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Tectonic Hazards

Tectonic Hazards

Tectonic hazards are threats caused by the movement of tectonic plates that have the potential to cause damage to life, property, the environment, human activity and/or the economy. The tectonic plates are either moving against, apart or past each other.

What are some examples of tectonic hazards?

Examples of tectonic hazards include earthquakes and volcanic activity, which can lead to secondary hazards such as tsunamis and landslides.

What are the possible tectonic hazards at different plate margins?

Different types of plate margins (including divergent, convergent and conservative plate margins) are responsible for different types and magnitudes of tectonic hazards, depending on the relative direction of plate movement and types of crust.

Tectonic hazards at divergent plate margins

Divergent plate margins (also known as constructive plate margins) are where the plates are moving apart from each other. These generate low magnitude earthquakes with a shallow focus.

Tectonic hazards at convergent plate margins

Convergent/destructive plate margins are where plates move towards each other, leading to high magnitude earthquakes and volcanic activity as the friction between the two plates increases and is released.

Tectonic hazards at conservative plate margins

Frequent earthquakes (up to magnitude 8) often occur at conservative plate margins, where plates are sliding past each other in a horizontal direction.

What is the global distribution of tectonic hazards?

The seven major tectonic plates and their direction of movement can be seen below.

Tectonic Plates, Distribution of Plate Tectonics, StudySmarterFig. 1 - Distribution of plate tectonics

An example of divergent plate margins is the Pacific Ring of Fire which occurs around the Pacific plate. This area contains the majority of the planet’s volcanoes, and it is also responsible for most earthquakes.

An example of a conservative plate margin is the San Andreas Fault, where the North American and Pacific plates are moving past each other and are responsible for the earthquakes in the region.

Tectonic Plates, San Andreas Fault, StudySmarterFig. 2 - San Andreas Fault. Image: faultfind_48 via Flickr CC BY-SA 2.0

The Eurasian and Indian plates are two continental crusts colliding and buckling (convergent plate margin) and have formed the Himalayas.

How do tectonic hazards cause secondary hazards?

Tectonic hazards, including earthquakes and volcanic activities, can generate secondary hazards, e.g. tsunamis and landslides.

Secondary hazards caused by earthquakes

  • Secondary hazards caused by earthquakes include tsunamis, liquefaction and landslides.

  • Tsunamis resulting from earthquakes are caused by vertical displacement of the seabed, which then displaces the water in the ocean water column.

  • Liquefaction can also be developed by earthquakes, as the ground shaking induces water particles in the soil to increase in pressure and move relative to each other. Thus leading to the reduction of the strength of the soil, sometimes damaging buildings and infrastructure as the soil is no longer able to support them.

  • Landslides are the movements of rock, earth or debris down a slope. Earthquakes create stresses in slopes and eventually the breaking and falling of weak slopes. These landslides on marine margins can create tsunamis when their mass enters the water or when water displaces behind and in front of an underwater landslide.

Secondary hazards caused by volcanic activity

  • Underwater volcanic explosions and shock waves can cause tsunamis when the energy travels through the water.
  • Pyroclastic flows (mixtures of hot volcanic rock, ash and gas), lahars, parts of the volcanoes can also cause tsunamis when their mass enters and displaces the water.
  • Lahars are mud or debris flows caused by the mixtures of volcanic material and water. They tend to create threats near the volcanoes but can travel far from volcanoes along rivers and can cause issues further away.
  • Jökulhlaups are sudden floods of water from glaciers, which can be caused by volcanic eruptions under a glacier.

What are the impacts of tectonic hazards?

As you’ve learnt so far, the impacts of tectonic hazards can occur due to secondary hazards. Further impacts of tectonic hazards include natural disasters. Natural disasters are when the natural hazard has caused significant damage to society or a community, and they can no longer cope using their own resources. This can include disruptions to human, material or environmental aspects, such as loss of life, injuries and damage to infrastructure.

Some examples include the Gorkha Earthquake, Tohoku Earthquake and Tsunami and Mount Merapi Eruption 2010. These examples demonstrate that the impacts of tectonic hazards are influenced by the socio-economic situation of the community affected.

How can we monitor tectonic hazards?

We can monitor tectonic hazards through several methods that depend on the hazard type. For instance, the magnitude of earthquakes are monitored using seismographs and uses the moment magnitude scale (MMS). We can also measure earthquakes using more observable methods such as the Mercalli scale, which determines how much physical damage was done.

The magnitude of volcano eruptions is measured using the Volcanic Explosivity Index (VEI). It is based on the volume of pyroclastic material, column height and duration of the eruptions.

Monitoring tectonic hazards are vital as it allows us to know what, where, how and when a tectonic hazard may occur. This can help us minimise the potential damage it can cause and warn people.

Tectonic Hazards - Key takeaways

  • Tectonic hazards are threats caused by the movement of tectonic plates that have the potential to cause damage to life, property, the environment, human activity and/or the economy.
  • Tectonic hazards include earthquakes and volcanic activity.
  • Divergent plate margins generate low magnitude earthquakes with a shallow focus.
  • Whilst convergent plate margins cause high magnitude earthquakes and volcanic activity and frequent earthquakes often occur at conservative plate margins.
  • An example of divergent plate margins is the Pacific Ring of Fire which occurs around the Pacific plate. The San
  • Andreas fault is an example of a conservative plate margin. The Eurasian and Indian plates are two continental crusts colliding and buckling (convergent plate margin), forming the Himalayas.
  • Secondary hazards caused by earthquakes include tsunamis, liquefaction and landslides. Secondary hazards induced by volcanic activity include tsunamis, pyroclastic flow, lahars and jökulhlaups.
  • Tectonic hazards can become natural disasters.
  • The magnitude of earthquakes are monitored using seismographs and uses the Moment Magnitude Scale (MMS).
  • The Mercalli scale determines the extent of physical damage, and the magnitude of volcano eruptions is measured using the Volcanic Explosivity Index (VEI).

Frequently Asked Questions about Tectonic Hazards

Tectonic hazards are mostly found at the plate margins. Most divergent plate margins (also known as constructive plate margins) generate low magnitude earthquakes with shallow focus. Convergent plate margins generate high magnitude earthquakes and volcanic activity. Frequent earthquakes (up to magnitude 8) often occur at conservative plate margins, where plates are sliding past each other in the horizontal direction.

Tectonic hazards can be reduced by monitoring them and finding out what, where, how and when a tectonic hazard may occur. This can help us minimise the potential damage it can cause and provide warnings to people.

A tectonic hazard is a threat caused by the movement of tectonic plates that have the potential of causing damage to life, property, the environment, human activity and/or the economy. The tectonic plates are either moving against, apart or past each other.

We can monitor tectonic hazards through several methods which depend on the type of hazard. For instance, the magnitude of earthquakes are monitored using seismographs and uses the moment magnitude scale (MMS). We can also measure earthquakes using more observable methods such as the Mercalli scale, which determines how much physical damage was done.


The magnitude of volcano eruptions is measured using the Volcanic Explosivity Index (VEI). It is based on the volume of pyroclastic material, column height and duration of the eruptions.

We can plan for tectonic hazards by monitoring them and finding out what, where, how and when a tectonic hazard may occur. This can help us minimise the potential damage it can cause and provide warnings to people.

Final Tectonic Hazards Quiz

Question

What are tectonic plates?

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Tectonic plates are the sections of the lithosphere.

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What are some examples of tectonic hazards?


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Examples of tectonic hazards include volcanic activities, earthquakes and tsunamis.

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What is continental drift?


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Continental drift is the movement of the continents of Earth after the separation from Pangaea, one large continent.

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Why was the theory of plate tectonics proposed?


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The theory of plate tectonics was proposed when the outline of tectonic plates was found in 1960 after seismographs were used to test for atomic bombs during World War II. This recorded the vibrations of earthquakes which allowed them to discover the epicentres of the earthquakes.

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What is seafloor spreading?


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Seafloor spreading is when magma fills the gap with rock as the tectonic plates move apart.

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How does palaeomagnetism explain seafloor spreading?


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Palaeomagnetism explains seafloor spreading because scientists found that some of the rocks in the ocean ground have magnetic signatures in opposite directions to the rocks next to them. This indicates that the new magnetic alignment is the magma that fills in between tectonic plates.

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What is mantle convection?


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Mantle convection is the movement of magma due to its variation in temperature and density, which also causes the tectonic plates to move.

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What is subduction?

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Subduction is when the denser tectonic plate is pushed underneath the other plate.

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What is slab pull?


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Slab pull is the gravitational pull that causes the denser plate to further move after subduction.

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What are the different layers within the structure of Earth?


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The different layers within the Earth are the crust, mantle, outer core and inner core.

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How many major tectonic plates are there?


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There are seven major tectonic plates.

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What are some named examples of tectonic plates?


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Examples of tectonic plates are the African, Antarctic, Eurasian, Indo-Australian, North American, Pacific and South American tectonic plates.

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What is the continental crust made of?


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The continental crust is made of granite rock that comprises quartz, feldspar, and other relatively lightweight material, mostly silicon and aluminium.

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What is the oceanic crust made of?


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The oceanic crust is made of basaltic rock and other materials, predominantly silicon and magnesium.

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How do tectonic plates float on the mantle?


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Tectonic plates float on the mantle due to the composition of the rocks within the plates that make them less dense than the mantle.

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What are tectonic processes?


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Tectonic processes are interactions between tectonic plates that impact the structure of the Earth’s crust.

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Why do tectonic processes occur?


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Tectonic processes occur due to the movement of tectonic plates relative to each other. The cause of the movement of tectonic plates can be summarised by mantle convection, subduction and slab pull.

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What occurs at divergent plate boundaries?


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At divergent plate boundaries (also known as constructive plate boundaries), the plates are moving away from each other. This occurs as the convection current of the mantle pushes the plates apart, generating a gap in between, causing magma to fill the gap and producing a new crust.

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What are the consequences of divergent plate boundaries?


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Most are located at ocean ridges and generate low magnitude earthquakes. Divergent boundaries between continental plates often form rift valleys.

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What occurs at convergent plate boundaries?


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Convergent/destructive plate boundaries are where plates are moving towards each other. When an oceanic crust and a continental crust meet, the denser oceanic crust is pushed below the continental crust (also known as subduction). The oceanic crust underneath is destroyed in the process. When continental plates collide, it can also cause either one or both of the plates to buckle up.

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What are the consequences of convergent plate boundaries?

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When an oceanic crust meets with another oceanic crust, subduction also occurs. Island arcs and oceanic trenches are often created. When continental plates collide, it can also cause either one or both of the plates to buckle up, consequently forming mountain ranges.

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What occurs at conservative plate boundaries?


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The regions where plates are sliding past each other in the horizontal direction are called the conservative plate boundaries or transform plate boundaries. Due to the irregularity of the surface of the plates caused by rocks, the friction and pressure build-up and the plates eventually slide past each other, causing frequent earthquakes.

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What are the consequences of conservative plate boundaries?


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The rocks from the plates are pulverised and often create fault valleys or undersea canyons.

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What are the impacts of tectonic plate movement?

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The movement of tectonic plates relative to each other leads to tectonic processes, which are interactions between tectonic plates that impact the structure of the Earth’s crust. Tectonic processes can lead to tectonic hazards.

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Earthquakes are measured with _______.

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Seismographs.

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What is the proper sequence of an earthquake?

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First, plates generate friction; second, stress is released; third, seismic waves are produced; fourth, seismic waves travel through the crust.

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Secondary effects of earthquakes include:

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Tsunamis and liquefaction.

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The focus of an earthquake is also known as the epicentre.


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False.

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An earthquake epicentre is best defined as:

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The point on the surface of the Earth above the focus of an earthquake.

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What is the scale most commonly used by scientists to measure earthquake strength?


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Moment Magnitude Scale (MMS).

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In which area is an intraplate earthquake most likely to occur?


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New Madrid Seismic Zone.

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It quaked on the boundary of the North American and the Pacific plates. This was an interplate earthquake.

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True.

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Earthquakes at divergent plate margins tend to be _______ earthquakes at convergent plate margins.


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Weaker than.

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A 9.0 earthquake is focused at 350km below the Earth's land surface. Plate margins are likely _______ at the focus.

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Convergent.

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An earthquake in California has a shallow focus, magnitude of 7.5, and numerous aftershocks. It likely occurred because of slippage along a _______ plate margin.


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Conservative.

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Types of earthquake waves include


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Primary, Secondary, Love, and Rayleigh.

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A seismic wave that travels under the ground and compresses and dilates rocks is a(n) _______ wave.

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P wave.

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A low-frequency, crustal seismic wave with side-to-side motion is a(n) _______ wave.

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L (Love).

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Which is the correct statement?

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Crustal fracturing causes buckling.

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What are volcanoes?

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Volcanoes are openings of the Earth’s crust to the molten rock below the surface of the Earth.

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How are volcanoes formed at convergent plate margins?

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Volcanoes are formed at convergent plate margins due to the process of subduction. As the denser plate sinks, the temperature and pressure increase. The increase in temperature and pressure causes rocks to release water, resulting in a reduction in the melting point of the rock above. This forms magma, which rises to the surface, forming a volcano.

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How are cinder cones formed?


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Cinder cones are formed by the particles from lava that erupt from a single opening. In the process of the gaseous lava being ejected into the air, small fragments solidify, forming cinder. This falls around the opening and forms a circular or oval cone.

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How are composite volcanoes formed?


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Composite volcanoes are formed by alternating layers of lava, volcanic ash, cinders, blocks, and bombs. They are often steep-sided and symmetrical cones.

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How are shield volcanoes formed?


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Shield volcanoes are formed by fluid lava flow. Lava pours out in different directions from the opening or a group of openings. This builds a gently sloping surface.

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How are lava domes formed?

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Lava domes are formed by lava that is too viscous to flow far. Therefore, the lava often remains around the vent, building the volcano from within. This process includes the outer surface hardening, breaking, and falling down the sides of the volcano.

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What are the characteristics of volcanoes at divergent plate margins?


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Volcanoes are generally small at divergent margins because basalt lava has a low viscosity and low gas content.

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What are the characteristics of volcanoes at convergent plate margins?


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Volcanoes at convergent plate margins tend to erupt frequently and with high force. This is because the magma from the process of subduction has high gas and silica content. Ocean-ocean convergent plate margins tend to consist of volcanic islands.

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What are the hazards caused by volcanoes?


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The hazards caused by volcanoes include lava flows, pyroclastic flows, ash falls, gas eruptions, and further secondary hazards.

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How can lava flow be a threat?


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Volcanoes can erupt with lava flow (molten rock) and damage nearby infrastructure. However, it tends to travel slowly, which allows time for evacuation.

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How can pyroclastic flows be a threat?


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Pyroclastic flows are eruptions of rock, ash, and gas that are superheated. They can travel at 80km/h, significantly faster than lava flows. This means that they can travel a long way with little warning. Therefore, they can be a threat to nearby people and cause widespread death and destruction through burning.

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