- When a magma plume (a stationary rising stream of magma with a bulbous head) burns through the crust, allowing the magma to reach the surface a hot spot in the plate is created.
- The magma cools and forms a cone, eventually ending up as a volcano.
- As the plate moves the volcano is taken with it, cutting off it's supply of magma making it extinct.
- A new cone is then formed and the process repeats.
- This eventually over time creates an island chain where each volcano is younger than the previous.
- Example= Hawaii moving NW at 10cm a year. The currently active volcano is Mauna Loa.
Form when magma is rising slowly or the crust is thick, so magma solidifies. Can be recognised by doming in the land, but mainly seen when erosion exposes the rocks.
Batholiths - Dartmoor, Shap and Skiddow Lake District.
Type = vertical cutting accross bedding planes
Characteristics = large (cover 100km), dome shaped, coarse grained
Formation = an injection of magma into the crust rises and fractures/melts the rock above.They cool slowly and cause a metamorphic aureole by altering the surrouding rocks using heat and pressure. Such as limestone turning to marble.
Dykes - Isle of Arran.
Type = vertical that cut accross bedding planes
Characteristics = horizontal cracks parallel to the surface from contraction during cooling
Formation = force open existing fractures and open channels through cracks by magma injection. They can radiate around a batholith in a dyke swarm.
Sills - Great Whin Sill causing waterfals e.g. High Force, River Tees
Type = Horizontal parallel to bedding planes.
Characteristics = vertical cracks as it contracts, parallel to existing layers
Formation = magma is intruded along bedding planes which provide a weakness for the flow of magma to exploit along. Earth movements can change the…