dissipation by turbulence. Wave breaking is one of the most commonly observed features of water waves. Breaking is always a nonlinear phenomenon and is therefore extremely difficult to describe analytically. Types of Wave Breaking

1) Tsunami Tsunami is the Japanese word for harbor (tsu) wave (nami). Tsunami is a series of very large waves generated by an underwater disturbance: a submarine earthquake, a submarine landslide, a volcanic eruption or a meteorite. Tsunamis are very long waves. Due to their long wavelength, the distance between two crests may reach 100 km. The speed of a tsunami wave depends on ocean depth, therefore they travel faster in deep ocean and they slow in shallow waters. Tsunamis may travel very fast in deep ocean, as fast as a jet plane. Although, in deep ocean tsunami height does not exceed a few meters when they approach the coast and enter shallow waters they slow down but their height increase. The morphology of the ocean floor and of the coastline will influence the size of the wave. Tsunamis are different from wind waves, that we may observe on the beach. When tsunamis flood coastal areas they can penetrate large distances inland (more than 1 km); when the waves retreat they carry large objects, people and debris. A tsunami is not a single wave but a series of waves. Tsunamis can occur at any time, there is no tsunami season! Do you know?

• The Indian Ocean tsunami on 26 December 2004 in Indian Ocean claimed more than 230 000 lives throughout the Indian Ocean coast
• That there are natural warning signs of a possible tsunami: the earthquake itself- if you feel an earthquake near the coast you must evacuate towards higher ground; Sometimes tsunami arrival is preceded by a noticeable fall in sea level as the ocean retreats seaward exposing the seafloor.
• A tsunami occurred after the 1999 Ismit earthquake in Turkey. At Tavsancil, the sea in the local port receded first and when the sea came back it flooded the first floor of some hoses

2) Storm and Storm Surge Waves come in all shapes and sizes—from small ones calmly lapping on the shore to large rogue waves out at sea. Storms interact with the ocean on the surface, from hurricanes to tsunamis. Hurricanes, cyclones, and typhoons are all the same weather phenomenon; it is just used as different names for these storms in different places. In the Atlantic and Northeast Pacific, the term “hurricane” is used. The same type of disturbance in the Northwest Pacific is called a “typhoon” and “cyclones” occur in the South Pacific and Indian Ocean (http://oceanservice.noaa.gov/facts/cyclone.html). Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide. It’s the change in the water level that is due to the presence of the storm. Since storm surge is a difference between water levels, it does not have a reference level.

Storm surge is caused primarily by the strong winds in a hurricane or tropical storm. The low pressure of the storm has minimal contribution! In general, storm surge occurs where winds are blowing onshore. The highest surge tends to occur near the “radius of maximum winds,” or where the strongest winds of the hurricane occur. There are several factors that contribute to the amount of surge a given storm produces at a given location:

• Central Presssure (Lower pressure will produce a higher surge)
• Storm Intensity (Stronger winds will produce a higher surge)
• Size (Larger storm will produce higher surge)
• Angle of approach to coast
• Shape of the coastline
• Width and Slope of the Ocean Bottom
• Local Features

3)Seiche, Swell, Tide, Freak Waves Seiches are periodic oscillations of water level set in motion by some atmospheric disturbance passing over a Great Lake. The disturbances that cause seiches include the rapid changes in atmospheric pressure with the passage of low or high pressure weather systems, rapidly-moving weather fronts, and major shifts in the directions of strong winds. Seiches exist on the Great Lakes, other large, confined water bodies, and on partially-enclosed arms of the sea. The intervals (or periods) between seiche peaks on the Great Lakes range from minutes to more than eight hours. The term was first promoted by the Swiss hydrologist François-Alphonse Forel in 1890, who had observed the effect in Lake Geneva, Switzerland. The word originates in a Swiss French dialect word that means "to sway back and forth", which had apparently long been used in the region to describe oscillations in alpine lakes.

Swell is a wave system not raised by the local wind blowing at the time of observation, but raised at some distance away due to winds blowing there, and which has moved to the vicinity of the ship, or to waves raised nearby by winds that have since died away. Swell waves travel out of a stormy or windy area and continue on in the direction of the winds that originally formed them as sea waves. The swell may travel for thousands of miles before dying away. As the swell wave advances, its crest becomes rounded and its surface smooth. Its length increases until it is approximately from 35 to 200 or more times its height. Swell waves normally come from a direction different from the direction of the prevailing wind and sea waves at the time of observation. However, sea and swell waves may occasionally be seen coming from essentially the same direction, thus making it more difficult to distinguish the two systems, especially if the sea waves are high. Sea waves and one or more systems of swell waves are frequently present at the same time, forming "cross seas." Again, sea waves may be absent (as would occur under conditions of very light winds), but one or more systems of swell waves may still be present. Tides are the alternating rise and fall of the surface of the seas and oceans. They are due mainly to the gravitational attraction (pull) of the moon and sun on the rotating earth. Two high and two low tides occur daily and, with average weather conditions, their movements can be predicted with considerable accuracy. When the moon is new or full, the gravitational forces of the sun and moon are pulling at the same side of the earth. This occurrence creates the extra-large "spring" tides. When the moon is at first and third quarter, the gravitational forces of the sun and moon are pulling at 90 degrees from each other. This occurrence yields little net tides called neap tides.

Freak, rogue, or giant waves correspond to large-amplitude waves surprisingly appearing on the sea surface (“wave from nowhere”). Such waves can be accompanied by deep troughs (holes), which occur before and/or after the largest crest. Seafarers speak of “walls of water”, or of “holes in the sea”, or of several successive high waves (“three sisters”), which appear without warning. But since the 70s of the last century, oceanographers have started to believe them. Observations gathered by the oil and shipping industries suggest there really is something like a true monster of the deep that devours ships and sailors without mercy or warning. There are several definitions for such surprisingly huge waves. Very often the term “extreme waves” is used to specify the tail of some typical statistical distribution of wave heights (generally a Rayleigh distribution); meanwhile the term “freak waves” describes the large-amplitude waves occurring more often than would be expected from the background probability distribution.