Tectonic Hazards & Causes
- Created by: Lamorran Trevenna
- Created on: 14-12-16 10:26
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- Tectonic Hazards & Causes
- Tectonic Activity
- A tectonic event is the result of a movement or deformation of the Earth's crust.
- Tectonic events are usually earthquakes or volcanic eruption.
- A tectonic hazard is when a tectonic event has the potential to have an impact on people resulting in loss of life and/or physical damage to property.
- Not all tectonic events are hazardous as many earthquakes occur deep below the Earth's surface, are low in magnitude or occur far from where people are living.
- A tectonic disaster is when a tectonic event occurs and causes extensive loss of life, damage and destruction.
- The Haiti earthquake in 2010 was a magnitude 7.0 earthquake with its epicentre 25 km west of the capital city Port-au-Prince. It caused 316,000 deaths, making it one of the deadliest earthquakes of all time.
- A tectonic event is the result of a movement or deformation of the Earth's crust.
- Causes
- Convection Currents
- Convection currents are circular movements of the mantle material that rise from the core and cool as they meet the crust before falling again to return to the core to be heated once more.
- Convection Currents
- Plate Margins
- Destructive (Convergent)
- Where one plate sinks beneath another (subduction) as they collide. The upper plate crumples, creating new mountains and volcanoes.
- Constructive (Divergent)
- Where two plates are moving apart from each other. Molten rock from the mantle rises to the surface, cools and hardens, forming a ridge of new rock.
- Volcanic eruptions are common.
- Where two plates are moving apart from each other. Molten rock from the mantle rises to the surface, cools and hardens, forming a ridge of new rock.
- Conservative (Transform)
- Where two plates are sliding past each other. Pressure builds up until they move suddenly, causing earthquakes.
- Collision (Convergent)
- Where two continental plates collide and are crushed against each other. They are pushed upwards to form new mountains (fold mountains).
- E.g. The Himalayas.
- Where two continental plates collide and are crushed against each other. They are pushed upwards to form new mountains (fold mountains).
- Destructive (Convergent)
- Physical Impacts
- Extrusive Igneous Activity
- Once magma flows out (extrudes) on to the surface of the Earth it is referred to as lava, which then cools to form igneous rock.
- This process creates a number of significant landforms:
- Volcanic cones = cone-shaped volcanoes that are formed from the build-up of lava on the surface of the Earth.
- Fissures = vents on the volcano through which lava can erupt.
- Lava plateaux = flat, extensive lava fields produced by volcanic activity.
- This process creates a number of significant landforms:
- Once magma flows out (extrudes) on to the surface of the Earth it is referred to as lava, which then cools to form igneous rock.
- Different Types of Volcano
- Cinder Cones
- Volcanoes built from ejected lava from a single vent. As the lava is blown violently into the air, it breaks into small fragments that solidify around the vent to form a cone. Most cinder cones tend to have a bowl-shaped crater at the summit and do not rise above 300m in height, e.g. Mt Gordon, Alaska.
- Composite
- Typically steep-sided, symmetrical cones built from layers of lava flows, volcanic ash, cinders and bombs.
- Most composite volcanoes have a crater at the summit which can contain a central vent or a group of vents. These can rise up to as high as 2.4km, e.g. Mt Pinatubo, Philippines.
- Typically steep-sided, symmetrical cones built from layers of lava flows, volcanic ash, cinders and bombs.
- Shield
- Typically dome-shaped with gentle sides and a wide base. They are built up slowly over time from numerous balsaltic lava flows. These volcanoes can stretch for up to 6.5km and can reach 300m in height, e.g. Mauna Loa on Hawaii.
- Lava Domes
- More typically dome-shaped with steep sides and a narrow base. They are formed as viscous lava flows slowly and therefore cools on the sides of the dome, expanding it further, e.g. Soufriere Hills on Montserrat.
- Cinder Cones
- Intrusive Igneous Activity
- Intrusive igneous activity is when magma cools and solidifies within the Earth's crust. This can lead to the formation of the following landforms after weathering and erosion have exposed them at the surface:
- Batholith = a large emplacement of rock that forms from cooled magma deep in the Earth's crust, e.g. the Half Dome in Yosemite National Park, USA.
- Laccolith = magma is forced between two layers of sedimentary rock, creating a dome-shaped feature, e.g. Devil's Tower in Wyoming, USA.
- Sill = magma has intruded between layers of sedimentary rock, e.g. the Whin Sill, Northumber-land
- Dike = magma has cut discordantly across massive rock formations, e.g. Mackenzie dike swarm in the Northwest Territories, Canada.
- Intrusive igneous activity is when magma cools and solidifies within the Earth's crust. This can lead to the formation of the following landforms after weathering and erosion have exposed them at the surface:
- Effects of earthquakes on landscapes
- Earthquakes have less dramatic impacts on the landscape of the Earth.
- Rift Valleys
- Can form where two oceanic plates are diverging such as the mid-Atlantic ridge, or where continental crust is being stretched by divergence, such as in the East African Rift Valley
- Fault Scarps
- Cliff-like features that can range from a few metres to hundreds of metres in height and can be several hundred kilometres long. They also form where two plates are diverging.
- Rift Valleys
- Earthquakes have less dramatic impacts on the landscape of the Earth.
- Human Impacts
- Why do people live in tectonically active areas?
- Lack of Knowledge
- The long gap between some tectonic events means communities slowly forget that the area is at risk.
- Lack of Choice
- Some people remain living in tectonically active areas because they lack the choice or there are few alternatives. This may be especially true for very poor people who may rely on the quality of land for subsistence farming.
- Inertia
- There may be traditional, historical or cultural reasons for living close to volcanoes and this may prevent people from moving away.
- Lack of Knowledge
- Economic
- Social
- Cost to people n terms of casualties and loss of life.
- Misery, suffering and poor health
- Loss of infrastructure - damage to roads, services, electricity, water etc.
- Cost of repairing damage
- Cost of rebuilding
- Indirect costs of loss earnings, loss of tourism income etc.
- Cost of emergency operations
- Social
- Why do people live in tectonically active areas?
- Extrusive Igneous Activity
- Tectonic Activity
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