Marine disasters are natural disasters happened in the sea, which can change drastically from normal marine environment. Marine disasters include those happened from coastal lines to the oceans. Just like any other disasters, marine disasters are very dangerous to human, give huge negative impacts to social, economy, properties, and life events.
See also: Effects of Ocean Currents
Theer are several marine disasters which commonly happened, as follows:
Tsunami is series of long waves that rise because of sudden and impulsive changes in water body and seabed, caused by earthquakes, eruption of seabed volcanoes, seabed slides, gas extrusion from volcanic mud, iceberg collapse, nuclear explosions, even by falling objects from the space.
Tsunami speed depends on the depth of the water. In deep seas, tsunami can move with the speed of 500-1000 kilometers/hour. While in shallow seas the speed is much reduced to only a few dozens kilometers/hour.
Tsunami height also depends on the depth of the water. In deep seas, tsunami amplitudo only reaches 1 meter high, but in coastal line the amplitudo can be as high as dozens of meters.
According to the source and distance of seizure, tsunami is divided into:
- Far-field tsunami: the distance of source is more than 1000 kilometers and pass the continental shelf Regional tsunami: the distance of source is between 100 – 1000 kilometers
- Near-field tsunami: the seizure source is in continental shelf, with distance less than 100 km.
Damages and destructions caused by tsunami are direct results from brunts of tsunami waves and currents, while fatalities are caused by drowning in tsunami waves. Strong currents also cause erosion in foot of building foundations, collapse of bridges, dragging houses, and turning vehicles upside-down.
Severe damages are also caused by floating rubbles (including ships, cars, and trees) which can be dangerous when hitting buildings, docks, and other vehicles. Another damage take form of fire caused by oil spills or explosion from wrecked ships during tsunami. Following dangers caused by dirt pollution and chemical substances transported by tsunami and pollute clean water resource.
2. Stormy Waves
Stormy waves are waves created by very powerful wind, with the speed of wind more than 91 kilometers/hour, wave height 7-30 meters. This kind of waves is very dangerous for sailing and housing/building around coastal line, and also can cause beach abrasion. For example: storm, typhoone/hurricane.
Stormy waves happen following storms or very powerful wind blows in the sea (meterology phenomenon), the wave height can be dozen meters around wind sources, and the waves keep going as long as the wind blows, and subside along with the wind blows over.
According to instigatuon mechanism, this stormy waves phenomenon only happens in certain times, linked with certain wind seasons, and will only happen in certain locations.
The stormy waves phenomenon occurs, linked with meteorology phenomenon in the form of wind blows which probably happen regularly each year, according to climate and season changes. So, prediction and early warnings of stormy waves are easier to do than prediction and early warnings of tsunami.
About the destructive nature of these stormy waves, the destructive capabilities are much smaller compared to tsunami. However, for certain conditions in certain places, stormy waves can be very powerful, like the one happened at 11th June 2007 in Nobbys Beach, Newscastle, Australia. The stormy waves happened in that coastline could strand a ship carrying coals as much as 30.000 tons onto the beach.
3. Rising of Sea Level
Rising of sea level is a phenomenon that causes the rise of sea surface onto coastal line because of some factors.
The increasing of green house gases emission like carbondioxyde (CO2), methane (CH4), dinitrooxyde (N2O), and chlorofluorocarbon (CFC) to the athmosphere leads to green house effects.
In which causes trapped sun ray radiation which should be reflected by earth surface into athmosphere, causing rising temperature of earth surface and athmosphere until it reaches new balance.
The amount of heat going in and out of athmosphere does not change, but the amount of heat that is trapped inside the earth and athmosphere is rising, causing the rise of temperature if earth surface and athmosphere.
The Rising of Sea Level Effects
Global warming is considered to give significant effect to the rising of sea level in this 21st century. The physical effect of rising of sea level is the increasing frequency and intensity of flood because of dike effect by the rising of sea level.
This dike causes the decreasing of flow rate of the rivers in estuaries, sedimentation rate will increase, thus causing silting in estuaries.
Silting estuaries and rising of sea level will increase frequency and intensity of flood around estuaries. Meanwhile, there are several effects of sea level rise, as follows:
Pullback of Coastline
Rising of sea level also causes pullback of coastline because of the stagnant sloping shoreline, loss of mangroves, and increased shore erosion. Erosion on the shore will be much bigger because the waves can get far into the ainland because of the rising of sea level.
The rising of sea level also can sink small islets. Intrusion of sea water into the mainland is a serious problem in coastal area. The utilization of ground water that does not count land balance can cause decline of ground water level, which can ease the intrusion of sea water into ground water.
The rising of sea level also causes more sea water volume intrudes rivers. The sea water that intrudes far into the mainland through the rivers is a big problem for people in coastal area who depend their freshwater intake from the rivers.
Increase the Height of Waves
Rising of sea level also gives impact to security of buildings around the coastline. The rising of sea level increases the height of waves and increases over-topping frequency towards buildings on the shore, thus the security of buildings would decrease. Rising of sea level also gives impact to coastal line ecosystem as the salinity would increase.
The increasing in salinity caused by the rising of sea level causes mangroves to migrate t mainland area, the place with less salinity. All species in coastal line which cannot adapt to high salinity would die. The rising of sea level is not only caused by global warming but also by other factors such as tides, land subsidence, stormy waves or stormy tide waves, La Nina, and tsunami.
4. El Nino and La Nina
El Nino, according to history, is a phenomenon observed by citizens or fishermen in Peru and Ecuador who live in the shore around east side of Pacific Ocean during December.
The observed phenomenon is the increasing of sea surface temperature which is usually in cool temperature.
This phenomenon caused the water which was initially fertile and contains plenty of fish (as a result of upwelling which brings many nutrients from the bottom) became the opposite.
In later time, the scientists also found out that other than the phenomenon of increased sea surface temperature, there is the opposite phenomenon where the sea surface temperature decreases because of the increased upwelling. The opposite of El Nino is then called La Nina.
These phenomena have 2-7 years periods. So, according to the explanation above, we can undertand that El Nino is a phenomenon where there is the increased sea surface temperature which causes upwelling, and usually the indication is prolonged dry season. Meanwhile, La Nina is a phenomenon where there is decreased sea surface temperture because of increased upwelling, and usually indicated by prolonged wet season and frequent floods in an area.
See also: Acidification of The Ocean
5. Beach Abrasion
Beach abrasion is beach erosion by continous blows of ocean waves toward beach wall. Today, the mainlands lose the lines about 5-30 meters per year because of abrasion.
Abrasion causes damage and loss of mangroves, plantations, aquacultures, and people’s houses around coastal line.
In more detail, the causes of beach abrasion are:
A. Land Subsidence
Excessive pumping of ground water for both industrial and drinking water purposes around coastal area will cause land subsidence, especially if the beach land is composed mainly by clay/mud because the physical characteristic of clay/mud which can change easily according to water concentration.
Land subsidence decreases water pressure in land pores. This causes flood and later will increase erosion and beach abrasion. This shows that land subsidence potency is adequately big and give contribution to flood during high tides.
B. Damage of Mangroves
Mangroves are included in sustainable resources and the main important framer of ecosystem which supports the life around coastal line. Mangroves have important function as natural protector of the beach because of its solid roots which can reduce waves and hold sediment. This means it can act as land cruiser. What a pity that mangroves are getting scarce today, because people use its woods as fuel and building materials.
Read also: Climate of the Ocean
C. Damage by Hydrodynamic forces of Ocean Waves
Beach orientation which is relatively perpendicular or parallel with the crest of a dominan wave gives information that the beach is in dynamically balanced condition. The waves condition which is usually straight will be bent because of refraction/difraction and shoaling process of the waves.
The beach will respond by orientating itself in such a way so it keeps perpendicular to the waves directions, or in other words, there are erosion and sediment deposition until it reaches new balance, and the next happening process is only perpendicular transport of the beach (cross shore transport).
Read also: Ocean Natural Resources
D. Damage Caused by Other Natural Causes
Other natural causes includes global climate changes and extreme events such as tropical cyclone. Another factor is the rising of sea level caused by global warming (green house effect) which causes increasing wave heights.
E.Damage Caused by Human Activities
Human activities which can damage the shore are sand mining on the beach, buildings that jut into the sea, and making aquacultures without taking care of condition and location.
See also: Ocean Pollution
Flood is a river water flow which is relatively bigger than usual/normal as a result of continous heavy rain in the upstream or other places, so the water cannot be accomodated in existed ravines, and the water overflows and flood the surrounding area.
Other than river flows, flood can also happen because of water flows from the sea as a result of storm or tsunami.
Mitigations of Disasters
Mitigation of disasters are a series of efforts to decrease the risks of disasters, both by physical buildings and education of awareness and improvement of ability to face the threat of disasters.
1. Forms of Mitigation:
- Structural Mitigation: building checkdam, dams, river embankments, earthquake-ressistant houses, etc.
- Non-Structural Mitigation: legislation, making new laws, trainings and education about disasters, etc.
2. Disaster Management:
- Alertness: A series of activities which is done to anticipate the coing disasters through organizing and through appropriate steps, effectively and efficiently. For example: communication setup, command posts, evacuation site preparation, contingency plans, and socializing the rules / disaster management guidelines.
- Emergency Response: Efforts that are done immediately during the onset of disaster, to cope with the empact of disasters, especially saving the lives and properties, evacuation and refuge.
- Emergency Relief: efforts of providing assistance associated with basic human needs, such as foods, clothes, temporary helters, health service, sanitation and clean water.
- Recovery: An emergency recovery process of the condition of people who suffers from disasters, by immediately functioning facilities and infrastructures into its original state. The efforts that can be done is to repair infrastructure and basic service (roads, electricity, clean water, health service, etc.)
- Rehabilitation: Efforts and steps done after the onset of disasters, to help people repairing their houses, important public and social facilities, and revive the economy.
- Reconstruction: medium-term and long-term programs to improve physical, social and economy and restore the community life into the same condition or even better than before.
See also: Ocean Plants
Mitigation of Marine Disasters
There are several mitigation of marine disasters, such as:
The implementation of disaster risk management need to be done systematically through administrative policies, organizations, operational, strategy, and implementation capability and the ability of communities to face the disaster, to reduce the dangerous impact of disasters. The disaster risk management reviews all activities both in structural measures and non-structural measures to prevent or to decrease the effects of tsunami.
The structural measures are done for:
- Increasing the awareness toward tsunami risks in communities and introduce local actions needed to be done to reduce the risk of tsunami. (Read also: Waves in Ocean)
- Stimulating the alertness of planners both in national and local levels to implementate national development plannings which are familiar with tsunami, especially in tsunami-prone areas.
- Helping politicians, goventments, and legislatives to understand the characteristics of each risk faced by communities and helping to understand the impacts of the disaster.
- Demonstrating the ways and its meanings while reducing the risks, in national and local scopes, by proper policies and plannings.
2. Rising of Sea Level
Governments must do mitigation efforts of rising of sea level by preparing vulnerability maps and maps of immersion risk caused by rising of sea level.
To reduce the impacts of the disasters, mitigation is done both physically (structurally) and non-physically (non-structurally). Physical mitigation is done by technical efforts, both artificially and naturally; while non-physical mitigation involves adjustments and settings of human activities to be consistent and appropriate with mitigation efforts both physically and other efforts.
In efforts of minimizing impacts of rising of sea level, there are 3 adaptive strategies:
- Retreat: leaving the areas vulnerable of immersion caused by rising of sea level, and re-doing spatial arrangements.
- Accomodation: adaptation toward environmental changes caused by immersion, such as building houses on stilts, modifying drainage system, etc.
- Protection: defensive acts to protect costal areas from immersion, sea water intrusion and the missing natural resources caused by rising of sea level. Protection strategy is done by building dikes or seawalls.
3. La Nina and Flood
To tackle La Nina (and flood is usually caused by La Nina), things that must be done are building dikes, restoration / reforestation of deforested forests to expand water catchment, and controlling waste management (prohibiting people to throw garbage into rivers or streams).
4. Beach Abrasion
To tackle and prevent beach abrasion, the mitigation takes forms in these:
Preservation of Coral Reefs
One of the functions of coral reefs is to reduce waves forces which hit the beach. Because of it, preservation of coral reefs is needed by making rules and laws to protect its habitat. Coral reefs ecosystem, seagrass, mangroves and other beach vegetation is the natural defense which is very effective in reducing the speed and energy of ocean waves, so it can prevent beach abrasion. If beach abrasion happens in small islets located in open ocean, the drowning process of the islets would be much faster.
Preservation of Mangroves
The main function of mangroves is to break waves that hit on beach, and strengthen the coastal land. More than that, mangroves also functions as breeding place of fish and crabs.
Increasing Capacity of Coastal Area
Increasing Capacity is the most realistic solution to reduce the abrasion risk in coastal area. Increasing capacity of coastal area to reduce the risk of abrasion must be done comprehensively and there must be a strong concession between all interested parties. Without any concession, the increasing of capacity cannot be done effectively. Increasing of capacity can be done by adaptation, mitigation, and innovation to create a strong coastal area. From the 3 ways above, mitigation is the efforts that can be developed and applied the skills.
Reducing Hazard and Vulnerability
Hazard of abrasion risk is very difficult to be reduced, while Vulnerability is not easy to be implemented. Reducing Vulnerability is done by limiting or prohibiting any community to do activities or live in coastal area. This is very difficult to do because it will risen many problem, especially social conflicts.
Building Wave Breakers
In beaches that are already or almost affected by abrasion, builidng wave breakers is very necessary to reduce the impact of waves. This effort can be included in technical mitigation of disasters.
Prohibition of Mining of Beach Sand
Beach sand that is taken continously will reduce the beach strength.
Some countries are archipelagos, consisted of small islands and islets. These type of countries are prone to marine disasters, as they are mostly located in open ocean, which allows disasters to happen suddenly. The marine disasters can be tsunami, stormy waves, rising of sea level, el nino and la nina, flood, and beach abrasion.
When these marine disasters happen, no doubt they will take a lot of casualities as well as material losses. Becaus of that, we need some knowledge about mitigation of disasters, especially marine disasters, so we can do proper actions before the disaster happens, during disasters, and after the disasters.