IELTS Academic Reading Practice Test 9

In the first half of the nineteenth century London was the largest city in the world, and its population was growing rapidly, from about one million in 1801 to roughly two and a half million by 1851. Its arrangements for dealing with human waste had not kept pace. Many households relied on cesspits, which were emptied irregularly and often overflowed. Ironically, the spread of the flushing toilet made matters worse. From the late 1840s, householders were encouraged to connect their drains to the existing sewers, which had been designed to carry rainwater and which emptied directly into the River Thames. The river, from which many Londoners still drew their drinking water, became an open sewer.

The consequences were deadly. London suffered major outbreaks of cholera in 1832, 1848–49 and 1853–54, each of which killed thousands of people. Most doctors at the time believed that the disease was spread by miasma, a poisonous vapour thought to rise from decaying matter. In 1854 the physician John Snow showed that cases in one district of Soho were clustered around a single public water pump, and argued that cholera was carried in contaminated water. His explanation, however, was not widely accepted during his lifetime.

The crisis that finally forced action was not a disease but a smell. In the unusually hot summer of 1858, the stench from the Thames became so overpowering that the episode became known as the Great Stink. The newly rebuilt Houses of Parliament stood on the riverbank, and curtains soaked in chemicals were hung at the windows in an attempt to make the building usable. Within weeks, Parliament passed legislation giving the Metropolitan Board of Works, a body created three years earlier, the authority and the funds to build a new system. The task fell to its chief engineer, Joseph Bazalgette.

Bazalgette's solution was based on interception. London's existing sewers and buried rivers generally flowed from the higher ground to the north and south down towards the Thames. Rather than replacing them, he proposed to build large new sewers running roughly parallel to the river, from west to east, which would intercept their flow before it reached the Thames. Three intercepting sewers were built on the north side of the river, at high, middle and low levels, and two on the south side. Wherever possible the sewage moved by gravity, as the sewers fell gently towards the east. In total, the scheme comprised about 82 miles of main intercepting sewers, fed by some 1,100 miles of smaller street sewers.

Gravity alone could not do all the work, since the low-level sewers lay too deep to discharge naturally. At pumping stations, notably Crossness on the south bank and Abbey Mills on the north, enormous steam-driven beam engines lifted the sewage into higher channels. These buildings were designed with remarkable architectural ambition: Crossness, opened by the Prince of Wales in 1865, contains richly decorated ironwork, and Abbey Mills is often nicknamed a cathedral of sewage.

The sewage was then carried to outfalls at Beckton and Crossness, well downstream of the city centre. There it was held in large reservoirs and released into the river on the ebb tide, so that the current would carry it out towards the sea. The reservoir at Crossness alone could hold about 27 million gallons.

On the north bank, the low-level sewer was built into the new Victoria Embankment, a wide strip of land reclaimed from the river between Westminster and Blackfriars. The embankment also contained an underground railway and pipes for gas and water, and on its surface a new road and gardens were laid out. Construction of the whole network required around 318 million bricks. Bazalgette also insisted on using Portland cement, a relatively new material that was stronger than traditional mortar and set hard even under water, and he imposed strict testing of the batches delivered to his sites.

One of Bazalgette's most celebrated decisions was to make the sewers considerably larger than the population of the time required. Having calculated the volume of waste that each person would produce, he increased the dimensions generously to allow for future growth and unforeseen demands. This generosity is one reason why a system designed in the 1850s continued to serve a much larger city for well over a century. The health benefits were also striking. When cholera returned in 1866, most deaths occurred in a part of East London that had not yet been connected to the new system, and that outbreak proved to be the city's last major epidemic of the disease.

The Victorian sewers are still in use, but because they carry both sewage and rainwater, during heavy storms they overflow into the Thames through outlets intended as safety valves. As London grew and more of its surface was covered by roads and buildings, such overflows became increasingly frequent. To deal with the problem, a 25-kilometre tunnel running largely beneath the river, known as the Thames Tideway Tunnel, was constructed to capture the overflow and carry it away for treatment. Building it took almost a decade, and much of the work was carried out by large tunnel-boring machines working deep beneath the riverbed. It became fully operational in 2025, a modern extension of the system that Bazalgette began more than 150 years earlier.

Around 1,350 volcanoes on land are regarded as potentially active, and in a typical year several dozen of them erupt. Roughly 800 million people live within 100 kilometres of one. Predicting the precise moment of an eruption remains beyond the reach of science, but volcanologists can often detect the signs that a volcano is becoming restless and estimate how likely an eruption is over the coming days or weeks. Most eruptions are preceded by some form of unrest, although this may last for anything from a few hours to several years. They prefer to speak of forecasting rather than prediction, in much the same way as meteorologists do, and their forecasts depend on the patient collection of several different kinds of evidence.

Systematic monitoring has a surprisingly long history. The world's first volcano observatory was founded on the slopes of Vesuvius, near Naples, in 1841. In 1912 the geologist Thomas Jaggar established the Hawaiian Volcano Observatory on the rim of Kīlauea, where he pioneered the idea of making continuous measurements over many years rather than simply visiting a volcano once it had begun to erupt. Today, the best-monitored volcanoes are surrounded by networks of instruments that send data to observatories around the clock.

The most important of these instruments is the seismometer. As magma forces its way upwards, it fractures the surrounding rock, producing small earthquakes that are often too weak to be felt at the surface. The movement of fluids such as magma and gas through cracks generates different signals, including a continuous vibration known as tremor. A sudden increase in the number of earthquakes, or a change in their character, is frequently the first indication that something is happening beneath a volcano, and by locating each event, scientists can track whether the source is becoming shallower.

Magma accumulating underground also causes the ground above it to swell. Tiltmeters can detect extremely small changes in the slope of a volcano's flanks, and networks of satellite navigation receivers record movements of a few millimetres. Satellite radar can now map such deformation across entire regions, making it possible to watch volcanoes that have no instruments on the ground. Deformation can sometimes be dramatic. Before the eruption of Mount St Helens in 1980, a bulge on the volcano's north side grew outwards by as much as one and a half metres a day. On 18 May an earthquake caused the bulging flank to collapse in an enormous landslide, releasing the pressure inside the volcano in a sideways blast. Fifty-seven people died, a figure that would have been far higher had access to the area not been restricted.

Gases provide a third line of evidence. Magma contains dissolved gases that escape as it rises and the pressure upon it falls, rather as bubbles appear when a bottle of fizzy drink is opened. Carbon dioxide comes out of solution at greater depths than sulphur dioxide, so an increase in the ratio of carbon dioxide to sulphur dioxide may indicate that fresh magma is moving up from below. Gases can be sampled directly at vents, but this is dangerous work, and instruments called ultraviolet spectrometers now allow sulphur dioxide to be measured from a safe distance, increasingly by drones and satellites.

When such evidence is combined and communicated effectively, the results can be impressive. In 1991 Mount Pinatubo in the Philippines, which had been quiet for about five centuries, began to show signs of unrest. Scientists from the Philippine Institute of Volcanology and Seismology and the United States Geological Survey installed instruments, interpreted the rapidly changing data and issued a series of increasingly urgent warnings, and tens of thousands of people were evacuated. The eruption on 15 June was one of the largest of the twentieth century. It has been estimated that the forecasts saved at least 5,000 lives.

Scientific evidence alone, however, is not enough. In 1985 the Nevado del Ruiz volcano in Colombia had shown signs of activity for months, and a hazard map had identified the town of Armero as being at risk. On 13 November a relatively small eruption melted part of the ice on the summit, generating lahars – fast-moving flows of mud and debris – that reached Armero hours later and killed more than 20,000 people. The disaster demonstrated that warnings must be clearly understood and acted upon. The opposite risk is also real. At Campi Flegrei, near Naples, the ground rose by well over a metre in 1983–84 and tens of thousands of residents of the town of Pozzuoli were evacuated, yet no eruption followed. False alarms of this kind can make communities less willing to respond next time.

Many of the world's active volcanoes, particularly in poorer countries, still have few or no instruments on the ground, and satellites are increasingly used to fill the gaps, detecting the heat of fresh lava and the plumes of gas rising from remote summits. Researchers are also applying machine learning to the vast quantities of data that monitoring networks produce. Volcanic ash poses a further hazard to aviation, because it can melt inside jet engines. When Eyjafjallajökull in Iceland erupted in 2010, much of European airspace was closed for several days, and nine Volcanic Ash Advisory Centres around the world now track ash clouds and advise airlines on where it is safe to fly.

In December 1900 the American ornithologist Frank Chapman proposed an alternative to a holiday tradition in which hunters competed to shoot as many birds as possible in a single day: instead of killing birds, people would count them. Twenty-seven observers took part in the first Christmas Bird Count. More than a century later, tens of thousands of volunteers participate every year, and the data they have gathered form one of the longest-running records of bird populations anywhere in the world. The count is often cited as an early example of what is now called citizen science – the involvement of members of the public in genuine scientific research.

The term itself became current in the mid-1990s, when it was used in two rather different senses. For the British sociologist Alan Irwin, citizen science meant a science that responded to public concerns and drew on the knowledge of ordinary people. For Rick Bonney of the Cornell Lab of Ornithology, it described projects in which volunteers collected data for professional researchers. Irwin's version placed citizens closer to the centre of scientific decision-making, whereas Bonney's treated them chiefly as a means of gathering observations on a scale that professionals could never achieve alone. It is the second, narrower meaning that has prevailed since then, and in my view that dominance has had costs as well as benefits, a point to which I will return.

What transformed citizen science was the internet. In 2007 astronomers at the University of Oxford launched Galaxy Zoo, a website that invited members of the public to classify images of galaxies according to their shape. The response far exceeded expectations: within its first year more than 100,000 people had taken part, contributing tens of millions of classifications. Volunteers also made discoveries that no one had anticipated. A Dutch schoolteacher, Hanny van Arkel, noticed a strange glowing object near one galaxy, which turned out to be a vast cloud of gas lit up by radiation from a black hole that has since grown dim. Galaxy Zoo later grew into the Zooniverse, a platform that hosts projects ranging from transcribing historical documents to identifying animals in camera-trap photographs.

Some projects ask far more of their volunteers than simple classification. Foldit, an online game developed at the University of Washington, challenges players to fold virtual proteins into their most stable shapes. In 2011 players produced, within a matter of weeks, an accurate model of an enzyme from a virus that causes an AIDS-like disease in monkeys, a structure that had defeated professional researchers for more than a decade. Results of this kind suggest that human intuition for spatial problems can still complement the power of computers. Players have since gone on to design entirely new proteins, some of which have been successfully produced in the laboratory.

The most common objection to citizen science concerns the quality of its data. Volunteers are, by definition, not trained scientists, and it is reasonable to ask whether their observations can be trusted. The evidence is more reassuring than critics often assume. Reviews of the subject have found that, for many tasks, volunteers perform comparably to professionals, particularly when projects provide clear instructions and training, and when each item is examined by several people so that individual errors can be detected and corrected.

Statistical methods can also adjust for biases, such as the tendency of birdwatchers to visit places that are easy to reach. The online database eBird, launched in 2002, has accumulated more than a billion bird observations in this way, and its records are now used routinely in published research.

A more serious problem, I would argue, concerns who takes part. Surveys of participants in many projects suggest that volunteers tend to be disproportionately well educated and relatively affluent, which undermines the claim that citizen science democratises research. It also shapes the data: observations cluster in the places where such people live and spend their leisure time, leaving other areas poorly covered. And when participants are treated simply as unpaid assistants who collect data but have no say in what questions are asked, the arrangement can look less like a partnership than like a source of free labour. Some projects have begun to address this imbalance by working with schools and community groups in under-represented areas, but such efforts remain the exception rather than the rule.

Advocates frequently claim that taking part increases public understanding of science. That may well be true, but the evidence is thinner than the confidence with which the claim is made. Many studies rely on participants' own reports of what they have learnt, and people who volunteer for scientific projects are likely to be interested in science already. Studies that test participants' knowledge before and after a project, rather than simply asking them, remain relatively rare. Projects that hope to change attitudes or knowledge should therefore measure those outcomes as carefully as they measure their scientific results.

This is where Irwin's broader vision deserves renewed attention. In some projects, communities themselves identify a problem, such as air pollution near an industrial site, and work with scientists to design the study and interpret the results. Such projects are slower and harder to manage than a website that asks volunteers to click on images, but they offer something that conventional research often lacks: the trust and local knowledge of the people most affected. Citizen science has already proved that the public can contribute to research. The next challenge is to ensure that research contributes to the public as well.