Edexcel IGCSE Geography

Revision Notes

3. Hazardous Environments

What is a hazardous environment in geography?

A hazardous environment in geography refers to a place or area where the natural or human-made conditions are likely to cause harm or damage to people, property, or the environment. Hazardous environments can be caused by a variety of factors, such as natural disasters, environmental degradation, pollution, or human activities.

Hazardous environments can pose a threat to human health, safety, and well-being, as well as to the natural environment. They can also have social and economic impacts, such as displacement, loss of livelihoods, and increased poverty.

The main hazards studied in GCSE physical geography are earthquakes, volcanoes and tropical cyclones. Geographers study hazardous environments to understand the causes and consequences of these hazards, as well as to develop strategies to mitigate their impact. This can involve identifying high-risk areas, assessing vulnerability, and developing emergency preparedness plans.

What are tectonic hazards?

Tectonic hazards are natural hazards that are caused by the movement of tectonic plates. Tectonic plates are the large pieces of the Earth's crust that move slowly across the surface of the Earth, interacting with each other at plate boundaries.

Tectonic hazards can be caused by a variety of plate tectonic processes, such as earthquakes, volcanic eruptions, and tsunamis. These hazards can have significant impacts on human populations and infrastructure, causing damage to buildings and other structures, as well as injuries and fatalities.

Earthquakes are one of the most common tectonic hazards and occur when two tectonic plates move against each other, causing the ground to shake. Earthquakes can cause landslides, liquefaction, and tsunamis, which can have devastating impacts on coastal communities.

Volcanic eruptions are another common tectonic hazard and occur when molten rock, ash, and gas are released from a volcano. Volcanic eruptions can cause damage to buildings and infrastructure, as well as impacts on air quality and the environment.

Tsunamis, which are large waves caused by earthquakes or volcanic eruptions under the ocean, can also be a significant tectonic hazard. Tsunamis can cause flooding, damage to infrastructure, and loss of life.

Tectonic hazards mainly occur at the plate boundaries; this can be clearly seen when looking at maps of earthquakes and eruptions.

distribution-of-earthquakes

distribution-of-volcanic-eruptions

What are the different plate boundaries?

There main types of plate boundary are:

1. Constructive/divergent plate boundaries: These are areas where two tectonic plates move away from each other, creating a gap between them. This process is known as seafloor spreading, and it results in the formation of new oceanic crust. Constructive/divergent plate boundaries can be found along mid-ocean ridges, such as the Mid-Atlantic Ridge.

2. Destructive/convergent plate boundaries: These are areas where two tectonic plates move towards each other and collide. Depending on the type of plates involved, convergent plate boundaries can create different features, such as mountain ranges, volcanic arcs, and deep ocean trenches. The types of destructive/convergent plate boundaries:

- Oceanic-continental: When an oceanic plate collides with a continental plate, the denser oceanic plate will typically subduct beneath the continental plate, forming a deep ocean trench and a volcanic mountain range.

- Collision boundary (Continental-continental): When two continental plates collide, neither plate can subduct due to their buoyancy. Instead, the plates will typically crumple and fold, forming a mountain range.

3. Transform plate boundaries: These are areas where two tectonic plates move past each other horizontally. Transform plate boundaries are characterized by large faults, and they can result in earthquakes. The most well-known transform boundary is the San Andreas Fault in California.

What is a hotspot?

A hotspot refers to a location on the Earth's surface where there are active volcanoes that are not on or near a plate boundary. Hotspots usually occur as a result of a mantle plume. A mantle plume is a column of hot, molten rock that rises from deep within the Earth's mantle, and reaches the surface in the form of a volcanic eruption.

hot-spot

Hotspots are different from plate boundaries, which are the regions where tectonic plates interact with each other. Hotspots are instead thought to be the result of a stationary, fixed source of heat within the mantle that remains relatively stable over time, while the Earth's plates move over them.

The volcanoes formed by hotspots are typically shield volcanoes, which are characterized by their broad, gently sloping cones. The Hawaiian Islands are one of the best-known examples of hotspot volcanism, with the active volcano of Kilauea being a particularly famous example. Other examples of hotspots include the Yellowstone hotspot in the United States and the Reunion hotspot in the Indian Ocean.

Why do earthquakes happen?

Earthquakes are caused by the sudden release of energy that has built up in the Earth's crust, resulting in seismic waves that move rapidly through the ground.

The movement of the tectonic plates creates stresses within the Earth's crust, which can build up over time and cause rocks to deform and break. When the stresses reach a critical point, the rocks suddenly jolt, releasing energy in the form of seismic waves. The point of rupture is called the focus, and the point on the Earth's surface directly above it is called the epicenter.

features-of-an-earthquake

The energy released in an earthquake is measured on the Moment Magnitude scale. Larger earthquakes release more energy and can cause more severe shaking, ground rupture, and other hazards such as landslides and tsunamis.

Earthquakes can occur anywhere in the world, but they are most common along plate boundaries. The type of earthquake that occurs depends on the type of plate boundary and the direction of movement between the plates. For example, at a constructive/divergent boundary, where two plates are moving away from each other, shallow earthquakes occur along the boundary as new crust is created. At a destructive/convergent boundary, where two plates are colliding, earthquakes can occur both shallow and deep along the boundary as well as within the subducting plate. Shallow and deep earthquakes can also occur on transform boundaries where plates are moving past each other.

What are the different types of volcano?

Cone or composite and shield volcanoes are two types of volcanoes that are formed by different types of volcanic eruptions and have distinct physical characteristics.

Cone/composite volcanoes, also known as stratovolcanoes, are steep-sided cones made up of layers of ash, lava, and other volcanic debris. These volcanoes are typically found near subduction zones where two tectonic plates collide, with one plate being pushed down into the Earth's mantle. Cone volcanoes are formed by explosive eruptions that release large amounts of ash, lava, and gas. The lava is viscous, meaning it is thick and sticky, and it can pile up around the vent of the volcano, creating the steep sides of the cone. Some famous examples of cone volcanoes include Mount St. Helens in the United States, Mount Fuji in Japan, and Mount Vesuvius in Italy.

Shield volcanoes, on the other hand, are broad, gently sloping volcanoes that are shaped like a shield. They are typically formed by effusive eruptions that release lava that is low in viscosity, meaning it is thin and flows easily. The lava flows out of the vent and spreads out over a large area, gradually building up the broad, shield-shaped volcano. Shield volcanoes are typically found at hotspots and along mid-ocean ridges. A well-known example of shield volcanoes is Mauna Loa in Hawaii.

What are the main impacts of tectonic hazards?

Volcanoes and earthquakes can have significant impacts on the natural environment, human populations, and infrastructure. Some of the main impacts of these hazards include:

Loss of life and injury: Volcanic eruptions and earthquakes can cause significant loss of life and injury due to the shaking, ash fall, lava flows, and other hazards associated with these events.

Damage to infrastructure: Buildings, roads, bridges, and other infrastructure can be damaged or destroyed by earthquakes and volcanic eruptions, leading to disruptions in transportation, communication, and other essential services.

Economic impacts: The destruction of infrastructure and loss of life and property can have significant economic impacts on local communities and the wider region. This can include the loss of jobs, damage to businesses, and the need for costly rebuilding and recovery efforts.

Environmental impacts: Volcanic eruptions can release large amounts of ash, gases, and other materials into the atmosphere, which can impact air and water quality and cause harm to plants and animals. Lava flows and ash fall can also destroy ecosystems and habitats.

Social impacts: Volcanic eruptions and earthquakes can cause significant social disruption, including the displacement of people from their homes and communities, the loss of cultural and historical sites, and the psychological impacts of living through a traumatic event.

What are tropical cyclones and their effects?

Tropical cyclones, also known as hurricanes, typhoons, or cyclones, are large rotating storms that form over warm tropical oceans. 

AeyIbqo0_tropical-cyclone-distribution

Their main characteristics are strong winds, heavy rainfall, and storm surges which can cause significant damage to coastal areas.

Tropical cyclones are formed when warm, moist air rises from the ocean surface and begins to rotate, fueled by the Earth's rotation and the release of latent heat. As the storm grows, the rotating winds can reach speeds of over 74 miles per hour, forming an eye in the center of the storm with clear skies and calm winds.

tropical-storm-formation

Tropical cyclones can cause a range of hazards, including strong winds, heavy rain, storm surges, and flooding. These hazards can result in damage to buildings, infrastructure, and crops, as well as loss of life. The intensity and impact of a tropical cyclone can vary depending on a number of factors, including the size and strength of the storm, the location and terrain of the affected area, and the level of preparedness and response of the affected population.

Tropical cyclones are typically classified based on their wind speeds using the Saffir-Simpson Hurricane Wind Scale. The scale ranges from Category 1, with winds of 74 to 95 miles per hour, to Category 5, with winds over 157 miles per hour.