Crisis---Format of print

Crisis

Introduction--Crisis

Water has been both worshipped and feared: it is essential for life, but causes natural disasters through floods and storms. In ancient times, water was seen as one of the four elements which, along with fire air and earth, formed the building blocks for all things on Earth. Over two thirds of the Earth's surface is covered with water. Most of it is sea and ocean, which are home to a wide variety of animals. Less than one per cent is the fresh water needed of drinking and growing crops. Yet, water can be a destructive power. Millions of people around the world suffer from monsoon rains, river floods, tropical storms and raging seas. Such dangers have forced people to divert and hold back water, by building dams, dike and flood barriers. But when its full force is unleashed, nothing can stop this raging element. Cities are at the greatest risk from floods, as their paved streets prevent water from draining away. In major disasters, the emergency services are stretched to the full. They use boats, and also helicopters to rescue people from the tops of buildings, and to throw ropes for people to cling to.

Pollution

The nature of effluents

Water pollution is most commonly associated with discharge of effluents from sewers as sewage treatment plants, drains and factories. Outfalls of this kind are known as 'point-source discharges'. Most cases of accidental, negligent or illegal discharge are also from point sources. The concentration of pollutant in the receiving water is initially high decreasing as the distance from the point of discharge increases. The effects of the pollution are therefore frequently easy to observe. Some of the more serious forms pollution arise, however, from 'diffuse' sources, that is the pollutant does not enter the water from a single point. For example, in agricultural areas, surface water runoff and groundwater infiltration onto lakes and rivers can introduce plant nutrients (from fertilisers) and pesticides in substantial quantities to water bodies. The effects of pollution from diffuse sources can be serious, but are often less immediately obvious than those from point sources as there is no adjacent unpolluted area with which comparisons may be made. Many pollutants also enter water through fallout from the atmosphere. Historically, control and prevention of water pollution have concentrated on point sources as these are more obvious, easily identifiable and in theory easier to regulate at the point of origin. As awareness has increased of the significance of diffuse sources of pollution, control strategies have been under development but are based more on the application of good practices designed to reduce pollutant impact rather then on regulation of specific sources of input.

Most effluents are complex mixtures of a large number of different harmful agents. These include toxic substances of many kinds, extreme levels of suspended solids, and dissolved and particulate putrescible organic matter. In addition, many effluents are hot, of extreme pH value, and normally contain high levels of dissolved salts.

Most effluents also vary in their strength and composition, on a seasonal diurnal or even hourly basis. Most sewage treatment plants report regular diurnal peaks and thoughts in their output according to patterns of water use. Sometimes storm-water drains are connected to the sewerage system, so the strength of the sewage effluent will vary with rainfall. Alterations in the strength and composition of sewage also influence the efficiency of the sewage treatment process, so that dilution of the influent does not necessarily cause an improvement in the quality of the effluent. In industrial plants, variations in the quality of the raw materials, or changes in specification of the finished product, will require changes in the operating conditions of the plant and lead to changes in the composition of the effluent. Many industrial processes are 'batch' rather than continuous processes, so that some effluent discharges will be intermittent rather than continuous.

Organic pollution

The discharge of excessive quantities of organic matter is undoubtedly the oldest, and even today the most widespread form of water pollution.

The major sources of organic pollution are sewage and domestic waste; agriculture (especially runoff from inadequately stored animal waste and silage); various forms of food processing and manufacture; and numerous industries involving the processing of natural materials such as textile and paper manufacture. Most organic waste waters contain a high proportion of suspended matter, and in part their effects on the receiving water are similar to those of other forms of suspended solid. However, the most important consequences of organic pollution can be traced to its effect on the dissolved oxygen concentration in the water and sediments. In unpolluted water, the relatively small amount of dead organic matter is readily assimilated by the fauna and flora. Some is consumed by detritivorous animals and incorporated into their biomass. The remainder is decomposed by bacteria and fungi, which are themselves consumed by organisms at higher trophic levels. The activity of microorganisms results in the breakdown of complex organic molecules to simple, inorganic substances, such as phosphate and nitrate, carbon dioxide and water. During these metabolic processes, oxygen is consumed. However, where the organic load is light, the oxygen removed from the water is readily replaced by photosynthesis and be re-aeration from the atmosphere.

Where the input of organic material exceeds the capacity of the system tm assimilate it, a number of changes take place. How far the sequence of changes proceeds depends upon the severity of the organic load and the physical characteristics of the receiving water. Initially, the enhanced level of organic matter will stimulate increased activity of the aerobic decomposer organisms. When their rate of oxygen consumption exceeds the rate of re-aeration of the water, the dissolved oxygen concentration in the water will fall. This alone may be sufficient, as argued earlier, to eliminate some species, which may or may not be replaced by others with less rigorous demands for oxygen. If the drop in oxygen concentration is very severe, the aerobic decomposers themselves will no longer be able to function, and anaerobic organisms will become predominant.

Ammonia, cyanides and phenols

Ammonia, cyanides and phenols are considered together because, with copper and zinc, they are the most widespread and serious toxic water pollutants in industrialised countries. Ammonia and its compounds are ubiquitous constituents of industrial effluents because ammonia is a staple raw material in many branches of the chemical industry; it is, therefore, a common end-product of industrial processes as well as an important by-product of others, notably the production of coke and gas from coal, from power generation and from most processes involving- the heating or combustion of fuel. It is also a natural product of the metabolism of organic wastes in treatment plants and receiving waters. The toxicity of ammonia to fish is well documented, and although less is known of its effect on invertebrates it appears that levels of ammonia which are tolerable to fish present little danger to most invertebrates. In aqueous solution, ammonia forms an equilibrium between unionised ammonia, ammonium ion and hydroxide ions:

NH3 + H2O = NH4+ + OH-

Unionised ammonia is very toxic to most organisms, but ammonium ion is only moderately toxic. The toxicity of the solution therefore depends on the quantity of unionised ammonia. This in turn depends upon the pH and temperature of the water as pH and temperature rise, the proportion of unionised ammonia also rises. The effect of pH and temperature on ammonia toxicity is therefore considerable. In order to know whether a given level of total ammonia is likely to be toxic, it is necessary to use the pH and temperature values to calculate the corresponding level of free ammonia. As an example, the European Inland Fisheries Advisory Commission (EIFAC) recommends that unionised ammonia concentrations should not exceed 0.025 mg1-1. In a water of pH 8.5 at a temperature of 20° C, this corresponds to a total ammonia concentration of 0.22 mg1-1. In a cooler, acid water, however (pH 6.5, 5° C), a concentration of total ammonia of 63.3 mg1-1 would be acceptable, whereas at pH6.5 and 20'C, the maximum acceptable concentration of total ammonia would be 20 mg1-1.

KCN + H2O = H+ + K+ + HCN = CN- + H+

The dissociation, and consequently the toxicity of cyanide, is pH-dependent, low pH favouring the formation of undissociated HCN which is highly toxic.

Pesticides

Pesticides are a diverse group of poisons of widely-varying chemical affinities, ranging from simple inorganic substances to complex organic molecules. Of the latter, some are natural metabolites, particularly of plants, while others are synthetic derivatives of natural products or completely synthetic substances produced in chemical factories under conditions which do not exist in the natural world. They live in common only that each pesticide is highly toxic to some forms of life and of intermediate or negligible toxicity to others, and that they have been widely introduced into the natural environment. Pesticides are introduced into aquatic systems by various means: incidentally in the course of their manufacture, and through discharge consequent upon their use. Surface water runoff from agricultural land and the side-effects of aerial spraying are especially important, and many serious pollution incidents arises through the accidental or negligent discharge of concentrated pesticide solutions which have been used for agricultural purposes such as sheepdipping. Additionally, many pesticides are deliberately introduced into bodies to kill undesirable organisms such as insect or molluscan vectors of human diseases, weeds, fish and algae.

Pesticides ire also used in many industrial processes, for example in the manufacture of textiles and in the production and processing of perishable materials such as paper and timber products. They are therefore an important component of many industrial effluents. In many countries, the special significance of pesticides as pollutants (and as widely used toxic chemicals in the working environment) has led to the development of strict controls on their use.

Insofar is it is possible to generalise about the polluting effects of such a diverse (group of substances, the following points are perhaps of greatest significance. First, effective pesticides are more or less selective in their effects, that is they are extremely toxic to some forms of life and relatively harmless to others. Second, their modes of application vary according to the circumstances. In some cases, pesticides are applied in relatively high concentrations for relatively short periods. This pattern of application typically occurs where pesticides are applied to water to kill weeds, disease vectors or other undesirable organisms, or as an incidental effect of aerial spraying of crops. Here, the principal concern may be to determine their short-term toxicity to non-target organisms, and it may be advantageous to devise specific toxicity testing protocols in order to estimate the impact of the pesticides on the receiving-water biota. However, in lowland rivers draining agricultural areas, pesticides arc more likely to be present at low but fairly consistent levels, and in this case the major areas of toxicological interest will be their potential sublethal effects, their capacity to accumulate in individual organisms and via the food chain, and the development of resistance through acclimation and/or genetic adaptation. Many pesticides arc known to be refractory to chemical and biological degradation and their persistence in the environment has for many years been a cause for concern.

Detergents

Synthetic detergents are in interesting group of pollutants because they were virtually unknown before 1945, yet within a few years became responsible some spectacular water pollution which, usually, came rapidly to the attention of the general public. The alkylbenzene sulphonate detergents rapidly replaced soap is domestic and industrial cleaning agents because of their cheapness and greater efficiency, and particularly because they did not cause precipitation of calcium salts in areas supplied with hard water. unfortunately they were not readily broken down by sewage treatment processes, giving rise to problems of toxicity to the receiving-water biota, and of foaming in watercourses and treatment works.

In areas where industrial usage of detergents was pronounced (for example, in textile-processing Industries) whole towns were frequently covered in detergent foam; in waste treatment works, a number of serious accidents occurred through, for example, operatives falling into sedimentation tanks which were concealed under a thick layer of foam. Consultation between regulatory authorities and the detergent manufacturers led to research which showed that modifications to the manufacturing process could produce linear alkylbenzene sulphonate (LAS) detergents, which were rapidly degraded in conventional waste treatment plants. From 1965 onwards, 'soft' or biodegradable detergents were introduced for domestic use, and although these ire generally more toxic to aquatic organisms, their unbranched Hydrocarbon chain is more readily broken down in treatment processes and in practice, toxicity and foaming problems had largely disappeared by the early 1970s. Synthetic detergents remain significant causes of pollution in some circumstances however. 'Soft' detergents are not suitable for use in certain industrial processes. Detergents are widely used as components of oil-dispersants, particularly in coastal and marine habitats, and are often more toxic to aquatic organisms than the oil itself. Finally, some components of detergent formulations exert adverse effects of their own. The best known example is the high level of phosphate found in many formulations. Less widely appreciated are the adverse effects of boron, from perborate additives to detergent formulations, which can cause adverse effects on crops if contaminated surface waters are used for irrigation.

Oil and Petroleum Products

Oil pollution is commonly perceived as being a problem associated mainly with the marine environment, but in fact oil and related substances account for about one-quarter of reported pollution incidents of fresh waters in Britain; and probably the pattern is not much different in other parts of the world. Also, about one-quarter of all the oil released to the seas by human activity is estimated to enter via rivers. The sources of oil pollution are the usual ones - illegal, negligent or accidental discharges, plant failures and so on - but to these must be added inputs from roads and railways, particularly in the case of traffic accidents, and discharges associated with oil extraction from inland oilfields and processing plants.

The effects of oil discharges vary enormously, because the characteristics of the receiving waters and the various types of oil are themselves very variable. Fortunately many small discharges have relatively trivial effects, but substantial discharges can have severe impacts. Generally, light oils are relatively volatile and disperse quickly, though they are extremely toxic and can cause severe local damage. Fast-flowing waters often recover rapidly, over a few weeks or months, but lentic waters are much more susceptible to long-term damage. Heavy oils are less toxic, but can have marked physical effects in the substratum and the banksides, which of course will be reflected in changes to the biological community. Heavy oils may remain in situ for long periods; they do, over time, decompose biologically and chemically, but in so doing impose a high BOD. Frequently, the effects of oil pollution are not dissimilar from those of heavy organic pollution, with varying levels of toxic effects adding to the overall impact. Oils, unlike most forms of water pollution, can also have damaging effects on terrestrial organisms, such as plants, birds and mammals living at the water's edge, since heavy oil contamination usually lead,, to deposition of oil on the banks of likes or rivers.

Generally, the use of oil dispersants, which are commonly used in dealing with marine spills, is avoided in freshwater because of their high toxicity. Also, the physical conditions of freshwater habitats are often amenable to containment and recovery of oil by booms, skimmers and/or tile use of absorbent materials.

Agricultural Water Supply

Agricultural activities are a major source of serious water pollution, but at the same time agriculture imposes a heavy demand for supplies of clean water. The seriousness of such problems depends, to a large extent, on the varying conditions which prevail in different parts of the world, especially in relation to the climate, the availability of water and the extent to which waste treatment facilities and general public health provisions are established. The disposal of waste waters, whether treated or not, and of sludges from treatment processes to agricultural land has many economic and agricultural benefit, but there are a number of hazards associated with these practices. Even where the deliberate reuse of water is not practiced, it is increasingly likely that agricultural water supplies will be drawn from water bodies which have previously received waste matter.

The most obvious adverse effects of polluted water in agriculture relate to he presence of toxic matter, especially heavy metals, and of pathogenic organisms. Agricultural animals probably do not differ much from humans in their sensitivity to toxic heavy metals, and heavily-contaminated water is no more acceptable to them than it would be as a potable supply for humans. The sensitivity of plant species to heavy metals in their environment is well known. Although there is some possibility that crops may accumulate sufficient heavy metal to be hazardous to consumers, in practice the effects of toxic metals are initially economic; some crops will give a reduced yield, or fail altogether, if the levels of toxic metals in the soil or irrigation water are too high. Thus water pollution can restrict the uses to which land can usefully be put, or impose extra costs relating to the supply of water of adequate quality. Boron, for example, is like many other elements an essential requirement in trace amounts for plants; in excess, however, it is toxic. The widespread use of perborates in detergent formulation has led to concern that domestic sewage effluent, without any contamination from industrial sources, could so elevate the boron content of receiving waters as to exert an adverse effect on crops. Consequently it has been necessary for national and international agricultural agencies to formulate detailed recommendations concerning the chemical quality of water used for various agricultural purposes.

Pathogenic organisms in water or sludges applied to agricultural land present obvious potential dangers. Again, the magnitude of the hazard depends greatly upon the eliminatic, agricultural and general public health situation of the geographical area concerned. Infective life stages of parasites can be ingested by animals contaminated water and transmitted directly to human consumers, particularly from salad vegetables or other crops which are eaten uncooked. Also, microbial contamination of arable crops through irrigation with contaminated water can contribute to the spread of disease.

Industrial Water Supply

Industrial usage accounts for a very large proportion of the total demand for water, and about two-thirds of the water used in industrial processes is used for cooling. The use in some industrial processes of sewage or other effluents, or of water which is too polluted for other water supply purpose, would appear to offer some advantages. In practice, the use of polluted water in industrial processes is subject to certain constraints. For example, the diary and food-processing industries obviously require water of the highest quality, and it is not always economically feasible to construct and operate safely water distribution systems in which water of different quality is supplied to different factories within an area.

Many of the problems which can arise are not of a strictly biological nature; for example, the presence of ammonia and other chemicals can exacerbate corrosion problems in pipework. A common difficulty is the growth of bacterial slimes and the accumulation of organic detritus in cooling systems; this can be controlled by chlorination, provided that the presence of free chlorine at relatively high levels does not interfere with the normal operation of the factory. A new and recent pressure is the demand from some very modern industries, such as the manufacture of electronic components, for water of a very high standard of purity. This could lead to the siting of manufacturing plants, often dealing with highly toxic chemicals, in the vincinity of the least-polluted water bodies of greatest utility and conservation value. In many countries planning considerations prevent this, and the alternative approach is to require potable water of the highest quality, and then to subject it to even further advanced treatment at the point of use.

Natural Disaster

Droughts

"El Nino is continuing to evolve. Continuing to be a very awesome event." Nick Green, Oceanologist, 1997

Too little water can be as disastrous as too much. A lack of water is called a drought. In times of drought, people and animals die of thirst and crops wither, causing famines that can kill millions of people even in areas far away from the affected region. Wars and deforestation can make droughts worse - without trees, the soil cannot retain nearly as much moisture.

In 1997, a weather phenomenon began brewing in the Pacific Ocean. Called "El Nino", it is a warming of the equatorial Pacific off South America which causes unusual changes in the climate around the world. This may well be the largest climatic event of the century, responsible for violent weather and droughts in Brazil, Africa, Australia and even the United States. In Indonesia, where the weather had been unusually dry, the farmers and logging companies continued to clear forests by burning trees, setting fire to large parts of the country. The El Nino in 1993 to 1994 was not severe but, the one in August 1983, caused global damage estimated at £17 billion. High winds and heavy rains in the Arizona desert in the United States turned streets in to rivers and toppled power lines.

Dam-busters

"The gates slowly opened, and an enormous wall of water came towards us." Eye-witness, Florence, Italy, 1966

Dams hold back such vast amounts of water that a failure can cause terrible floods. Failure usually results from neglect, poor design, or earthquake damage. When a dam bursts, an overpowering surge of water is released downstream which destroys everything in its path.

At exactly 7:26 a.m. on 4 November 1966, every electric clock in the city of Florence in Italy stopped. There was no power for the next 24 hours, and all communication with the outside world was served. The worst storms in Italy for 1,000 years had caused the river Arno in Florence to flood.

The operators of a hydroelectric dam 46 km (29 miles) upstream should have gradually released rainwater as it built up. Instead they waited until the strain on the dam gates was so immense that they were forced to open them at once. Within minutes, the city was under 2 m (6 ft) of water. The ancient sewer system broke up and waste was forced out of manholes all over the city. Helicopters were drafted in to airlift survivors from rooftop, and rescue workers were brought in from other countries to assist. The extent of the disaster caused 5,000 people to lose their homes and inflicted servere damage on many of Florence's priceless works of art.

Deep waters

"Delivered from gravity, I flew around in space¡K" Jacques Cousteau, diver

Deep waters are among the most dangerous places in the world. There is little or no light and the pressure from the water is too great for the human body to stand - an unprotected diver would be crushed.

Diving suits, such as the NEWTSUIT, allow people to explore the depths, and are also used in rescue situations. In emergencies, a range of special rescue vessels is used. Submersibles are mini-submarines which can transfer emergency supplies to the crews of damaged submarines, and can rescue crew members if necessary. "Hyperbaric chambers" bring injured deep-sea divers to the surface at a steady pressure: if they ascend too quickly, they can suffer from a potentially fatal illness called "the bends".

Fatal tides

"After 12 freezing hours stranded at the sea, the sight of the lifeboat was like a miracle." Survivor of shipwreck, North Sea, 1988

In Britain alone coastguard services receive about 5,000 calls a year. Coastguard monitor shipping activity and are usually the first to call out naval or air rescue services. A usual lifeboat crew consists of between five and seven people whereas inflatable lifeboats are crewed by just to or three. Around 1,500 lives are saved every year by volunteer lifeboat crews. Many distress calls come from people caught unawares by an incoming tide or by an incoming tide or by waves which suddenly crash on to the shore, leaving them cut off and stranded on rocks or in a bay. Some of the stranded attempt to swim to shore which can end in disaster as strong tidal currents can carry a person becomes cold and wet, there is a risk of hypothermia - a potentially fatal condition in which the body temperature drops well below normal. Often, the first task of a rescuer is to wrap the survivor in warm blankets to help raise the body temperature. With the growing popularity of watersports, the number of emergency call-outs increases. In open seas, currents can wash small boats way off course. Here, US coastguards rescue a group of refugees from Haiti, whose boat had been washed off course.

Floods

"I will bring a flood of waters upon the earth: everything that is on the land shall die." God's word's in the Bible

Over just a few days, relentless rain can submerge whole towns. "Flash floods" are even more terrifying because of the speed at which they happen. In storms, torrential rain can flood normally calm rivers in under 30 minutes. This is not surprising when a raindrop can measure 1 cm (1/2 in) in diameter and a hailstone up to 10 cm (3in) in diameter!

Water is heavy and, when it is moving at great speed, it becomes a battering ram that can sweep whole houses along in its path. Cars can also become death traps. Witnesses report hearing screams for help above the roar of flood waters, but are often powerless to help victims trapped areas, people often use boats or rafts to get away from their homes.

The battle against flooding is fought by building effective barriers and by forecasting floods before they happen so the area can be evacuated. But, emergency warnings often come too late, or people refuse to abandon their homes. Floods don't just cause drowning. Mud and broken sewage pipes contaminate drinking water, causing disease to spread and, without aid, many people starve.

Monsoons

"The monsoon rains bring a relief from the hear, but can cause massive devastation." Shopkeeper, India, 1997

Every June in India, the monsoon comes, bringing rain for three months, and sometimes it is torrential. The flooding can be terrifying. Rivers burst their banks, power failures cause shops to close, and streets are turned in to muddy waist-high rivers. Many people suffer injuries from stepping on glass and other objects submerged in the water and there is a high risk from water-borne disease. Yet, wherever possible, life goes on: Indians have got used to the monsoons. They build dams and huts with raised floors, and store food on high platforms. The floods bring boatman, ready to carry people from door to door for a fee. In some years these torrential rains turn into disaster. In these cases, the army and relief organizations try desperately to distribute food and medical supplies. But, such is the scale of monsoon floods in India and Bangladesh, that often they struggle to provide sufficient help and it can take weeks before the situation is brought under control.

River floods

"The surging water annihilated everything in its path." Description of Big Thompson flood, 1976

In 1976, an enormous storm dropped around 25 cm (10 in) of rain onto the Big Thompson River in Colorado, United States, in as little as four hours. The flood waters rushed down the river canyon, sweeping away roads, cars, trees and even a power station. The torrent broke up the road surface, sending huge chunks up into the air. It was difficult for the emergency services to get close enough to help people and at least one ambulance was knocked off the road by the water. Helicopters were brought in to pick up the survivors. It took months for the army to clear all the wreckage using large tractors.

River floods are the most dangerous in canyons or down mountains. The extra water hurtles along until it hits open land which is where people often live.

Rough seas

"Some waves are just too big for a small ship, even with the most experienced sailors. " Yachtsman at Cape Horn

Since people first took to the open seas, they have risked disaster from high waves and winds, fog, hidden rocks and reefs, and other ships. One of the most treacherous journeys is that around Cape Horn. This most southern point of South America juts out into Drake Passage - a narrow sea connecting the Atlantic and Pacific oceans. Fierce storms are common and the sea is always cold. The Dutch sailor, Willem Cornelis Schouten, was the first to sail around the Cape in 1616. In the great days of sailing, this journey was an all-important link between the Pacific and the Atlantic, and hundreds of ships were wrecked attempting it. Today, the lighthouse at Cape Horn marks a largely uninhabited area, and plays a crucial role.

One of the first lighthouses was built in 280 BC at Alexandria in Egypt, to guide sailors journeying across the Mediterranean Sea. Lighthouses have been used ever since to guide ships in storms and to help the crew avoid hidden rocks. Sometimes people called wreckers used to light beacons on cliff tops. Thinking that they were lighthouses, sailors would take the wrong course and crash against the rocks, leaving the cargo to be looted by the wreckers. Today's lighthouses are equipped with foghorns and radio beacons to help ships navigate safely in all weathers.

Tropical storms

"The people of Acapulco were not used to getting hurricanes and didn't know what to expect." Red Cross Official, 1997

A severe tropical storm - called a hurricane, cyclone, or typhoon, depending on where it occurs - is a roaring vortex of wind which moves across the sea at speeds of up to 360 km/h (220 mph). The winds are so strong that anything in their path risks being destroyed.

In October 1997, Hurricane Pauline hit the holiday resort of Acapulco, Mexico - a town unused to hurricanes, in some areas, 50 cm (20 in) of rain fell in less than 24 hours, causing massive flooding and mudslides. More than 400 people were killed. Relief workers struggled to reach the mountainous and remote areas which had felt force of the hurricane. Food, temporary housing and even 20,000 comfort kits (including toothpaste and brushes) were rushed in, and the clean-up operation was immense. For weeks, people wore paper face masks to protect against clouds of brown dust caused by the dried mud scraped up among the debris.

Tsunamis

"The wave, like an enormous hand crumpling a long sheet of paper, crushed the houses one by one." Eye-witness, tsunami in Chile, 1960

In 1960, an earthquake in Chile started a tsunami that swept across the Pacific to Japan. Huge waves washed over many coastal towns, destroying 50,000 houses and killing hundreds of people.

Tsunamis are huge waves up to 30 m (100 ft) tall which are set off by underwater volcanoes or earthquakes. Scientists use earthquake-monitoring devices called seismographs to predict when a tsunami will hit a particular coast.

The waves can travel at 800 km (480 miles) per hour and are devastating when they reach shallow water. They crash onto the land, washing people, animals, homes and cars away - no sea wall is high enough to stop them. The power of tsunamis is so great that, in 1692, one that hit Port Royal in Jamaica threw ships onto the tops of buildings. It is said to have moved mountains and created huge splits in the earth which swallowed people whole.

Weird water

"It was a terrible dark elephant grey, of a loathsome texture." First sighting of the Loch Ness monster, 1933

For centuries, the power of water has been a source of fascination and so it is no surprise to find countless stories and legends about this vital element.

For most of us, the oceans are as much of a mystery today as they were to the ancient sailors who told stories of sea gods and monsters to explain storms and shipwrecks. Even now, we are still excited by reported sighting of the Loch Ness monster. Perhaps one of the most enduring legends is that the city of Atlantis whose ruins are believed to lie in the ocean's depths since being engulfed by waves in ancient times. There is no proof that Atlantis ever existed, yet searches for it continue.

From swirling whirlpools to the hot, bubbling waters of geysers, people have always been intrigued by weird and wonderful watery phenomena. But water is also claimed to have great healing power. Many ill people visit the holy spring at Lourdes in France, where the water is believed to heal the incurable.

Frozen waters

"The decks broke up, the great beams snapping with a noise like gunfire." Ernest Shackletion, Antarctica, 1914

The freezing waters around Antarctica can be treacherous. In summer, the seas are dotted with large chunks of floating ice and, in winter, the water's surface freezes into one continuous sheet of ice.

Here, one of the most incredible real-life adventures took place. In 1914, Irish explorer Ernest Shackleton was sailing through the Weddell Sea, a large gulf that cuts inot mainland Antarctica. Without warning, huge sheets of ice crushed his ship, samashing its beams like matchsticks. The 28-strong crew were forced to abandon ship and set up camp on the drifting ice, but gale-force winds soon ripped their tents to shreds. Existing on penguin meat and seaweed, food supplies soon became scarce and Shackleton was forced to lead his crew on an extraordinary trek over frozen seas to Eleplant Island, a tiny land mass about 1,000 km (620 miles) below South America. Leaving some men there, he continued with five others to South Georgia Island where, after a jounery of almost 2,880 km (1,800 miles), he finally reached a whaling station. The station's commander who had seen them off two years before, now no longer recognised them as they looked so wild. All 28 crew were rescued.