Some AQA Hazards questions/answers

Taken from the 2021 Assessment materials.

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Here are some AQA materials from the 2021 Covid assessment exemplars.

[Note I cannot provide the Figures due to copyright].

Outline the process of liquefaction. (4)

Liquefaction refers to the process where soils with a high-water content lose their mechanical strength when shaken violently during an earthquake. They then behave like a fluid. This is observed in areas which have loose, unconsolidated sandy soils which are saturated in lowland areas. Liquefaction was a major secondary hazard in the Christchurch earthquake in 2011.

Figure 9a shows the number of global reported disasters between 1990 and 2017. It also shows the economic costs associated with the reported disasters. Figure 9b shows information about the global reported disasters for 2017 as shown in Figure 9a.

Analyse the data shown in Figure 9a and 9b.  (6)

[NB the two vertical scales on Figure 9a are confusing – it is likely that students will give erroneous supportive evidence when making valid statements]

The economic costs of global disasters (Figure 9a) have varied greatly between 1990 and 2017. The largest cost was in 2011 when the Tohoku earthquake occurred ($390 billion) and the lowest was in 2001 when the costs were a mere $40 billion. There have been three other years when the economic costs have been $250 billion or more – 1995 (the Kobe earthquake), 2005 (hurricanes Katrina and Wilma) and 2017 (three more hurricanes in the USA). It is clear though that there has not been an increase in costs over the period – they have fluctuated. Nor has there been an increase in the actual number of reported disasters. If anything, they may have decreased since 2000 after quite a sharp increase in the late 1990s.

Figure 9b provides more detail about global reported disasters in 2017, when as shown above there were three major storm events in the USA – Harvey, Irma and Maria. It is not surprising then that the storms including hurricanes dominated the economic costs, at over 80%. However, in terms of occurrence and the number of deaths, it was floods that was the more dominant feature at 38% and 34% respectively.

Figure 10 shows a wildfire on Saddleworth Moor, Greater Manchester, UK on 27 June 2018.

[Note: Saddleworth Moor is an upland area north-east of Manchester. The soils are composed of peat. In June 2018, there was a heatwave which was accompanied by virtually no rain and a dry wind for several weeks. Around 150 soldiers and fire-fighters were called in to tackle the blaze. The blaze lasted for weeks and may have been started deliberately.]

Using Figure 10, and your own knowledge, assess the potential issues associated with managing an event such as this. (9)

The area affected is clearly extensive with multiple sources of fire and hence the fire covers a large area. Such a large area will require substantial work from fire-fighters, and these will have to be brought in from a number of brigades in the region. A single unit cannot fight such a fire. Accessibility is another issue as this is an upland area. Getting large, heavy and cumbersome equipment up to such relatively remote locations is likely to be extremely challenging.

The weather appears to be presenting another major issue. The lack of rainfall, prolonged heat and very dry conditions means that new fires are likely to start. Added to this there appears to be a strong easterly wind which will make containing the fire even more difficult. The moorland is composed of peat which is a flammable material. This means that the fire can spread underground making it almost impossible to manage without extensive rainfall.

Evacuation of the area will be another issue. In this case the smoke is blowing westwards towards the north of Stalybridge. This will present a major health and safety issue for the local people, and something that the local authorities may have to consider in terms of moving people with breathing difficulties and those with asthma. Evacuation may be required particularly for the elderly or infirm. The smoke will also cause transport issues. The smoke causes poor visibility and where the fire is close to roads it will make travel very dangerous, especially for emergency vehicles. It is likely to require road closures and re-routing of vehicles.

Finally, the fact that the fire may have been started deliberately is a major concern. Managing the fire itself is a problem but other arsonists may copy the original offenders exacerbating the issue for the local emergency services into the future.

How far do you agree that secondary impacts of volcanic eruptions present a greater long-term threat to people than primary impacts? (9)

The primary impacts of a volcanic eruption are immediate and arise directly from the event. On the other hand, secondary hazards are triggered as a result of the primary impacts and occur in the aftermath. I shall discuss the relative threat of these in relation to Mount Merapi, Indonesia which erupted in October/November 2010.

Mount Merapi is an active strato-volcano located in central Java. Thousands of people live on its flanks, with villages as high as 1700 m above sea level. Merapi is situated at a subduction zone, where the Indo-Australian plate is sliding beneath the Eurasian plate. Recent eruptions have become more explosive, with viscous andesitic lavas.

In late October 2010 lava from an eruption on the mountain began flowing down the Gendol river valley – a primary impact. In addition, large clouds of ash were spewed from the mountain, with some pyroclastic flows down its slopes – both primary impacts. Merapi erupted again in early November sending further huge volumes of ash into the atmosphere. The government ordered a 15km wide exclusion zone and the evacuation of 75,000 people. Over 300 people were killed by mid-November, so the effect of these primary impacts was significant.

Heavy rain during early November triggered lahars with mixtures of water and rock debris cascading down the numerous rivers on the slopes of the volcano. These were secondary impacts and caused the evacuation of over 300,000 people, a larger number than the original evacuation. These eruptions and subsequent volcanic ash plumes caused disruption to aviation movements across central and western Java. Some flights to and from Bandung and Jakarta were also affected and international and domestic airlines suspended operations into and from those cities. These were also secondary hazards and extended the volcano’s impact over a wider area and longer time scale. For example, the Volcanic Ash Advisory Centre in Darwin, Australia, reported a sulphur dioxide cloud over the Indian Ocean between 12000 and 15000m, in the upper troposphere. Neither of these resulted in deaths though.

It is clear that the secondary impacts of Mount Merapi extended both the size of area affected, and the time period after the initial event, so it could be argued that they do provide a greater long-term threat to people than primary impacts, although the death toll did reduce.

With reference to a multi-hazardous environment that you have studied, assess the view that the underlying cause(s) leading to the hazards is human activity rather than physical factors. (20)

Los Angeles (LA) is located on the west coast of the USA in southern California. It has grown rapidly to become a huge mega city extending over 80km from west to east with a population of over 16 million. It exists in a multi-hazardous area with earthquakes, coastal flooding, wildfires, mudslides and smog.

As the city has sprawled, more and more land has gone under concrete and tarmac, particularly in the surrounding hills. With the lower infiltration rates, surface run off is much more rapid and floods are increasingly common. Mudslides are also more common, especially in those areas where deforestation has been widespread. Both of these activities, urban growth and deforestation, are human activities rather than physical events.

Coastal land-sliding, made worse during periods of heavy rain, is a major risk. Landslides are common along long stretches of the coastline of LA and regularly destroy homes and property.  During El Nino storm events increased erosion takes place at the toe of landslides on the coast whilst heavy rain saturates the soil increasing pore water pressure and lubricating potential slide planes. In this part of California there is the ever-present threat that earthquakes will trigger further movement on unstable coastal slopes. These hazards are much more linked to physical factors than human activities.

Perhaps the most significant threat to California’s coast is future climate change.  Estimates for sea level rise in California resulting from climate change range from 30-45cm by 2050 and 60-140cm by 2100.  Levees already protect many coastal areas from high tides and El Nino storms. By 2100, up to 500,000 people and $100 billion worth of property could be at risk from coastal flooding. Climate change is very much a human-induced event, though the outcomes of it are largely physical.

In addition, many beaches could narrow as sea levels rise increasing the incidence of large waves which cause cliff retreat.  Unless costly new coastal flood defenses are built, sought-after beach front properties are likely to suffer from increasingly frequent inundation and eventual abandonment. Many beach front homes in Santa Monica are below the cliffs, and just above current high tide level. Behind these are larger hotels and apartment developments. Both locations are vulnerable to increased sea level and the accelerated cliff erosion that would accompany it. Although these are physical events, the fact that such properties exist is largely due to human activity.

Wildfires appear to have become an almost annual event in the LA region. Most wildfires are caused by either accidental or deliberate human actions. Between July and November (the ‘fire season’) hot, dry Santa Ana winds drive wildfires up and down the canyons and hills of southern California’s coastal mountains, close to the suburbs of LA.  These areas are increasingly popular residential locations. Housing development is often surrounded by scrubland, called chaparral, providing fires with plenty of tinder-dry fuel.  The reasons behind these fires are more due to human activity, but with the assistance of physical factors.

Los Angeles covers a vast area and this has tended to encourage the use of private vehicles rather than the development of a comprehensive public transport system. Car exhaust fumes have been the major factor in the decline of air quality in the Los Angeles basin. Photo-chemical smogs are now common, and almost entirely due to human activity.

In conclusion, it is clear that the underlying causes of hazards in the LA region are due more to human activity, although it is the physical endogenous factors of the region that have made them be more severe.