Questions regarding the CWarn System

Where does the CWarn Tsunami Early Warning System work?
Where does the earthquake information come from and is it reliable?

Do I receive alerts for all the threat areas, or just for my registered location?
Are there any additional international costs or charges incurred?
What do I get with my membership of the CWarn Tsunami Early Warning System?
What happens to my membership after the one-year period is up?
Is there anything that this SMS Early Warning system is NOT?
What do the alert levels green, orange and red mean?

Questions regarding Tsunamis in general

What is a tsunami?
How do tsunami occur?

How do I recognise a tsunami?
Could Nuclear testing create a tsunami?

How is a tsunami wave different from a normal wave?
How does a tsunami behave as it approaches land?
How long does it take a tsunami to reach land?

How many waves are there in a tsunami?
What is run-up and inundation?

How are tsunami wave heights measured?
What is the "wrap-around" effect?
Do all oceans have tsunamis?
What should I do or not do in a tsunami warning?
If I need to evacuate, what should I bring with me?
Can the arrival time of a tsunami be accurately predicted?
I own a boat, what should I do when there is a tsunami warning?

Q Where does the CWarn Tsunami Early Warning System work?

The CWarn Tsunami Early Warning System covers most of the mobile phone networks on Earth and as long as you are in a mobile phone coverage area you should receive the alerts. Unfortunately cell phone coverage and SMS service is not a guaranteed service by the telcos and delivery of SMS cannot be guaranteed.

Back to top

Q Where does the earthquake information come from and is it reliable?

The earthquake information comes from the international government agencies responsible for monitoring, receiving and deseminating the data. A large number of technical skills and resources are deployed by the different governments in an international effort to make this information more accurate, reliable and more meaningful.

The primary source is the Global Seismographic Network (GSN) which comprises approximetely 145 stations with the purpose of measuring earthquake information. The information is transmitted in real-time using Internet and VSAT satellite connectivity which has been established for 97% of the GSN.

Together with GSN, sea level data and deep ocean sensors monitor, measure and communicate changes in water levels. These systems are linked using available data and telecommunication networks.

When certain changes are recorded additional early warning systems come into operation and the information plus the potential threats are verified. The areas effected are located and various forecasts, advisories and alerts are computed and sent.

Back to top

Q Do I receive alerts for all the threat areas, or just for my registered location?

You will only receive alerts for your particular threat area. Your threat area is determined by the location you stipulate when you register with CWarn. If you are going away to another location, update your location on the CWarn system in order to receive threats for your new location. A full address is not required, just City/Town and Country information is enough.

Back to top

Q Are there any additional international costs or charges incurred?

There is no charge or cost whatsoever for using our tsunami early warning system. Our SMS service is FREE to you wherever you are. We are a small private volunteer group and receive no funding other than donations from individuals like you. Please support our costs by making a donation, the link is on the home page.

Back to top

Q What do I get with my membership of the CWarn Tsunami Early Warning System?

With the CWarn Tsunami Early Warning System you get peace of mind that you can live or visit coastal areas knowing that you have an extra blanket of protection in the form of timeous early warning alerts to your mobile phone via SMS. Your mobile phone is now a potential life saver for you, your family and your property.

Back to top

Q What happens to my membership after the one-year period is up?

Once you have taken out membership to the CWarn Early Warning System your membership is automatically renewed on your anniversary date. You can cancel your membership at any time simply by loging into the members area.

Back to top

Q Is there anything that this SMS Early Warning system is NOT?

This SMS-based early warning system is:

  • Not meant to replace existing formal/official means of communicating alerts or critical information.
  • Not meant to become the sole means of receivng critical alert information.
  • Not meant to be a mass public communication system for national official / disaster managers

Back to top

Q What do the alert levels green, orange and red mean?

Based on the location and magnitude of the disasters and the local population and their vulnerability, disasters are classified in three classes:

  • Green: very low likelihood of humanitarian disaster
  • Orange: potential humanitarian disaster
  • Red: very high likelihood of humanitarian disaster

Information provided by the Joint Research Center of the European Commission in the context of the Global Disaster Alert and Coordination System.

Back to top

Q What is a tsunami?

Tsunami ('soo-nar-me') is a Japanese word; 'tsu' meaning harbour and 'nami' meaning wave. Tsunamis are sometimes incorrectly called tidal waves but have nothing to do with tides. Tsunamis can travel up to 950 kilometres per hour - as fast as a passenger jet! Tsunami waves move outwards, away from their source. One or more waves can be created per event. Successive peaks can be anywhere from five to ninety minutes apart. The wave train that reaches the coast can range from 30 metre high breakers to barely noticed ripples - but in the open ocean, tsunamis have relatively small heights.

A tsunami is different from normal waves on the ocean. Wind-made ocean waves cause the water to move down to about 150 metres at most. In contrast, the passage of a tsunami involves the movement of water all the way to the seafloor. This means that the speed of a tsunami is controlled by water depth - as the wave approaches land it reaches increasingly shallow water and slows down. Compared to the front of the wave, the rear is still in slightly deeper water (so it is going slightly faster) and catches up. The result is that the wave quickly 'bunches up' and becomes much higher. The highest tsunami occur if they encounter a long and gradual shallowing of the water, because this allows enough time for the wave to interact with its surroundings and cause extensive damage to low-lying areas.

Back to top

Q How do tsunami occur?

Tsunami are actually waves caused by sudden movement of the ocean due to earthquakes, landslides on the sea floor, land slumping into the ocean, major volcanic eruptions or large meteorite impacts.

Most tsunami are caused by large earthquakes at the seafloor, when large slabs of rock are forced to move past each other suddenly causing the overlying water to move. The resulting wave moves outwards and away from this event.

Underwater landslides can cause tsunami, and so can land which slumps into the ocean. Landslides happen when slopes become too steep to withstand gravity.

Less common are tsunami initiated by volcanic eruptions. These occur in several ways:

  • if an underwater volcano erupts, the hot lava may heat the surrounding water quickly and explosively.
  • massive flows of volcanic debris such as ash can travel down the side of a volcano and into the ocean, pushing water outwards.
  • the top of an underwater volcano may collapse downwards, so that the overlying water also drops.

Large meteorite impacts that occur at sea can also trigger tsunami.

Back to top

Q How do I recognise a tsunami?

It is almost impossible to recognise an approaching tsunami. Tsunamis arrive completely unexpectedly causing huge damage in their path. Briefly before a tsunami, the sea retreats revealing the sea bottom. If you see this happen it is usually already too late. A tsunami is on its way and will arrive within seconds.

Back to top

Q Could Nuclear testing create a tsunami?

Nuclear testing at and near Pacific islands, with ample wave detection equipment included, showed that such explosions do not propagate hazardous tsunami waves.

Back to top

Q How is a tsunami wave different from a normal wave?

The waves you see at the beach are generated by wind blowing over the sea surface.  The size of these waves depends on the strength of the wind creating them and the distance over which it blows.  Generally the distance between these waves, known as the wavelength, ranges from under a metre (a couple of feet) to perhaps 300 metres (1,000 ft.).   The speed of these waves as they travel across the ocean ranges from a few kilometres an hour up to 100 kilometres an hour (60 miles an hour) in some instances.
Tsunami waves resulting from physical mechanisms behave much differently than wind generated waves.  The magnitude of the disturbance causing the tsunami is the primary factor influencing the size and strength of the waves.   The height of the wave when it is generated is very small, usually less than a a metre or two (a few feet).  The distance between successive wave crests or the wavelength however, is much larger than that of a normal wave and may be hundreds of kilometres apart.  Depending on the depth of the water in which the tsunami is traveling, it may attain speeds of up to 800 kilometres per hour (500 miles per hour).

Back to top

Q How does a tsunami behave as it approaches land?

When the waves of a tsunami approach land, their appearance and behavior become dependent on several local factors. Two of the most important factors are the topography of the sea floor (bathymetry) and the actual shape of the shoreline. As a tsunami encounters shallow waters surrounding the shoreline, its height can increase from a metre (3 ft.) or less to over 15 metres (50 ft.). Wave heights can also be increased when concentrated on headlands or when traveling into bays having wide entrances that become progressively more narrow. The presence of an offshore coral reef can dissipate the energy of a tsunami, decreasing the impact on the shoreline. Normal wind swell may ride atop of a tsunami wave thereby increasing wave height.
The image most people have of a tsunami is a large, steep wave breaking on the shore. This image is seldom the case. Most tsunamis appear as an advancing tide without having a developed wave face, resulting in rapid flooding of low-lying coastal areas. Sometimes, a bore can form during which an abrupt front of whitewater will rapidly advance inland much similar to the tidal bore formed at the mouth of large rivers.
Another event that may result from a tsunami is a standing wave or seiche. A seiche occurs in bodies of water that are partially or completely enclosed, creating a standing wave that continually sloshes back and forth. The appearance of a seiche would be very similar to what happens when you place a glass of water on the table; the water rocks back and forth before settling. When a seiche is generated by a tsunami, subsequent tsunami waves may arrive in unison with a seiche resulting in an increase in the drawdown in sea level and a dramatic increase in wave height. Seiche waves may continue several days after a tsunami.

Back to top

Q How long does it take a tsunami to reach land?

Once generated, a tsunami wave in the open ocean can travel with speeds greater than 800 kilometres an hour (500 miles an hour).  These waves can travel across the Pacific Ocean in less than one day.  Locally generated tsunamis can reach coastlines in just minutes.

Back to top

Q How many waves are there in a tsunami?

A tsunami generally consists of a series of waves, often referred to as the tsunami wave train.  The amount of time between successive waves, known as the wave period, is usually a few minutes; in some instances, waves are over an hour apart.  Many people have lost their lives after returning home in between the waves of a tsunami, thinking that the waves had stopped coming.

Back to top

Q What is run-up and inundation?

When a tsunami approaches a coastline, the wave begins to slow down and increase in height, depending on the topography of the sea floor.  Often the first signs of a tsunami are a receding water level caused by the trough of the wave.  In some instances though, a small rise in the water level just before the recession, has been observed.  Regardless, the incoming wave approaches much like the incoming tide though on a much faster scale.  The maximum vertical height to which the water is observed with reference to sea level is referred to as run-up.  The maximum horizontal distance that is reached by a tsunami is referred to as inundation.

Back to top

Q How are tsunami wave heights measured?

The wave height of a tsunami can be highly variable in a local area depending on the underwater topography, orientation to the oncoming wave, the tidal level and the magnitude of the tsunami.  Because direct physical measurement of a tsunami wave would be a life threatening event, a common method for determining tsunami wave height is by measuring the runup, the highest vertical point reached by the wave.  Runup heights are measured by looking at the distance and extent of salt-killed vegetation, and the debris left once the wave has receded.  This distance is referenced to a datum level, usually being the mean sea level or mean lower low water level.  The reference to mean lower low water is more significant in areas with greater tidal ranges such as in Alaska where a smaller tsunami wave can be more devastating during a high tide than a larger wave at low tide. Tide gauges, found in most harbors, are the other tool for measuring tsunami wave height and period (wavelength).

Back to top

Q What is the "wrap-around" effect?

Whether a tsunami is generated in the North or South Pacific, it has the potential to affect all shores of Pacific Islands.  As large tsunami waves approach the islands, they may refract or bend around the islands and diffract through the channels between the islands as well.  The ability of a tsunami wave to bend around and through the islands is called the wrap-around effect.  During the wrap-around effect, the energy of the tsunami often decreases resulting in smaller wave heights.  Sometimes tsunami waves will reflect off of a land mass instead of bending around, thereby increasing wave height of the approaching wave.  Therefore, whether a tsunami warning is issued from an earthquake in Chile, Alaska, or Japan, inhabitants along all shores of the Islands should take the necessary precautions..

Back to top

Q Do all oceans have tsunamis?

Yes.  Tsunamis have been recorded in all the major oceans of the world. However, this phenomenon is mainly seen in the Pacific and the Indian oceans. The Pacific basin is an area surrounded by volcanic island arcs, mountain chains and subduction zones earning the nickname the "ring of fire" and is the most geologically active area on the planet.  The amount of activity in this region makes it much more susceptible to submarine faulting and subsequent tsunami events. The east side of the Indian ocean is also a very active seismic region. The Atlantic and other oceans and seas are far less geologically active, with some exceptions and therefore the occurrence of tsunamis is rare.

Back to top

Q What should I do or not do in a tsunami warning?

Because a tsunami can strike at any time, being adequately prepared and knowing what to do beforehand could save your life. Become familiar with your local civil defense and emergency agencies and their maps of evacuation zones and information on how to be prepared for this type of natural disaster. If you are at the beach and you feel an earthquake or observe a rapid withdrawal of the sea, head for higher ground immediately. When a tsunami warning has been issued do not attempt to use the telephone or head to low-lying areas to view the oncoming waves. Remember, tsunamis travel at very fast speeds across the ocean; therefore once a warning has been issued you should evacuate immediately.

With the CWarn Alarm System you and the people who are with you have the advantage of this critical pre-warning period. Go to places that are higher up. Avoid river valleys. Escaping into higher buildings may offer you protection, however this is not guaranteed as the building could be swept away by the tsunami or collapse.

Back to top

Q If I need to evacuate, what should I bring with me?

Your tsunami survival kit is generally the same for all natural disasters. Here is a list of suggested supplies:  an extra supply of prescription medicines, non-perishable dietary foods, ice chest, a minimum of 2 litres (2 quarts) of water per person per day, pet food, candles/flashlight, matches, blankets/sleeping bags, extra cash, clothing, eyeglasses, personal hygiene items, special items for infants, elderly and disabled family members, quiet games or books/toys for children, important papers-driver’s license, special medical information, insurance policies, and property inventories, First aid kit and water purification kit.

Back to top

Q Can the arrival time of a tsunami be accurately predicted?

When a tsunami is generated offshore the wave will behave as a shallow water wave. A shallow water wave is one that travels through water having a depth less than 1/20 of its wavelength. Knowing that the average Pacific Ocean depth is roughly three miles, oceanographers can determine the speed of the tsunami, and calculate the time it will take to travel between any two points. This information led to the development of travel-time charts that make it possible to predict the arrival time of a tsunami wherever it is generated. Due to the high speeds of these waves, a tsunami can travel across the Pacific Ocean is less than one day! Areas near the epicenter of earthquakes, landslides or volcanic activity are most vulnerable to the effects of a tsunami as they cannot be properly warned by the warning centers of the coming danger..

Back to top

Q I own a boat, what should I do when there is a tsunami warning?

Boats are safer from tsunami damage while in the deep ocean rather than moored in a harbor.  U.S. Coast Guard guidelines suggest deployment to water depths of at least 1,200 feet (370 metres or 200 fathoms).  However, do NOT risk your life and attempt to get underway if it is too close to the first wave arrival time.  Anticipate slowdowns caused by traffic gridlock and hundreds of other boaters heading out to sea. Do NOT go near a harbor if there is a local tsunami..

Back to top