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1 NeoStencil – Live Online Classes - IAS/IES/GATE/SSC/PSC | +91 95990 75552 | [email protected] Tsunami Tsunami and Its Causes “Tsunami” meaning “harbour wave” in literal translation comes from the Japanese characters for harbour (“tsu”) and wave (“name”). A tsunami also called seismic sea waves, is one of the most powerful and destructive natural forces. It is a series of extremely long waves caused by a large and sudden displacement of the ocean due to earthquake, volcanic eruptions etc. When they reach the coast, they can cause dangerous coastal flooding and powerful currents that can last for several hours or days.
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Tsunami
Tsunami and Its Causes
“Tsunami” meaning “harbour wave” in literal translation comes from the
Japanese characters for harbour (“tsu”) and wave (“name”). A tsunami also called
seismic sea waves, is one of the most powerful and destructive natural forces. It is
a series of extremely long waves caused by a large and sudden displacement of
the ocean due to earthquake, volcanic eruptions etc. When they reach the coast,
they can cause dangerous coastal flooding and powerful currents that can last for
several hours or days.
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Global distribution of Tsunami
Globally, 70% of the confirmed tsunami sources have been in the Pacific Ocean,
9% in the Caribbean Sea, 15% in the Mediterranean Sea and the Atlantic Ocean
and 6% Indian Ocean. Most of these Tsunamis were generated by earthquakes.
Tsunamis are frequently observed along the Pacific ring of fire, particularly along
the coast of Alaska, Philippines, Japan and other islands of South Asia and
Southeast Asia including Malaysia, Indonesia, Myanmar, Sri Lanka and India etc.
Characteristics of Tsunami
Tsunamis are among Earth’s most infrequent hazards and most of them are
small and nondestructive
Tsunamis generally consist of a series of waves, with periods ranging from
minutes to hours
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Tsunamis radiate in all directions from the point of origin and they can cover
entire ocean basins.
There is no season for tsunamis. We cannot predict where, when or how
destructive the next tsunami will be.
Not all tsunamis act the same. And, an individual tsunami may impact coasts
differently. A small tsunami in one place may be very large a few miles away.
Most tsunamis are caused by large earthquakes. Though, not all earthquakes
cause tsunamis.
Tsunamis are waves generated by the tremors and not by an earthquake itself.
The effect of Tsunami would occur only if the epicentre of the tremor is below
oceanic waters and the magnitude is sufficiently high.
A tsunami can strike any ocean coast at any time. They pose a major threat to
coastal communities.
The speed of the wave in the ocean depends upon the depth of water. It is
more in the shallow water than in the ocean deep. As a result of this, the impact
of a tsunami is more near the coast and less over the ocean
Over deep water, the tsunami has very long wavelengths (often hundreds of
kilometres long) when a tsunami enters shallow water, its wave-length gets
reduced and the period remains unchanged, which increases the wave height.
Tsunamis have a small amplitude (wave height) offshore. This can range from
few centimetres to over 30 m height. However, most tsunamis have less than 3
m wave height.
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How is a tsunami different from a wind-generated wave?
Most ocean waves are generated by wind. Tsunamis are not the same as wind
waves. First of all, they have different sources. Also while wind waves only affect
the ocean surface, tsunamis move through the entire water column, from the
ocean surface to the ocean floor. Waves can also be described based on their
wavelength (horizontal distance between wave crests), period (time between
wave crests), and speed. These characteristics highlight the differences between
wind waves and tsunamis.
Tsunami Wind Wave
Source
Earthquakes, landslides, volcanic
activity, certain types of weather,
near earth objects
Winds that blow
across the surface of
the ocean
Location of
energy
Entire water column, from the
ocean surface to the ocean floor Ocean surface
Wavelength 100-500 Km 20-30 meters
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Tsunami Wind Wave
Wave Period 5 minutes – 2 hours 5-20 seconds
Wave Height 10-30 meters from centimeters to
few meters
Wave Speed 800-900 Kmph (in deep water), 30-
50 Kmph (near shore) 10-100 Kmph
Causes of Tsunami
A tsunami is caused by a large and sudden displacement of the ocean. Large
earthquakes below or near the ocean floor are the most common cause. But
landslides, volcanic activity, near earth objects (e.g., asteroids, comets), certain
meteorological conditions and nuclear tests can also cause tsunamis.
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Earthquake – Tsunami can be generated when the sea floor ruptures abruptly
due to tectonic earthquakes, causing vertical displacement of the overlying water.
Most of the earthquakes which generate tsunamis occur on thrust faults. These
earthquakes occur mainly in the areas where tectonic plates move toward each
other in subduction zones.
As per data, ten to fifteen percent of the most damaging tsunamis are generated
by strike-slip earthquakes involving a horizontal movement of the earth.
Example – 2004 Indian Ocean Tsunami was an earthquake-induced Tsunami,
caused by an earthquake (Mw 9.2) in the Indian Ocean.
Landslides – “landslide” is a general term that involves the ground movement of
different types, including rock slide, block slide, debris flows, avalanches, and
glacial calving (referring to the breaking off of large pieces of ice from a glacier).
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Tsunamis can be generated when a landslide enters the water and displaces it.
Such generation of Tsunami depends on the amount of rock material that
displaces the water, the speed with which it is moving, and the depth it moves to.
Landslide-generated tsunamis may be larger than seismic tsunamis near their
source, but they usually lose energy quickly and rarely affect distant coastlines. A
landslide big enough to cause a transoceanic tsunami has not occurred in the
recorded history.
Example – 1998 Papua New Guinea Tsunami was generated by a landslide cause
by an earthquake.
Volcanoes – volcanoes generated Tsunamis are very infrequent, both above and
below water. However, different types of volcanic activity can displace enough
water to generate tsunamis e.g. submarine explosions, caldera formations etc.
Like other non-seismic tsunamis, such as those generated by landslides, volcanic
tsunamis usually lose energy quickly and rarely affect distant coastlines.
Example – 1883 Indonesia Tsunami was caused by the explosion of
Krakatau volcano.
Near Earth Objects – It is very rare for a near earth object like an asteroid or
comet to reach the earth and its potential to generate Tsunami is still uncertain,
as there are no records of a Tsunami caused by near earth objects, in recent
human history. However, scientists are of the opinion there are two ways near
earth objects could generate a tsunami.
Large objects (more than 1,000 meters in diameter) that make it through Earth’s
atmosphere without burning up could hit the ocean, displacing water and
generating an “impact” tsunami.
If this happens above the ocean, the explosion could release energy into the
ocean and generate an “airburst” tsunami.
Meteotsunamis – Some meteorological conditions, for example, air pressure
disturbances often associated with fast moving weather systems, can displace
bodies of water enough to generate Tsunamis. These “meteotsunamis” are
similar to tsunamis generated by earthquakes, but usually with lower energies.
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The development of these Meteotsunamis depends largely on the direction,
intensity of air pressure and ocean depth. Meteotsunamis are regional, and it is
found in some part of the world frequently due to regional factors such as
topography of earth’s surface both below and above the ocean.
Example – 2013 New Jersey, USA Tsunami caused by a high-speed windstorm
associated with thunderstorms.
Nuclear Weapon or tests – it is an example of man-made disaster. Massive
explosions created by a nuclear weapon of nuclear tests have the potential to
cause Tsunami. There have been dangers of using this as a tectonic weapon.
There has been considerable speculation on the possibility of using nuclear
weapons to cause tsunamis near an enemy coastline. In fact, In World War II,
the New Zealand Military Forces, in a failed attempt, tried to create small
tsunamis with explosives.
Effects of Tsunami
After the tsunamis reach the coast, an enormous energy stored in them is
released which causes colossal loss of lives as well as the infrastructure of the
place. As the port cities are economic hubs and densely populated the damage
caused by the tsunami is devastating.
The Tusanami of 2004 in the Indian Ocean is one of the devastating natural
disasters in the modern time. It took a toll of nearly 230000 people leaving in the
coasts of Indian Ocean.
Unfortunately escaping a tsunami is nearly impossible. Hundreds and thousands
of people are killed by tsunamis, most commonly by drowning, electrocution,
explosions from gas and collapsing of buildings etc.
Flooding and contamination of drinking water can cause disease such as Malaria
to spread in the tsunami-hit areas.
Tsunamis not only destroy human life, but also have a devastating effect on
animal and plant life and other natural resources. A tsunami changes the
landscape. It uproots trees and plants and destroys animal habitats.
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Contamination of soil and water is the second key environmental impact of a
tsunami.
There may be nuclear pollution due to radiation resulting from damaged
nuclear plants, as it happened in Fukushima, Japan in March 2011.
Tsunamis are extremely dangerous to coastal life and coastal property. They
produce unusually strong currents, rapidly flooding the land and causing great
damage to coastal property and life.
The flow and force of the water and the debris it carries can destroy boats,
vehicles, and buildings and other structures as the tsunami moves across the
land.
Victims of tsunami events often suffer psychological problems such as PTSD
(Post Traumatic Stress Disorder) which can last for days, years or an entire
lifetime.
Massive economic costs hit communities and nations when a tsunami happens.,
severely affecting the economy of the nation.
Poor nations are more prone to large-scale destruction as the infrastructure are
not well developed, and warning systems are not robust or unavailable. Also,
their ability to cope with such massive disaster remains inadequate.
The water can be just as threatening (if not more so) as it returns to the sea,
taking debris and people with it. Flooding and dangerous currents can last for
days.
Tsunami Early Warning System
Tsunami is the most unpredictable natural disaster in the world and to prevent
the Tsunami is next to impossible. Hence, the only way to effectively mitigate the
impact of a tsunami is through an early warning system.
Tsunamis are detected in advance using a tsunami warning system (TWS) and
early warnings are issued to safeguard the life of people. It is made up of two
equally important components: a network of sensors to detect tsunamis and a
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communications infrastructure to issue timely alarms to permit evacuation of the
coastal areas.
There are many regional and international early warning systems installed all
across the globe. National governments warn citizens through a variety of means,
including SMS messages, radio and television broadcasts, and sirens from
dedicated platforms, mosque loudspeakers and police vehicles with loudspeakers.
India had volunteered to join the International Tsunami Warning System after the
December 2004 tsunami disaster. The Indian Tsunami Early Warning Centre
(ITEWC) embedded with specific systems called Deep Ocean Assessment and
Reporting of Tsunamis (DART), established in 2007 at Indian National Centre for
Ocean Information Sciences, (INCOIS – ESSO) Hyderabad, autonomous body
under Ministry of Earth Sciences, is up and running to provide tsunami advisories
for the events occurring in the global oceans.
It has been recognized as one of the best systems in the world. The ITEWC
includes a real-time seismic monitoring network of seventeen broadband seismic
stations to detect tsunamigenic earthquakes and to provide timely warnings to
the vulnerable community. It also receives earthquake data from all other global
networks to detect earthquakes (of M>6.5).
Since its inception in October 2007, so far ITEWC has monitored 339 earthquakes
of M > 6.5. ITEWC also acts as one of the Regional Tsunami advisory Service
Provider (RTSP) along with Australia & Indonesia for the Indian Ocean region.
Way forward and recommendation
2004 Indian Ocean Tsunami was a brutal reminder of disaster preparedness in
India. While the current early warning system in India is state of the art, it is still
inadequate in terms of preparedness for Tsunami. Following suggestions can be
observed for enhancing India’s preparedness for future Tsunami events:-
Adopting integrated multi-hazard approach with emphasis on cyclone and
tsunami risk mitigation in coastal areas
Strict implementation of the coastal zone regulations
Plantation of mangroves and coastal forests along the coastline
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Identification of vulnerable structures and appropriate retrofitting for tsunami
resistance of all such buildings as well as appropriate planning, designing,
construction of new facilities
Capacity building programmes and public awareness campaigns should be held
at Tsunami prone areas
Streamlining the relief distribution system and evacuation plans in Tsunami
prone areas
Component of planning for reconstruction and rehabilitation should be added
to disaster management plans at all levels
Emphasis on mental health and to socio-psychological issues during post-
disaster period should be accorded in every plan
Conclusion
Tsunami is one of the most hazardous and unpredictable natural force. Tsunamis
have no seasons and they can occur at anytime and anywhere. We certainly
cannot prevent Tsunami. But what we can do is take necessary steps to minimize
the damage caused by it. Tsunami is a global and transnational event. Hence, it is
important that all countries across the world should join hands to evolve new
scientific ways to predict Tsunamis and to design mitigation strategies to cope
with this disastrous force.
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