Restless Earth • Structure of the Earth• Composition of the layers of the Earth• Convection currents• Earthʼs magnetic field• Global distribution of plate boundaries• Types of plate boundary• Types of volcano

Structure of the Earth:

The Earth is made up of a series of different layers, the outer layer is the Crust which floats on a molten layer of rock called the Mantle. This layer is above the Outer Core and Inner Core.

The crust and upper part of the mantle are also called the Lithosphere. Whilst the molten area of magma directly below this is often called the Asthenosphere.

Composition of the Earthʼs Layers:

The Crust layer is made of either Oceanic Crust or Continental Crust. The continental crust is much thicker than the oceanic crust but is made of material that is less dense.

Beneath the crust the upper part of the mantle is also solid like the crust and this combined solid layer is the Lithosphere. Just below this is the molten rock magma layer of the mantle. This flowing upper layer of the mantle affects the lithosphere and causes volcanoes and earthquakes.

Convection Currents:

Convection currents in the mantle are caused by heat generated by the core. This heat is due to radioactive decay of unstable elements in the core. As heat rises from the core it causes the molten rock in the mantle to move, which in turn leads to the movement of the section of the Earthʼs crust called Tectonic Plates above it.

The liquid outer layer of the core is made of iron and as it moves it creates a magnetic field much like an electrical dynamo.

Global Distribution of Plate Boundaries:

The Earthʼs crust is split into separate pieces called tectonic plates. Where one plate meets another is called a Plate Boundary.

Types of Plate Boundary:

There are four different types of plate boundaries, depending on which direction the plates are moving.

Plate Boundary Example Earthquakes Volcanoes

Conservative San Andreas Fault, California USA.North American and Pacific Plate slide past each other.

Destructive earthquakes up to magnitude 8.5.Small tremors almost daily.

No volcanoes.

Constructive Iceland on the Mid-Atlantic Ridge. The Eurasian and North American Oceanic Plates are pulling apart.

Small earthquakes up to 6.0 on the Richter Scale.

Not very explosive or dangerous.Erupt in fissures (cracks in the crust).Runny basalt lave eruptions.

Destructive Andes Mountains in Peru and Chile. Nazca Oceanic Plate is subducted under the South American Continental Plate.

Very destructive, up to magnitude 9.5.Tsunamis can form.

Very explosive destructive volcanoes. Steep sided cone shaped. Erupt with andesitic sticky lava.

Collision Zone Himalayas. Formed as the Indian and Eurasian Continental Plates push into each other.

Destructive earthquakes up to magnitude 9.0.Landslides are triggered.

No volcanoes.

Earthquakes and volcanoes (tectonic hazards) occur at plate boundaries. Different plate boundaries produce different hazards. The direction of plate movement and the type of plate (oceanic or continental) dictate what type of hazard will occur.

Types of volcano:

At hot spots (cracks in the surface of the crust) constructive and destructive plate boundaries different types of volcano will form. These are constructed from different types of lava and erupt in different ways.

Made from Andesitic lava, which is very sticky. Causes violent eruptions. Made from layers of ash and lava.

Made from Andesitic lava that has erupted into cinders. Often causes small but violent eruptions.

Gentle sloping volcanoes made from runny Basaltic lave which erupts in gentle lava flows.