Wednesday, September 30, 2009

Tsunami Disaster in Japan

On the afternoon of March 11th 2011 a massive tsunami was generated by an estimated 8.9 intensity earthquake that occurred out to sea about 380 km to the northeast of Tokyo. Chains of giant waves up to 10 metres high swept across the adjacent shoreline of Japan around Sendai during the afternoon, producing widespread damage and an unknown loss of life.

This is shaping up to one of the worst natural disasters of modern times.

The tsunamis struck Hawaii overnight, producing only minor damage, but some 12 hours later reached the US west coastal area of Crescent City, near Oregon, where extensive damage resulted in the local harbour.

This event was probably as severe as the infamous Boxing Day tsunami that raced across the Indian Ocean on December 26 2004.

This Indian Ocean event was one of the worst ever natural disasters in recorded history, killing more than a quarter of a million people over eleven countries and this event in Japan is also a major tsunami disaster.

In September 2009 another deadly tsunami created devastation on a smaller scale around the Pacific Island nation of Samoa.

Once again the terrible phenomenon of a tsunami has captured the worlds headlines.

What is a tsunami?

Tsunami is a Japanese word meaning “harbour wave”. A tsunami is a wave or series of waves generated in the ocean by such phenomena as earthquakes, undersea land-slides, volcanic eruptions and meteor impacts. It should not be confused with ocean swell waves, which are generated by the action of wind on the surface of the sea, or tides, which are produced by gravitational effects of the Sun and Moon.

Undersea earthquakes, as we have just seen off the coast of Japan, are common around the so called Pacific Ring of Fire, a geologically unstable region that extends from New Zealand, across the Tongan region, Papua New Guinea, Indonesia and then northwards to Japan. It then travels east across the northern Pacific and moves down the west coast of both North and south America.

The Pacific Ring of Fire
(Image from Wikipedia Commons - click to enlarge)

This zone is largely generated by the movement of the Pacific tectonic plates against other adjacent plates. It has been unusually active this year, also producing the devastating earthquake across Christchurch.

Tsunamis are sometimes referred to as “tidal waves” or “seismic waves” but both of these terms are inaccurate descriptions.

Above - The Pacific tectonic plate runs close to Japan.
(Image from Wikipedia Commons - click to enlarge)

Tsunamis have produced tremendous devastation throughout history, causing massive damage along shorelines, wrecking many coastal townships and killing untold thousands of people through drowning.

The tsunami as a shallow water wave

When an earthquake occurs near or under the ocean, a tsunami can be generated, and the characteristics of this type of wave are markedly different to the “normal” waves we are used to seeing down at the beach. These waves may break on the shore say every 10 or 12 seconds (called the “wave period”), and have a distance of around 100 to 120 metres between wave crests (called the “wavelength”).

But tsunamis may have a period of up to an hour and a wavelength of around 100km, with the second and third waves still maintaining massive power. This wavelength is very much greater than the depth of the ocean through which the wave is travelling, which for the Pacific Ocean can be around 3000 to 4000 metres.

Waves with this characteristic are called shallow water waves, which is somewhat confusing because here we are talking about the deep ocean. But “shallow” in this case is only a relative term, meaning the ocean depth (~3000m) is shallow compared with the wavelength (~100km or 100, 000m)

It can be demonstrated through the physics of wave theory that shallow water waves move at a speed which is directly proportional to the depth of the water through which they are moving, and in a water depth of 3000 m, this translates to a wave velocity of ~ 170 m/s or over 600 kph. If a wave of this type is encountered by a ship at sea, it may be barely noticed, as the wave is spread out through the entire depth of the ocean and may only form a slight disturbance on the surface, although moving at great speed.

Another characteristic of shallow water waves is that they lose energy at a rate that is inversely proportional to the wavelength – meaning the longer the wavelength the further the wave can travel. The extremely long wavelengths of tsunamis means that they can travel extended distances, in the order of thousands of kilometers, or, in other words, across entire oceans.

Tsunamis approaching the shoreline

Whilst tsunamis are markedly different from ocean waves in all the ways described, the normal physics of wave motion still applies. All waves contain a certain amount of energy that is dependant on the mass of water being displaced (which is closely related to the height of the wave), and the velocity of the wave. This energy is largely conserved, apart from a slight dissipation over time.

A tsunami surging into shallow water
(Image from Wikipedia Commons - click to enlarge)

When the wave approaches a shoreline and the water becomes shallower, the wave begins to slow as a result of friction with the ocean bed. But the overall energy of the wave stays much the same, so to compensate for the slower speed, the height of the wave ramps up.

A tsunami approaching the shore will "arc up" sometimes to great heights
Image: Wikipedia Commons
(Click on image to enlarge)

This means that a tsunami, whilst barely noticeable at sea, quickly grows in height, and cases of waves reaching heights of 30 metres are known. An entire tsunami event may consist of several waves, called a wave train, each of which can carry a major destructive punch.

The final height and shape of the wave are largely determined by the topography of the ocean bed near the shoreline. As well as the celebrated wall of water towering over the beach as is often portrayed in the movies, the wave can also present as a rapidly rising tide moving a long way inland with unstoppable force, destroying everything in its path.

A tsunami train approaching shallow water will "bunch up" but increase in height. (Image from Wikipedia Commons - click to enlarge)

A sign that a tsunami is approaching is a lengthy retreat, or “drawdown” of the ocean along the shoreline, and the water level can retreat more than 300 metres seawards of its normal position when this happens.

Immense drawback of the ocean just before the onslaught of a tsunami wave at Kata Noi Beach, Thailand on December 26th 2004. Image: Wikipedia Commons. (Click on image to enlarge)

Destruction generated by tsunamis

Tsunamis can reach the coast with tremendous amounts of energy. They can create significant shoreline erosion, stripping beaches of sand that may have taken years to accumulate and uprooting trees and other coastal vegetation. Capable of inundating, or flooding, kilometers inland past the typical high-water level, the fast-moving water associated with the breaking tsunami can easily crush homes and disrupt coastal infrastructure such as powerlines and roadways.

As we have seen with the Japanese disaster, after crossing a built up area, tsunamis carry a massive volume of debris with them, and this acts as a colossal "grinder", scouring existing structures away, which then becomes part of the moving debris mountain.

A devastated town on the coast of Sumatra, seen just after the Boxing Day tsunami 2004, graphically illustrates the enormous power of a tsunami. Image: Wikipedia Commons. (Click on image to enlarge)

Tsunami prone areas and warning systems

Throughout history, tsunamis have been recorded in most of the oceans of the world. However because of inherently unstable geological conditions, the Pacific Ocean is particularly notorious, with frequent earthquakes occurring around the Pacific Rim.

No formal warning system was in place until 1960, when the devastation caused by a massive tsunami in Chile during May of that year led to the formation of the Pacific Tsunami Warning System (PTWS) located in Hawaii. This group organises and monitors a network of earthquake detectors and tide gauges which determine where earthquakes occur and whether or not a tsunami may have been generated.

After a major earthquake in Alaska in 1964, the PTWS concept was extended and the International Tsunami Warning System (ITWS) was created. Following the disastrous Boxing Day tsunami of 2004, this system was extended to cover the Indian Ocean.

As soon as an earthquake is detected, it is evaluated as to its location and intensity, and if it is thought that a tsunami may have been generated, calculations are made which estimate the speed of propagation of the wave, based on the depth of the ocean. Warnings are then issued to all countries in the affected area, and depending on the lead-time available, emergency preparations are begun.

The Japanese tsunami was particularly well photographed, including some unique footage of the wave trains approaching the shoreline taken from helicopter. This vision will be closely analysed by experts in an attempt to learn more about these massive and lethal monsters of the deep.

Extraordinary footage showing the tsunami slamming through the port of Kamaishi, in northeastern Japan can be seen here:

An untested hypothesis

An interesting hypothesis has been advanced to explain the "disaster clusters" we sometimes see - this year we have seen severe flooding in Australia, the massive Christchurch earthquake and the the Japanese tsunami - could these be connected in some way?

During times of strong El Ninos and La Ninas sea levels rise for prolonged periods over either the western or eastern sides of the tropical Pacific Ocean. Could this colossal extra weight of water be enough to disturb the Pacific plate and trigger periods of high seismic activity? The strong La Nina we've experienced this year has produced record flooding across much of eastern Australia but could it have also triggered the Christchurch and Japanese disasters?

This hypothesis is totally untested but it could help explain the confluence of natural disasters we sometimes see.


“Disasters, Events and Moments that Changed the World”, Richard Whitaker, New Holland Publishing, 2007

Sunday, September 27, 2009

Duststorms in Australia

Between Monday 21st and Saturday 26th September 2009 two very large dust storms swept across eastern Australia and affected three major cities – Canberra, Sydney and Brisbane. The dust cloud that covered Sydney on the morning of Wednesday 23rd was one of the most severe in recent memory, with visibility dropping below 100 metres in some areas, and thousands of tonnes of dust settling across the Sydney basin.

Dust storms are common over inland areas of NSW and Queensland, but usually they are prevented from reaching Sydney by the massive wall of the Great Dividing Range that acts as a large shield, preventing the dust from moving to the coastal fringe.

However when a strong cold front is involved, the dust can be lifted, up to 3000 metres above the ground, and swept over the mountains and across the coastal fringe.

Cold fronts can lift dust up to 3000 m
above the ground (Click on image to enlarge)

The front also tends to produce an organised line of dust that can extend hundreds of kilometres north and south, a line that rolls steadily eastwards and can be readily identified from satellite photography.

In these cases the dust consists of very fine particles of topsoil that are highly penetrative – even houses that have been carefully closed up will have their interiors carpeted with a fine film of dust.

Dust storm lining up with a cold front, 25th September 2009

On occasion the dust cloud can carry across the Tasman Sea and drop across New Zealand, producing red snow on the New Zealand Alps. Much of the dust also falls into the Tasman Sea and sediments at the bottom of the ocean in this area reveal evidence of many similar events that have taken place in the past.

The dust storm of 23rd September was over 1500 km long and 200 km wide (NASA picture)

Another severe dust storm affected Sydney during the summer of 1944 as the following newspaper article recalls.


SYDNEY, Sun 10th December 1944 – The Argus

Dense dust storms, accompanied by high temperatures, raged over most of New South Wales at the weekend. Bush fires in the Blue Mountains destroyed seven cottages, a dairy, a store, look- outs, and kiosks. Nineteen houses were destroyed in the Richmond district and four near Gosford.

A man and a woman aged 80 were burned to death in the fires. They were J. H. Barnes, who was burned in a paddock at Kurrajong, and . Miss Irene Cavanagh, who was trapped in a house at Oswald.

Some relief from the heat is forecast for tomorrow.

Sydney was swept by a violent westerly gale. The maximum wind velocity recorded at the Weather Bureau was 63 mph, but one gust at Richmond reached 76 mph.

The maximum temperature in Sydney today was 91deg, compared with 91.5deg yesterday. Clouds of dust carried by the wind from inland districts almost blotted out the sun at times.

Metropolitan fire brigades answered more than 150 calls. The task of extinguishing outbreaks was made more difficult by the gale.

One of the biggest dust storms to ever affect an Australian capital city occurred in February 1983, when a massive wall of dust swept across Melbourne, also carried along by a powerful cold front.

Friday, September 11, 2009

Thunderstruck! - The Lee Trevino Story

In 1975, Lee Trevino was at the height of his stellar professional golfing career. Born in 1939 into a poor family of Mexican origins, he had taught himself to play golf and after a 4 year term in the United States Marines, turned professional.

His self-taught golf swing was not in the classical style, but it had one big thing going for it - it worked! What seemed to be a series of unorthodox motions all self corrected by the point of impact, and 90% of the time he cracked the ball long and straight.

He hit the big time in 1968, when to everyone's amazement he defeated Jack Nicklaus to win the US Open. He never looked back after that and by 1975 he had won two US opens, two Open Championships and a PGA Championship, in addition to a host of smaller titles. He was recognised as one of the all time golfing greats, made all the more remarkable by the journey he made to get there.

Trevino was also likeable and friendly and was a particular favourite with the press gallery because of his humour and witty remarks. He once said

"I played the tour in 1967 and told jokes and nobody laughed. Then I won the Open the next year, told the same jokes, and everybody laughed like hell."

In 1975 he was playing in the Western Open, held that year at the Butler National Golf Club in Chicago, when he was struck by lightning. Miraculously he survived but his back was permanently injured and as he gradually worked his way back into the game, his swing was reduced and he was unable to practice as much as before.

Nevertheless he came back and won the Canadian Open in 1977 and 1979, and then amazingly the PGA Championship in 1984.

Largely as a result of the Western Open incident, a thunderstorm protocol was developed by the PGA, and today when storms are about during a tournament, meteorologists tracking them on radar advise the Tournament Director who can then postpone play and ask players to return to the clubhouse.

It is estimated that around 5% of people killed by lightning each year in the USA are struck on the golf course, and as a result safety in thunderstorms is actively promoted by the United States Golf Association (USGA).

So what is lightning?

A cumulonimbus, or thunderstorm cloud. Photograph from Wikipedia Commons. (Click on image to enlarge)

It is a massive electrical discharge that is generated by giant cumulonimbus clouds, which can also produce other types of severe weather such as hail, destructive wind gusts, heavy rain and even tornados. These clouds usually have an “anvil” shape and can tower up to 15 km in height - that is nearly twice as high as Mount Everest.

Lightning can discharge between cloud and ground, cloud and cloud as well as within two different areas within a single cloud. A lightning discharge can generate up to 1 billion volts of electricity and explosively heat up the surrounding air to nearly 10,000C or twice the temperature of the Sun’s surface.

The almost instantaneous heating of the air produces a shock wave in the air that travels outwards at the speed of sound and this is called thunder. The sound of thunder can travel considerable distances, depending on the existing atmospheric conditions but can often be heard out to 25 km from the lightning discharge.

A cloud to ground lightning strike
Photograph from Wikipedia Commons. (Click on image to enlarge)

The distance away that a lightning bolt occurs can be calculated approximately by counting in seconds from the moment the lightning is seen. The counting is then stopped after the thunder is heard and the resulting number of seconds then divided by 3. This will tell you approximately how far away the lightning discharged.

For example, suppose that 15 seconds elapse between the flash of the lightning and sound of the thunder. We divide 15 by 3 and obtain 5 and conclude therefore that the lightning bolt was about 5 km away. To convert to miles, we simply divide by 5 instead of 3 and in this case the lightning strike would have been around 3 miles away.

Lightning will often strike the tallest object in the area and on an open fairway this can, of course, be a human being. Trees are also struck often and can literally explode as the charge hits them. For this reason it is important to avoid sheltering under trees during a thunderstorm.

A tree torn apart by lightning
Photograph from Wikipedia Commons. (Click on image to enlarge)

The following tips are helpful for lightning safety on the golf course:

1. If there is an active thunderstorm about, return to the clubhouse or seek shelter in the nearest substantial building. The interior of a car, with the windows up, is also a safe shelter.

2. Stay clear of trees, metal structures and water, such as lakes and creeks that may be part of the course layout.

3. If caught in the open, crouch down in a squatting position and stay low. Avoid becoming the tallest object in the area.

4. Stay away from wire fences – these can conduct electric charge a considerable distance.

5. Before the game check the weather forecast so that you will be ready to act early.

Lee Trevino never lost his humour despite the ordeal. He was asked later about what he would do if he was caught on the golf course in a thunderstorm. He answered " I'd take out my one iron and point it to the sky because even God can't hit a one iron".

Lee Trevino was inducted into the World Golf Hall of Fame in 1981 and voted the 14th greatest golfer of all time by Golf Digest Magazine.

The world champion lightning strike survivor was not a golfer but a US Park Ranger named Roy Sullivan (1912 to 1983). He survived being struck by lightning on seven different occasions but later killed himself after a failed romance.

Reference: " All About the Weather", Richard Whitaker, New Holland Publishing, 2007

Thursday, September 3, 2009

Predicting the Weather - How far Ahead Can We Go?

Thou, nature, art my goddess; to thy law
My services are bound.
King Lear – William Shakespeare

Computer models have been of tremendous assistance in weather prediction. But the accuracy of these models is heavily dependant on how well we can define the current state of the atmosphere, because this forms the foundations of any attempt to predict the future.

We tend to think that predicting the future using mathematics is such a complicated procedure that only scientists can understand the process but most of us have probably engaged in such predictions, perhaps without realising it at the time.

We look at a simple example that we reviewed in a previous post, but this time from a different angle. Let’s say we’re in a car moving down a freeway at 100 kph. We want to know where the car will be after 2 hours. Obviously the answer is 200 km away but let’s step back and see how be arrived with this solution.

We have, perhaps unknowingly, used a mathematical formula


which in words says “distance travelled equals speed multiplied by time”.

In this case S = 100 and T=2, so to obtain our answer we use the process of multiplication.

So D = 100x2, giving us our answer of 200 km.

We have therefore been able to predict the future position of our car by knowing

(1) The intitial conditions – the car is travelling at 100 kph
(2) A mathematical equation that describes the motion - D=SxT
(3) A method of “solving” the equation – in this case the process of multiplication.

Now, lets say the cruise control on our vehicle is slightly faulty and varies between 98 kph and 102 kph – where will our car now be after two hours?

Without precise knowledge of how the cruise control is varying – another equation is required for this – we don’t really know. But what we can say, using the upper and lower speeds, is that the car will be between 196 and 204 km down the road. And after 4 hours this band of uncertainty will double in size.

The same situation exists in numerical weather prediction. The current state of the atmosphere – involving the global distribution of temperature, pressure, wind humidity and other variables, both at the surface and in the upper layers of the atmosphere at a given moment form what we call the “initial conditions”, that are the starting point for all future predictions.
These are fed into the computer as an “Analysis” and are then processed via a “Prognosis scheme”, using mathematical equations. This produces a forecast, which is then fed back into the system as new initial conditions and the process is repeated until we reach the desired forecast interval.

Schematic of the numerical weather prediction process

If we could produce perfect initial conditions the computer could theoretically produce perfect forecasts. But to do this we would have to know where every molecule of air is at any one moment, and what direction and speed they are all moving.

Clearly this will never be possible and this imposes an upper limit on how far ahead we can usefully forecast the weather. Just as with our car example, the errors we begin with in our initial conditions tend to magnify with time, producing a decrease in forecast accuracy the further ahead we try to go.

Another interesting feature of the atmosphere is that it appears to move through modes of “high” and “low” predictability – times where the weather patterns are persistent and predictable and others where atmospheric motion is volatile with a high degree of unpredictability.

This can be demonstrated by the use of multiple computer runs, each with slightly different initial conditions. On some occasions a small difference in these conditions will only produce a slight change in the forecasts, out to say 4 days ahead. At other times, starting with only slightly different initial conditions vastly different outcomes rapidly evolve, indicating a state of high unpredictability in the atmosphere at that time.

A simple example of predictable and unpredictable systems involves dropping a group of table tennis balls on a hollow cardboard cone. If the cone is inverted, the balls will end up in the bottom even if we drop them from slightly different positions, providing, of course, we remain within the radius of the base of the cone.

However if the cone is standing, rather than inverted, even a small difference in position from where we drop the balls will produce a large difference in outcome – that is where they come to rest. The first system is highly predictable whereas the second is not.

Predictable and unpredictable systems

Weather prediction can be considered as a process in which a field of cones is negotiated, some standing and others inverted, producing areas of high and low predictability.

Taking all these factors into account it is the general consensus amongst meteorologists that meaningful weather forecasts showing real skill will eventually be achievable out to about 2 weeks ahead. After that the inherent unpredictability of the atmosphere will probably form a “glass ceiling”, impenetrable to even the most extensive observational network and the largest computers.

Reference: "Understanding Climate Change", Richard Whitaker, New Holland Publishers, 2008