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•What is a lava plateau?

• What is a volcanic plug?

• What are basalt columns?

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Lava plateaus are formed by the large outpourings of fluid lava from long narrow openings in the crust. During each

eruption, the lava flows out from these openings, solidifies and builds up layer upon layer each time.

An example would be the County Antrim Plateau in Northern Ireland.

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About 430 million years ago the North American and Eurasian plates had

collided to form a vast range of mountains called the Caledonian

mountains- they would be fused for 370 million years.

Around sixty million years ago- the plates began to diverge.

As they diverged, huge fissures would have been created in the

landscape, this allowed magma to rise from the mantle as lava and cover the surrounding chalk rock-

these lava flows continued for over 2 million years.

As the lava cooled and formed into basalt, a vast flat plateau was

left behind.

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Volcanic Plugs

An example would Slemish in County Antrim, Northern

Ireland.

A volcanic plug is a volcanic landform created

when magma hardens within a vent in an active

volcano. If a plug is preserved,

erosion/weathering may remove the surrounding rock while the resistant

plug remains, producing a distinctive landform.

Fissures created by the divergence of the North American and Eurasian plates,

allow magma to flow from the mantle as lava.

Explosions deposited volcanic rocks around the fissure, creating a volcano;

continued deposition would have lead to a cone developing.

Lava would continue to flow from a vent in the cone, onto the surrounding

plateau.

In the vent of the cone, the magma cooled more slowly than usual, forming a harder rock than

basalt called dolerite- this plugged the volcano vent.

The less resistant rock surrounding the plug of the

volcano has been weathered and eroded over time- leaving the

distinct landscape feature.

Basalt Columns

An example would the Giant’s Causeway in

County Antrim, Northern Ireland.

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Large eruptions of basalt lava may create deep flows of molten rock. As the rock

slowly cools it shrinks slightly. The stresses cause jointing in several different planes, and columns of rock

form with a generally hexagonal shape, like

pencils.

As the North American and Eurasian plates diverged magma, as lava, rose

through fissures in the surface.

The lava cooled to form basalt, as the rock formed, contraction occurred.

Contraction can occurred with ease vertically, but horizontally this creates

cracks within the rock.

This contraction produces hexagonal columns. Quick cooling produces smaller columns, whilst

longer cooling creates larger columns.