Tectonic Hazards

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.

Fig. 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.

Fig. 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.