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Vol.
XXIX No. 01
January 02,
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Tsunami
Devastation
Raghu
THE
toll of death and destruction caused by the tsunami waves on December 25 and 26,
mostly in south and south-east Asia but also in far-off Indian ocean islands and
even on the east African coast, continues to rise. As we go to press, more than
30,000 people are believed to have lost their lives, over 15,000 in Indonesia,
7500 in India, 5000 in Sri Lanka, 1500 in Thailand, many hundreds in Malaysia
and the Maldives and several fatalities reported from Myanmar, Bangladesh,
Mauritius, the Seychelles, Kenya and Somalia. The death toll is expected to
climb further as search and rescue teams reach the more remote islands and other
parts of Indonesia and the Andaman & Nicobar group of islands in India. In
India, the worst hit areas have the Nicobar islands and vast stretches of
coastal Tamil Nadu while some coastal areas in Andhra Pradesh and Orissa have
also been affected. The human tragedy in all these countries and regions has
been devastating and the coming days and weeks will reveal not only the extent
of the havoc caused but also the need for relief and rehabilitation.
Whereas
these aspects are clearly the most pressing, and call for immediate attention,
this article attempts to explain the phenomena of tsunamis, examine possible
measures for advance warning so as to minimise loss of life and damage to
property, and look at disaster management in India in the light of past and
present experience.
WHAT
ARE
Tsunamis
or series of huge waves are caused by oceanic earthquakes and related volcanic
eruptions, massive landslides in islands or other coastal landmass, meteorites
striking the sea or by massive undersea explosions. The term itself is of
Japanese origin, literally meaning harbour waves because they strike along the
coast, Japan being the most frequent victim of this natural phenomenon. Tsunamis
are most common in the Pacific ocean which is the planets most
earthquake-prone region rimmed by what is termed the ring of fire of
active volcanoes.
In
contrast, tsunamis are very rare in the Bay of Bengal and Indian Ocean regions.
The present tsunamis were caused by the most massive earthquake in 40 years and
among the four worst quakes in the previous century, registering 9.0 on the
Richter scale, with its epicentre near the northern Indonesian island of
Sumatra. Geologists believe that this megathrust, the highest grade of shift in
the earths crust, was so large that the entire planet must have wobbled
slightly in its orbit! Sumatra is located at a place where several of the
planets tectonic plates (huge sheets of the earths solid crust or
upper layer either on land or beneath the ocean floor) overlap and grind against
each other, accumulating energy over several decades which is then released
suddenly in the form of earthquakes. This particular deep-sea earthquake
released energy equivalent to 1 million Hiroshima-size nuclear bombs and
resulted in the massive tsunami waves.
Not
all earthquakes result in tsunamis nor can one deduce the possibility of a
tsunami from the magnitude of a quake. Earthquakes also originate from different
kinds of tectonic movement. For example, earthquakes along the famous San
Andreas fault running north-south down California in the USA are caused by
tectonic plates slip-striking against each other horizontally. On the other
hand, the earthquake off Sumatra was caused by the Australian and Indian
tectonic plates colliding almost head-on with each other and causing a massive
vertical displacement relative to each other of over 60 feet. This seismic event
took place under 9 km of ocean and along a fault over 1000 km long running
north-south, so the sheer volume of water thrown up can be imagined. It is this
kind of seismic phenomenon that typically results in a tsunami, in this case a
series of massive waves travelling east-west.
A
tsunami is a not a single wave but a series of waves, like the ordinary waves
one sees on a beach. But unlike ordinary waves, which have relatively short
wavelengths (distance between the crests of successive waves) of about 100
metres, tsunamis have wavelengths typically over 500 km and there could be as
much as 2 hours gap between waves. Tsunamis travel across the deep sea at
very high speeds of around 1000 kmph, the speed being a factor of the depth of
the point of origin and the period (time between successive waves). The energy
lost by tsunami waves is inversely proportional to the wavelength i.e. the
greater the wavelength, the less the loss of energy. Therefore, in the deep open
sea, tsunamis lose very little energy and keep travelling at almost constant
high speeds. In deep waters, a tsunami would appear similar to and scarcely
distinguishable from a normal surge in water level. But as they approach a
shoreline, their speed decreases sharply and the shallow depth forces the huge
travelling volume of water upwards into massive waves. The height of these
waves, their speed and ferocity depend a great deal on the contours of the
particular shoreline or continental shelf, and therefore it is quite possible
that some parts of the coast are hit harder while others suffer less damage.
This
particular tsunami was an extremely fast-moving and huge volume of water, the
waves being several hundreds of kilometres wide and travelling at over 1000 kmph.
The tsunami would have hit Aceh in northern Sumatra within minutes of the
earthquake which probably struck Car Nicobar not long afterwards. While Sumatra
is about 1000 km from Port Blair in the Andaman Islands, this is a long chain of
over a thousand islands with the farthest-east Indira Point being just 100 km
from the last Indonesian island. The tsunami must have hit Chennai and the Sri
Lankan coast about 2-3 hours after the quake.
Could
some sort of warning have been given? Could the tsunami have been predicted or
at least suspected? Would a warning or alert have prevented or at least
minimised the massive loss of life in India and other countries in Asia?
TSUNAMI
WARNING SYSTEMS
Soon
after the magnitude of the disaster became apparent by Sunday on December 26
evening, the government announced that India would join the International
Tsunami Warning Programme which she had not so far.
An
international Tsunami Warning System (TWS) was set up by the US National Oceanic
and Atmospheric Administration (NOAA) in 1965 after the disastrous tsunamis
triggered by 9.0 Richter magnitude quakes hit Alaska. The TWS was to cover the
Pacific region and brought into partnership the Pacific rim nations in North and
South America, China, Japan, Thailand and Philippines in Asia, the Pacific
islands (including French islands thus bringing in France also) and Russia. The
system has a Tsunami Warning Centre in Hawaii, located virtually in the middle
of the Pacific and itself a frequent tsunami victim, and is based on 30
seismographic stations to monitor tremors and 70 tidal stations monitoring sea
levels, all relaying readings to the Hawaii centre via satellite.
The
system is triggered by seismic readings suggesting a large earthquake, which
then alerts the system and operators to look for tell-tale tsunami indicators,
particularly rise in sea-levels. However, since correlating these specifically
to tsunamis rather than tidal flows is somewhat problematic, it can take about 1
hour for all the information to be assimilated and analysed, and for a tsunami
warning to be issued (which is said to predict the arrival of the first tsunami
wave to within 10 minutes). Such a time interval would enable evacuation of
coastal areas at a distance of 750 km or more provided action is taken
immediately on receipt of a warning.
In
the present case, if a tsunami warning had been given soon after the quake or at
least when it hit Aceh, there might barely have been time to start evacuating
the Tamil Nadu and Sri Lankan coasts.
However, since tsunamis are rare in the Indian ocean and Bay of Bengal, there
were no tidal sensors in this region and even Thailand, which is a member of the
Pacific TWS has no sensors off its western coast and there are no sensor buoys
in the Indian ocean. The only sensor south of the quakes epicentre registered
only a 2 feet high wave heading towards Australia and the TWS Centre website
issued only a statement to that effect emphasising that no warning or watch
[is] in effect!
It
may be argued that the sheer magnitude of the earthquake and its location should
have at least led to some apprehension of a tsunami. But again the rareness of
the phenomenon in this part of the world meant that leave alone India, no
national, regional or global system responded in this manner. The previous
tsunami in the region had been in 1883 when the famous Krakatoa volcano in
Indonesia had a massive eruption.
For
all its limitations and weaknesses, TWSs have over the years proved their
usefulness in minimising fatalities and casualties.
Over
51,000 people have died in 94 tsunamis during the previous century but the death
toll has dropped sharply after the installation of the TWS in the Pacific
region. In Japan for instance, while over 6000 people died in 14 tsunamis before
the TWS took effect, only 215 fatalities have been recorded in 20 tsunamis since
the mid-sixties.
For
India to have a meaningful TWS, it would not be sufficient to merely join the
existing Pacific-wide system or other regional systems such as the ones being
operated by Japan or around Alaska. There requires to be a system quite similar
to that in the Pacific, with several seismic and tidal sensors in different
littoral nations around the Indian ocean and Bay of Bengal. This will not be
easy and will involve considerable expenditure at the system level. On December
27, Indonesia said it could not afford the tidal sensors whereas the THRUST
(Tsunami Hazard Reduction Utilising Systems Technologies) programme linked to
the NOAA satellite systems have tried out a relatively low-cost option in Chile
costing only $15,000 (Rs 7,00,000) per sensor. Most regional and lower-cost
options rely more on seismic signals and interpretation of the same in
tsunamigenic zones than on actual sea-level readings. Thus lower-cost options
for the Indian ocean region should probably combine automated satellite-based
systems with more conventional real-time communication systems using telephone,
radio etc. Even after the 1964 Alaskan quake, before the TWS was set up, people
in California, alerted by tsunami warnings through conventional means, were able
to evacuate the coastal areas and move to higher ground saving countless lives.
RESCUE
AND RELIEF
But
all the talk in the past few days of TWSs and computerised date-bases of
information linked through satellite and internet places too much reliance on
high-tech solutions and somehow re-affirms the myth assiduously being propagated
in India that, armed with science and technology, it will soon be a developed
country. The harrowing live pictures on numerous television channels showing
villagers helpless, recovering the dead and injured on their own with their bare
hands, without shelter, food or drinking water even 36-48 hours after the
tsunamis struck, should be enough to shatter that myth.
India
needs — desperately and urgently — to get its act together in terms of
simple rescue and relief operations.
After the massive Latur and more recently the Gujarat earthquakes, after the
Orissa super-cyclone, there was much talk of a national Disaster Management
Plan. This seems to have evaporated into thin air as easily as the steel frame
of Indian administration melts in the face of any calamity. Data-bases are all
very well, as are digital diaries, but a simple phone book is also useful and
ready to hand, earth-moving equipment, ambulances, fire-fighting systems all are
essential pre-requisites for disaster management and need not wait for magical
high-tech solutions.
All
warning systems are only as good as the use to which this alert is put.
Effectivity of early warnings depend hugely on the ability of the local
authorities to appreciate danger, to effectively disseminate information to
locals and, of course, on public awareness which needs to be consciously
engendered. In all these areas, India clearly has a long way to go.
We can at least begin by honestly learning from past mistakes and taking earnest
measures to rectify them.
