1A2 Geography9th February 2015

Objectives:To review the interior structure of the Earth, plate boundaries, and volcanic activity.

Homework:

• Find an example of a volcanic eruption that has produced positive/negative results for a region.

The Earth’s Interior

• Four main layers of the Earth’s interior:

1. Inner core: Solid – consists of iron & nickel. Intensely hot.

2. Outer core: Semi-molten. Also intensely hot.

The Earth’s Interior

3. Mantle: Thickest of the layers. Consists of magma (molten/melted rock).4. Crust: Earth’s outer layer. Not one whole piece – divided into sections called plates. These move due to convection currents in the magma.

Convection Currents

• The intensely hot inner and outer cores heat the magma in the mantle, causing it to move in a circular motion.

• This leads to the formation of convection currents.

Tectonic Plates

• Earth’s crust is not one whole piece. It is broken into sections called plates. These plates do not remain stationary, they move due to convection currents in the mantle.

Plate Boundaries

• Due to plate movement, sections of the Earth’s crust are pulling away from each other (constructive boundaries), colliding with one another (destructive boundaries), or sliding past one another (passive boundaries).

Mid-Ocean Ridges

• Magma can reach the Earth’s surface when it rises through gaps between plates.

• There, it cools and hardens.

• This process continues over time. The magma builds up and forms new land in a ridge-like shape.

Mid-Ocean Ridges

• Under the Atlantic Ocean, the American Plates are pulling away from the Eurasian and African Plates.

• This movement is resulting in the creation of fissures (gaps), that allow magma to reach the surface, where it has cooled and built up to form an underwater chain of mountains – the Mid-Atlantic Ridge.

Volcanic Islands

• Over time, the mid-ocean ridges can increase in size as magma continues to flow from the fissures.

• As a result, these mountains can appear above the water’s surface forming volcanic islands, e.g. Surtsey.

Volcanic Mountains

• Sometimes, cracks will form in the Earth’s crust.

• These will be filled by magma rising from the mantle.

• As this magma rises, it melts the solid rock around it, creating a huge reservoir, called a magma chamber, in the crust.

Volcanic Mountains

• The build-up of pressure in the chamber can force magma to the surface through a narrow tube, called a vent, in the Earth’s crust.

• This causes eruptions – often explosive.

Volcanic Mountains

• Lava (magma that has reached the surface), ash and gas are thrown into the air.

• This lava and ash settles around the vent and gradually builds up to form a cone shaped volcanic mountain.

• Further eruptions add layers to the mountain.

• It is eventually left with a hole at the top, called a crater, through which the lava flows.