Waves of Change
By Sophia Read
For The Bali Times
SEMINYAK ~ Tsunami. Now thereâ€™s a word we have all heard enough of it the past week or so. Just for the record, there wasnâ€™t one.
The lack of a tsunami should not lessen our sympathy for those affected by the earthquake â€“ an estimated 10,000 people lost their homes or livelihoods throughout the affected zone, and the major hospital serving the area was also damaged. There were several quakes: the first and the strongest measured 8.4 on the Richter scale; the epicenter was off the coast of the island of Sumatra. The aftershocks were also devastating in their own right â€“ on Thursday morning a shock was measured at 7.8.
Tsunami warnings were issued in a wide range of countries all around the Indian Ocean, and the news that another tsunami, comparable to that which devastated the area in 2004, reverberated around the globe. Here in Bali, we were contacted by people from as near as Singapore, and as far as Iceland, all asking whether they should cancel their holidays, whether it was still safe.
In the event it was, but, worryingly, the warning system installed in Padang completely failed to work. A recent education campaign, combined with warnings issued from the loudspeakers from mosques, meant that the inhabitants evacuated in relative order, and luckily, the city escaped serious damage.
But what about next time? And there will be a next time.
Tsunamis are frequently and incorrectly referred to as â€œtidal waves.â€ In fact, they have nothing whatsoever to do with the tide, and are not really even waves in the normal sense (waves are caused by wind effecting water). The word comes from the Japanese term, which translates as â€œharbor wave.â€ It is a much apter term, as tsunamis have little effect in the deep ocean – often passing unnoticed by ships at sea â€“ but when they reach harbor, their effect is catastrophic.
They occur when an event causes a massive body of water to displace in the ocean. This force is most commonly earthquakes, but could be a landslide, or, more rarely, the impact of a meteorite, or even the test of a nuclear weapon (thereâ€™s another good reason not to). The most common cause of a tsunami is a subduction earthquake. Subduction zones (high school geography, anyone?) are the boundaries between two tectonic plates, where the plates are moving towards each other, and one (normally the oceanic) is forced under the other (normally the continental). Here, right in the volcanic â€œRing of Fire,â€ we are perched on top of one of the most active subduction zones on the planet.
But not all subduction earthquakes cause tsunami, and, as we as yet have no completely effective or accurate way of predicting earthquakes, tsunami prediction is difficult, to say the least. Several conditions must be fulfilled for an earthquake to cause a tsunami.
First, and most obviously, the earthquake must occur along a fault line (where the two plates meet) that is either on the ocean floor or close to the ocean. Secondly, a massive volume of water needs to be displaced by the force of the shake â€“ a vertical movement of several meters over an enormous area â€“ hundreds and hundreds of square kilometers. To predict the volume of water that will be displaced by an earthquake is almost impossible â€“ hence the issuing of tsunami warnings, even though no tsunami materialized.
To quote the Intergovernmental Oceanographic Commission, â€œthe only known method to quickly recognize a tsunami earthquake is to estimate a parameter called the seismic movement using very long period seismic waves (more than 50 seconds/cycle). To do this, obviously, said event must have already happened. Computer models can predict the path of a tsunami, if they have the precise measurements of the event that caused it, based on models of the ocean floor and the surrounding land.â€
However, given that a tsunami can strike only minutes after an earthquake, and that the speed at which these waves travel can cross oceans in a single day, we are all bound to feel horribly at risk. Tsunami can travel at 800 kilometers an hour when in the deep ocean, but it is only when they reach shallow water, slow down and all that enormous quantity of water rises up that we see the classic â€œwall of water.â€ They have been measured up to 30 feet in height, but a height of much, much less than that can still ravage whole countries.
Research into past events (Paleotsunami research â€“ try saying that quickly five times) is adding to the store of knowledge available about the effects of tsunami. Advances in technology, including the availability of satellite technology to enable the real-time collation of massive amounts of data, are gradually increasing our ability to predict tsunami, and therefore to hopefully minimize the damage they cause.
So, rules to follow in the event of a tsunami:
Hopefully, everyone should be aware of the approaching wave, but if there is no warning, here are some things to be aware of.
A tsunami is a series of waves, there may be up to an hour between each wave and the first one is not necessarily the biggest.
The first sign may well be the ocean receding. This is not a time to run out and gather interesting items exposed to the light of day. If you see the ocean leaving the shore, turn your back and move in the opposite direction as fast as you reasonably can.
If you have ever played chicken in the waves, you should be aware of this â€“ the ocean can move faster than you can. If you have a chance, move away, fast – photographs may be a good souvenir, but not if you are not alive to enjoy them.
And last, but not least, in Bali â€“ surfers, please be aware, itâ€™s not a good wave; donâ€™t try and surf it!
The key to preventing loss of life and minimizing damage lies in education, and in preparation. That the newly implemented Tsunami Warning System in Padang failed to work is, to put it mildly, disappointing. Some 300,000 people died because of the 2004 tsunami. That should be enough.
The writer is sales manager of AquaMarine Diving â€“ Bali.Filed under: The Island