- Volcanoes are when hot liquid rock or ash and gases erupt out of the ground. The ground is called the earth’s crust or lithosphere and is mainly made of rock. The hot liquid rock is called magma when in the earth, or lava when exposed to air. The reason the lava or ash erupts is due to the movement of the earth’s tectonic plates.
Types
Of Plates:
- There are 4 main types of plates – constructive, destructive, conservative and collision.
- Constructive margins move apart and create gaps for lava to come out e.g Iceland.
- Destructive margins are where oceanic plates subduct beneath the continental plate and melt to release magma into the Benioff zone, magma rises slowly through the crust and will then erupt e.g The Philippines.
- Volcanoes can also occur at hotspots, area of upwelling of magma in the mantle where magma is in weaknesses in the earth's crust and erupt as a volcano e.g Hawaii
Earthquakes:
- Earthquakes are when sudden and violent shaking of the earth’s crust occurs, due to processes in the earth’s crust (i.e. tectonic plates moving). This is called seismic activity. The plates are moved by convection currents in the earth’s mantle. Huge pressure and stress build up between moving plates: when these stresses are released as fault lines slip, the energy is released as shaking the ground. This is an earthquake.
- Earthquakes occur at ALL plate boundaries. The greatest earthquakes, or ‘seismic activity’, occurs at destructive and conservative margins.
- There are also ‘intra-plate’ earthquakes which occur away from plate margins.
Tsunamis:
- Earthquakes can cause ‘tsunamis’. These are very powerful waves in the ocean that can cause very damaging coastal flooding.
- They mainly occur at destructive margins. When the plates slip, the upper plate moves up very quickly. The sudden upward thrust pushes up the ocean water, creating a bulge in the ocean surface (vertical water column displacement). The energy then ripples out as waves (like throwing a stone in a pond). As the tsunami waves approach the coast, the front of the wave slows when it hits the shallower shore water, and the back of the wave catches up, creating a taller huge wave. This then floods the land.
- The convergent/destructive plate margin areas of the ocean-coast cause the highest magnitude tsunamis e.g. the Philippines, Japan. i.e. ‘the ring of fire’ around the Pacific Ocean.
- Smaller tsunamis can occur elsewhere, for example from landslides into seas or oceans.