Hazardous environments Flashcards

Question

Explain how the nature of bedrocks influences earthquake damage. (liquefaction)

Answer 1

Some materials are vulnerable to becoming 'jelly-like' when shaken - this is called liquefaction and is commonly associated with clays and silts. Liquefaction occurs when compacted sediments lose strength and stiffness in response to applied stress such as shaking from an earthquake. Material that is ordinarily solid behaves like a liquid. Liquefaction most often occurs in saturated, unconsolidated sandy soils. This is because loose soils have a tendency to compress when a load is applied. The loss of soil structure due to compression causes an increase in pore water pressure, reducing internal strength and causing the the surface to act like quicksand. The result of liquefaction is that building foundations may become unstable and slopes become vulnerable to mass movement. Many building in Mexico City became tilted following the 1985 earthquake when the lake bed sediments on which which much of the city is built became liquefied.

Answer 2

Although LIC/MICs may have building design standards in place, regulations are rarely enforced. For instance, in Mexico City in 1985 several modern high-rise buildings collapsed, with approximately 30000 people killed. Furthermore, earthquakes are often perceived as infrequent problems in a society facing daily struggles for survival.

Answer 3

In countries where there is a higher level of economic development there is much done to prepare for earthquakes. For instance, schools in Japan run regular earthquake drills, some as often as once a month. Also, Japan has buildings erected on shock absorbers. This means that when an earthquake starts, the resulting movement will impose less stress on the structure of the building.

Answer 4

In 2002, a series of earthquakes lasting 10 hours killed 800-1000 people, injured 4000 and left approximately 20000 homeless in a remote region in the Hindu Kush mountain range 150km of Kabul. The was severe damage and loss of life as: -Afghanistan is war-torn and one of the poorest countries in the world with Approximately 85% of them live on less than one dollar (1$) a day. Afghanistan therefore did not have the resources necessary to cope with the aftermath of the earthquake. -Houses had heavy roofs for insulation which simply collapsed burying their occupants. -Although the earthquake wasn't especially powerful, it was a shallow earthquake occurring at a depth of 8km close to the boundary of the Eurasian and Indian plates.

Answer 5

A major earthquake measuring 7.1 on the Richter scale occurred near to the north east coast of Taiwan about 80km Northeast of Hualien. The earthquake caused the death 5 people with more than 200 injured. The damage and loss of life wasn't as severe as the Afghan earthquake because: -The epicentre of the earthquake was not particularly lose to built up areas. -Taiwan is significantly wealthier than Afghanistan and is therefore better able to prepare and react to an earthquake. -Modern buildings.

Answer 6

-Experience, the more experience of environmental hazards the greater the adjustment to the hazard. -Material well-being, over 500 million people currently choose to live on or near active volcanoes and this number is set to grow due to dramatic population growth of LICs around the Pacific basin.

Answer 7

Affluence too poor to move. Education about the risk-perception that it may not happen to them. Soil fertility is a pull factor-employment. Employment tourism, Iceland attracted 2.2 million tourists as of 2023 Geothermal power (Iceland). Culturally/historically pull factors. Fatalistic, they feel that it cannot controlled so therefore nothing can be done. No eruptions in their lifetime so the perception of risk is reduced.

Answer 8

are more suitable than multi-storey structures as the threat of collapse over roads and evacuation routes is reduces.

Answer 9

Safer houses can be built cheaply - tyres filled with stones or sand and fastened between floor and foundation can serve as affordable shock absorbers. Similarly, adobe (i.e. cheap sun-dried brick) walls can be reinforced with a strong plastic mesh installed under plaster; in the event of an earthquake these walls crack but do not collapse, thereby reducing loss of life.

Answer 10

The Volcanic Explosivity Index (VEI) is a scale that describes the size of explosive volcanic eruptions based on magnitude and intensity. The numerical scale (from 0 to 8) is a logarithmic scale. The scale is based on the volume of magma erupted (magnitude) and the eruption column height of explosive eruptions.

Answer 11

As pressure is released, gases dissolved in the magma bubble out so the composition of the lava changes. Most eruptions are formed by the eruption of hot basalt magma. Lava flows are seen in both lava dome and shield volcanoes. Pahoehoe forms from mainly basaltic lava flows which are rich in iron, silica, magnesium and calcium. This basalt rock has a low silica means the flow of the lava would have been less viscous therefore fast flowing. Aa has a more viscous flow whose surface is covered by thick, jumbled piles of loose, sharp blocs.

Answer 12

Acidic rain is often hydrochloric or sulfuric based due to the emissions of sulphur and plume gases. Volcanic acid rain has a PH of 2.5. to 5. Acid rain pollutes surface water, enhances chemical weathering and can damage crops. (example)

Answer 13

Most commonly found on composite volcanoes due to the steeper gradient. It is a slide or flow of mass caused by volcanic eruption carrying large volumes of matter down the volcano's slope. Volcanic landslides can rage in size from less than 1km3 to more than 100km3. Volcanic landslides can travel over 100km/h. The high velocity and great momentum of landslides allow them to cross valley divides and run up slopes several meters high.

Answer 14

Tyres filled with stones and sand that are can be fastened between the floor and foundation of the building. This can serve as cheap-ground motion absorbers. However, such as house is approximately only a third as strong as one built on more sophisticated shock absorbers, but it would costs much less and is a more economically viable solution for developing countries.

Answer 15

In theory, by altering fluid pressure deep underground at the point of greatest stress in the fault line, a series of small and less damaging earthquakes may be triggered. This could release energy that would otherwise build to to create a major earthquake. Additionally, a series of underground controlled nuclear explosions might relieve stress before it reached difficult levels.

Answer 16

Distortion of fences, roads and building are some examples; changing levels of water in boreholes. As strain from earthquakes can change the water-holding capacity or por

Answer 17

Hazards mapping is undertaken to show areas of ground that are likely to liquefy, fault locations and dates of past movements, past earthquake epicentres and dates and areas where landslides and tsunami's might result.

Answer 18

Earthquake monitoring involves the measurement of ground vibrations known as seismology. Seismometers convert vibration from seismic waves into electrical signals displayed as seismograms. This enables the detection and measurement of earthquakes. The Global Seismograph Network (GSN) is a digital network of geophysical sensors connected by telecommunications networks. This data can be used to determine the location and size of an earthquake and to accumulate historic records of earthquakes that can be used for future forecasting. Geoscientists can provide information about these matters, and can engage with local authorities and communities to ensure that this information is used effectively to minimise risk to people and property. They are likely to undertake this vital work only if their roles and those of others are clearly defined and they feel confident that they can offer geoscientific advice which meets high professional standards without fear of retribution Laser beams can be used to detect plate movement. Radon gas escapes from cracks in the Earth's crust. A sudden increase in the radon gas can be monitored, indicating an earthquake. Existing building can be retrofitted to withstand earthquakes, but this is expensive and may not be affordable for LICs withstand earthquakes, but this is much more expensive than doing so at the time of construction. It is also essential that the local population are aware of the risks and know how to act during an earthquake. This can be a particular challenge in areas which are not frequently seismically active, where there may be no memory of large earthquakes.

Answer 19

-Measuring seismic activity with seismometers. Seismic activity always occurs as volcanoes awaken and prepare to erupt. -Tiltmeters and GPS satellites monitor any changes in the landscape. Volcanos tend to swell near an eruption. -Monitoring gases escaping from a volcano using chemical sensors. Often there is an increase in the concentration of Sulphur dioxide near an eruption. -Measuring temperature - volcanoes becoming become hotter when magma starts to rise through the mina vent. -Looking at the past history of eruptions. (more on this)

Answer 20

Hazard maps were produced by the Icelandic Meteorological Office (IMO). The Hazard maps included real-time and archived information on volcanic hazards with lava fields from previous eruptions being marked as dangerous terrain, playing an important role in advising both the government and the public.

Answer 21

The United States Geological survey produces National Hazard Maps to show the distribution and probability of earthquake shaking levels in the United States. These maps were created to provide the most accurate and detailed information possible to assist engineers in designing buildings and other infrastructure that will withstand shaking from earthquakes in the United States.

Answer 22

reduce the impacts of hazard on property land life.

Answer 23

The Indian Ocean tsunamis were generated by a massive earthquake that measured 9.0 on the Richter scale. There was sudden slippage along the destructive plate margin where the Indo-Australian plate is being subducted beneath the Eurasian plate. This slippage caused the Eurasian plate to rebound upwards by about 15-20m, causing the displacement of water. The massive column water rose and split to form two tsunamis, one travelling east towards the Sumatra island of Indonesia and the other west and north of Thailand, India and Sri Lanka. Tsunamis can also be generated by large underwater landslides such as the past landslide events on the continental slope off Norway with a tsunami reaching northern Scotland.

Answer 24

volcanic activity. They have shallow foci (0-70km deep) and are usually submarine so are of minimal hazard to people. (clarity on which plate boundaries cause more damage)

Answer 25

silica content (rhyolite, the most viscous type of lava, is composed of over 70% silica) and relatively low temperatures (600-900oC). So, lava is viscous and gas babbles, which do not escape easily, build up to create highly explosive eruptions.

Answer 26

Tsunamis are not very common in the Indian Ocean. Between 1982 and 2002, 157 tsunamis were recorded worldwide of which only 19 were outside the Pacific region. This meant that the coastal communities in countries such as Indonesia and Sri Lanka were unaware of the dangers posed by tsunamis and completely unprepared to cope. Most of the island chains in the Indian Ocean, such as the Maldives, are flat and low-lying. Fishing villages and tourist towns were built right up against the waters’ edge to make maximum use of the beaches. As a consequence, the tsunami rolled well inland bringing widespread destruction to vast swathes of the coastline and inundating entire islands. Much of the Indian Ocean coast is densely populated. There are thriving fishing communities and, in recent decades, tourism has flourished. Large numbers of people were at risk from the tsunamis

Answer 27

Hot runny lava with low silica content produces gently sloping shield volcanoes with associated effusive Hawaiian eruptions. Effusive eruptions pose a limited threat to people; they are usually associated with lava flows that pose more a threat to property than life. Cooler viscous lava with high silica explosive eruptions, producing ash columns that extend many tens of miles into the stratosphere and that spread out into an umbrella shape. These large eruptions produce widespread deposits of fallout ash. Eruption columns may also collapse due to density to form thick pyroclastic flows. The eruption of Mount Pinatubo in 1991 sent a plume of tephra 30km high into the atmosphere. For rhyolite, lava domes can volcano, leading to a build up in pressure and a subsequent lateral blast through a weakness in the side of the volcano. Lateral blasts can produce a variety of direct hazards, including ballistic projectiles which can be thrown to distances of at least 10 km and pyroclastic flows which can travel at high speed to distances of more than 30 km.

Answer 28

Formed at a divergent boundary, Nyiragongo's lava is low in silica and therefore flows rapidly posing a danger to life and property. The nearby city of Goma was inundated by two lava flows, which caused substantial socioeconomic disruption and forced the mass exodus of the population, leaving nearly 120,000 people homeless Despite being an effusive eruption, the 2002 was devastating due to the Democratic Republic of Congo's exposure to the hazard and the people's vulnerability. Over half a million live on the flank's of Nyiragongo for fertile soil, with the majority of the population living in poverty with a high dependency on subsistence agriculture. Coupled with this, war in the area for the past decade has increase the population vulnerability to the hazard.

Answer 29

Terracing involves the shaping of slopes into steps. When mass movements occur the waste is captured and accumulates on the flat steps and impeded from readily sliding or flowing down the slope. Afforestation etc. Netting or mesh can be placed over a slope in order to stabilise it. This form of reinforcement contains any falling debris or rock to beneath the netting, which limits the hazards. Furthermore, netting is particularly effective at increasing the stability of slope by preventing rock falls. Grading involves flattening steep slopes to decrease their gradient. This directly reduces the gravitational forces acting on the slope material, making it less susceptible to movement. Additionally, grading techniques can improve surface water drainage as the slope is given a more uniform topography, directing water away from vulnerable areas of the slope. This reduces water saturation in the soil, which is a common trigger for mass movements.

Answer 30

Earthquake Early Warning (EEW) is the prompt detection of a potentially damaging earthquake within a few seconds from its onset. The lead time for EEWs is very short (seconds to fractions of a second). Although this does not seem to give much time to act, it is possible to trigger rapid risk mitigation measures such as the emergency braking of high-speed trains or shutting off gas pipes before the earthquake waves reach their location. EEWs can be sent to smartphones to enable people to adopt safe behaviours.

Answer 31

Prediction means specifying the exact time and exact location of an event. Although the location of fault lines is known, the exact time and location of future earthquakes cannot be predicted as no diagnostic precursor has yet been discovered. A diagnostic precursor is a signal indicating a high probability of an earthquake happening in a very small period of space and time. Instead, scientists concentrate on improving earthquake forecasting, based on probabilities of events occurring in a region over a given time period. A further difficulty is that earthquakes originate beneath the ground, often many kilometres down, so data gathering depends on remote observation techniques and measuring effects at the surface. Even measuring the prevailing stress in the crust is challenging, as it requires drilling several kilometres into the ground.