Tsunami is adopted from Japanese language. It came from “tsu” means harbor and “nami” that is means wave. The meaning of Tsunami is literally a ” big waves at the harbor”. The tsunami is the movement of water of sea that is caused by sudden sea level changes in the ocean.
Sea level changes can be caused by earthquakes that is centered under the sea, submarine volcanic eruptions, submarine landslides, or meteor that hit the sea. The Greek historian, Thucydides was the first to link the tsunami to an undersea earthquake.
see also: Facts of Dead Sea
However, until the 20th century, knowledge about the cause of the tsunami is still lack. Research is still underway to understand the causes of tsunami. Tsunami can occur in the event of a disturbance causing large volumes of water, such as volcanic eruptions, earthquakes, landslides and meteors that fall to the earth. However, 90% of tsunami are the result of submarine earthquakes. In the historical record of several tsunamis caused by erupting volcanoes, for example when the eruption of Mount Krakatau.
A vertical movement in the earth’s crust may cause the seabed to rise or fall suddenly, resulting in a disruption of the water’s balance above it. This resulted in the huge flow of sea water energy. When it reached the shore, the energy transform into a large wave that resulted in a tsunami. (see also: Sea Erosion)
This vertical movement can occur on earthquakes that is also common in below areas, where oceanic plates slip beneath continental plates. Landslides that occur on the seafloor and the fall of a volcano can also lead to disruption of sea water that can produce tsunami. An earthquake that causes the motion perpendicular to the earth’s layers. As a result, the seabed fluctuates suddenly so that the balance of sea water above it is disrupted. Similarly, cosmic objects or meteors that fall from the top. If the size of the meteor or landslide is quite large, mega tsunami can occur that reach hundreds of meters high. (see also: Ocean Plants)
Here explanation about Causes and Effects of Tsunami.
Causes of the Tsunami
The source of the plant is known that 90% of the tsunami is caused by tectonic earthquake activity, 9% due to volcanic activity and 1% by soil landslides that occurring in water such as in the lakes or in the ocean or landslides that came from land which is enters to the ocean. (see also: Ocean Layers)
Tsunami is a series of long waves caused by sudden massive water movement. Tsunami can be triggered by earthquake events, volcanic eruptions, and avalanches on the seabed, or landslide in large volumes, the impact of meteors, and the collapse of the coastal slopes falling into the sea or the bay. (See also: Ocean Pollution)
Earthquake is earth shaking caused by the collision between earth fragment, active volcanic activity or rock fall. Earthquake strength due to volcanic activity and rock collapse is relatively small, so we will focus the discussion on the earthquake as a result of intercollision between earth fragment and active faulting. (See also: Marine Energy)
Tectonic earthquakes are the most damaging types of earthquakes that occur because of the release of energy stress that buried inside the rocks due to internal movement. The characteristics of the earthquake that caused the tsunami is:
- Earthquakes centered on the sea and shallow (0 – 30 km).
- An earthquake with a strength of at least 6.5 on the Richter Scale. (see also: Marine Disasters)
- An earthquake with a fault pattern rises or a fault decreases. (see also: Effect Of Sea Level Rise)
Causes of Tectonic Earthquakes
The cause of tectonic earthquake is due to tectonic effect of movement of the earth’s plates and cesarean activity of the surface of the earth and local geomorphological movement, for example the occurrence of activity volcanoes, nuclear explosions. (see also: Endangered Seahorses)
Potential tsunami earthquakes are earthquakes with centers earthquake on seabed which is had magnitde of earthquake is > 7 SR with depth less than 60-70 Km. And also there is the vertical deformation of the seabed that is formed because of the magnitude of earthquake is greater than 6,0 Richter Scale as well as the type of falling faulth (normal faulth) or broken fault (Thrush faulth). (see also: Ocean Phenomena)
Tsunami which caused by tectonic earthquakes are affected by depth of the source of the earthquake as well as the length, depth, and direction of tectonic fracture. In general, new tsunami may occur if the depth of the epicenter is less than 60 km across below sea level. Immediately, after the earthquake happened the tsunami will raised to all direction. (See also: Ocean Problems)
During propagation, the wave’s height is greater due to influence of of the sea floor. When it reaches the shore, the water mass will propel up and headed to the mainland. When high tsunami waves reaching the shore, it is greatly influenced by the contours of the seabed around the coast. Otherwise, if the distant tsunami go to the land, it is strongly influenced by topography and the usage land in the coastal area.
The lack of capability in anticipating disasters can be seen from spatial planning that haven’t optimal yet and development planning that pay less attention to disaster risk. Lack of track facilities and evacuation sites for the citizens are also one example of a lack of ability to deal with disaster. The hazard maps and risk maps that have been created haven’t be used optimally in integrated disaster risk reduction and development programs.
There is a tendency that the Disaster Risk Reduction Program (DRR) only considered as an additional cost, not part of a development investment that can ensure sustainable development. For that, a potential earthquake that can cause Tsunami should be given more attention. (See also: Ocean Environment
Effects of the Tsunami
The tsunami waves can propagate in all directions. The power contained in the tsunami wave will determined the height and the speed of the Tsunami wave. In the deep ocean, tsunami waves can travel at speeds of 500-1000 km per hour. This speed is equal to airplane’s speed. However, in the deep sea, the tsunami wave height is only about 1 meter. That why, the power of tsunami wave is not felt by the ship that was in the middle of the sea.
When approaching the coast, the tsunami wave velocity decreases to about 30 km per hour, but its height has increased to tens of meters. The waves of the Tsunami can enter up to tens of kilometers from the shore. Damage and casualties caused by the tsunami can be caused by the blow of water and materials carried by the tsunami wave. The negative impacts caused by the tsunami are destroying whatever it takes. Buildings, vegetation, and human casualties and causing puddles, contamination of saltwater to farmland, soil, and fresh water.
The meaning of impact according to KBBI is the impact that have both positive and negative consequences. Influence is the power that is exists and arise from something (people, objects) that come to form character, belief or one’s deeds. Influence is a state where there is a obstacle relationship behind or causal relationship between what affects and what is affected. (see also: Effects of Greenhouse)
The impact of disasters on health is the occurrence of health crises, which raises:
- Mass casualties – Disasters that occur may result many deaths and injury, trauma and disability victim
- Displacement – This evacuation may occur as a result of the destruction homes or the danger that can occur if they remain in the location events. This is influenced by the risk level of a region or region where the occurrence of disaster. (See also: Marine Protected Areas)
A. Based on the Positive Impact of the Tsunami
- Tsunami is a natural disasters caused many death victims, so that employment became widely open for people who is still alive. (See also: Deep Ocean Ecosystems)
- Cooperate and work together to help victims of disaster, causing an awareness effect that humans are mutual creature that need each other to live. (See also: Sea Salt Facts)
- We can know the quality of the construction of our buildings and their weaknesses and can make new innovations. So, if the disaster comes back the new construction will strong enough to stay still until the disaster go away. (see also: Waves in Ocean)
B. The Negative Impact of the Tsunami Disaster
- Destructive what the course of the building, the plants, and the resulting loss of life human as well as causing inundation, saltwater pollution of farmland, soil, and clean water.
- Many skilled workers are victimized so it is difficult to seek more appropriate experts in their field of work.
- The Government will overwhelmed in the implementation of post-disaster development because of the lack of funding factor and too much expenses needed. (see also: Ocean Coral Reef )
- Increase the level of poverty in the event of disaster-affected communities who lost everything.
Ways to Reduce Tsunami Risks
The tsunami resulted in high energy difference. The difference of energy cause the wave with high speed. This wave has a strong damaged power. To reduce the damage and the casualties caused by tsunami, the coastal areas need protection. However physical protection is almost impossible to do as it will requires a huge cost. The protective construction will only work effectively to protect the bay that has a narrow beach. The protective construction must be strong enough to accept tsunami wave pressure, and high enough to avoid wave overtopping it. There are more ways that effective to train the population in the face of the tsunami and avoiding construction in areas often hit by the tsunami. The following actions need to be taken to reduce disaster risk tsunami.
- Establish an early warning system.
- Relocation of resettlement areas prone to tsunami threats. (See also: How to Prevent El Nino)
- Education to the public about various things related to the tsunami, such as arrival signs tsunami and ways of self-preservation, so that the community is ready and responsive If at any time the tsunami comes suddenly.
- Make a path or a path to escape the tsunami. (See also: Acidification of The Ocean)
- Planting coastal areas with plants which can effectively absorb wave energy (eg mangroves) let the field open to absorb the tsunami energy.
- Make dike or breakwater in possible areas. (see also: Volcano under the Ocean)
The Mechanism of Tsunami
The mechanism of tsunami that is caused by earthquake can be described in four phase including initial conditions, wave separation, amplification, and wave invasion.
1. Initial Conditions
Earthquakes are usually associated with surface shocks that occurs as a result of the propagation of elastic waves through the rock base to ground level. In areas that adjacent to sources of seismic earthquake (fragment), the seabed will be partially uplifted permanently and the other part is down-dropped, so it will push the water column to move rises and falls. (See also: Salinity of Ocean Water)
On the other hand, the potential energy that caused by this water is turned into a tsunami wave or kinetic energy above the elevation of mean sea level. This energy will propagates horizontally. The case above is a basic collapse of the continental slope caused by an earthquake with the relative deep oceans . This case can also occur in a fragment collapse of continental with shallow water depths due to earthquake. (See also: Effects of Ocean Currents)
2. Separation of Waves
After a few minutes of earthquake events, the initial wave of the tsunami will be separated into tsunamis that propagate into the ocean, this tsunami is called distant tsunami and the other part of initial tsunami wave is propagate to the adjacent beaches, we call it as local tsunami. The height of this two type tsunami is about a half the height of initial tsunami wave. The speed of propagation to these two tsunami waves can be estimated as the root of The depth of the sea (gd). Therefore, the tsunami velocity in the deep ocean will be faster than the local tsunami.
3. Amplification and Wave Invasion
At the time of local tsunami propagate through continental slopes, there are some frequent event such ad increase the wave amplitude and decrease in length of wave. After approaching the land with a more upright slope, there will occur a wave invasion. At the time the tsunami waves propagate from the depth water sea, it will pass through the part of the continental slope that near to the shore and there will be a wave invasion of tsunami. Wave invasion of tsunami is a measure of the height of water level on the beach against sea level, the average of this height is being used as a reference. (See also: Ocean Animals)
From the observation of various tsunami events, the tsunami generally doesn’t cause a high waves to rotate locally like the wave that usually used by the surfer for surfing on ocean. However, the tsunami came in the form of strong waves with high speed in different terrain as described in amplification, So that the first wave invasion isn’t the highest rhythm. (see also: Endangered Sea Turtles List)
Signs of a Tsunami
- Land movement
This land movement arises because of the propagation of waves in the solid layer of the earth due to the earthquake. If a large shallow earthquake happens below sea level, it is very potential tsunami. Especially for the tsunami near field (the source close to the beach), this movement can be felt directly by the human senses without using a measuring device. For a tsunami with source far field (remote source with beach) the movement can’t felt by the human senses. (See also: Types of Sea Urchins)
- Tsunami Forerunners
Nakamura and Watanabe define Tsunami forerunners as a series of oscillations or the sea level that preceded the arrival of the main tsunami, that easily can be seen on tape station recordings with typical amplitude and smaller periods. But, this tsunami forerunner not always appearing before the real Tsunami.
In North and South America, the tsunami forerunners not present due to Natural slope from the initial tsunami to the beach. While the presence of forerunners tsunami in other area such as Japan is due to the occurrence of resonance (wave following) of the initial tsunami at bay and in continental exposure before the main tsunami came.
- Withdrawal Forward or Initial Withdrawal Bore
In some writings both popular and scientific suggest about the presence of withdrawal of sea level before the main tsunami reaches beach. From the results of the tsunami recording, Murty (1977) suggests there are hundreds of cases where the withdrawal of this ocean surface occurs, but in some instances not present. Theoretically, this kind of situation is generally caused by the advance of the previous negative wave followed by the positive wave.
- High Sea Water Front Wall In The Sea (Tsunami Bore)
Tsunami bore is a tsunami movement that spreads in shallow waters. Tsunami bore will continues to spreading over the coast as split waves that shaped like the wall with almost flat height. This phenomenon is due to meteorological disturbance such as gravity of the moon. (See also: Surface of Tension Liquids)
- The Incidence of Strange Voice
Many old documents in Japan reported abnormal sounds before the arrival of the tsunami, it is engraved on the Tsunami Monument in the Prefecture Aomori which reads: “Earthquake, sea Roar, then Tsunami” (Earthquake, Roaring, then tsunami). This monument was built after the 1993 Showa Great Sanriku Tsunami, aims to continue the attention of the people of that generation will come against the tsunami. It recommends to evacuate if sounds abnormal after an earthquake. A voice like this is also told by tsunami witnesses in Biak, Banyuwangi and Flores which mentions sounds that resemble: the sound of helicopters, sounds drum bands, as well as the rocketing sound of the rock. ( See also: Climate of the Ocean)
- Observation of the sense of smell and sense of taste
Eyewitnesses suggested that the time before the tsunami came wind with a rather cold air mixed with the smell of sea salt is strong enough. This is most likely due to sea saline offshore which in huge amount going to the seashore. So, the smell of the salt is so strong. (see also: Global Warming in Ocean)
Those are complete explanation about Causes and Effects of Tsunami.