Magma forces its way between layers of rock and solidifies as large flat areas of igneous rock, for example Fair Head, County Antrim.
3. Dykes Magma slices across rock layers and solidifies forming walls of basalt or granite running perpendicular to the rock layers. They are very common in volcanoes where magma forces its way through fissures in the cone and then cools. They add strength and support to the cone, acting like a ribcage for the volcano.
4. Laccoliths
Magma seeps between rock layers pushing them upwards and cools to form dome-like structures.
5. Lopoliths These form in a similar way to laccoliths except the weight of magma causes the rock layers to sag downwards.
Dyke Lopolit Strata Sill
Sedimentar y rocks
Fig. 14 Basalt Dyke, County Down
OLCANOES
Laccolith Batholith
Ancient mass of magma that pushed into crust and
solidified slowly
3.7 Positive and negative effects of volcanoes Fig. 15 Exam Diagram: Internal volcanic landforms
Positive effects
1. New land created – Surtsey Island, Iceland and Hawaii – a physical and economic benefit.
2. Geothermal energy – New Zealand and Iceland – an economic benefit. 3. Fertile soil after lava has been weathered and eroded – Terra Rossa soils in the Canary Islands and Brazil – a physical, economic and social benefit. 4. Minerals – sulfur rock outcrops in Malaysia – an economic benefit.
5. Tourism – geysers – Old Faithful Geyser in Yellowstone National Park and Iceland – economic and social benefit.