Tectonics in the British Isles Flashcards
What volcanoes are present in the British Isles?
No active volcanoes present.
Extinct ones e.g. Arthur’s seat, Edinburgh.
Formed by an extinct volcano system of Carboniferous age (approx. 350 million years).
Was eroded by west-east moving glacier during the Quaternary (approx. the last two million years).
Exposing rocky crags - west.
Tail of material - east.
What are the intrusive features of the British Isles?
Batholiths, sills, dykes.
E.g. Isle of Arran, Scotland.
How many earthquakes does the British Isles get?
Intraplate earthquakes.
200 per year - 175 unnoticeable
An earthquake of 3.7 ML or larger every 1 year.
An earthquake of 4.7 ML or larger every 10 years.
An earthquake of 5.6 ML or larger every 100 years.
Where do most earthquakes of the British Isles occur?
Western side of the British mainland.
Almost completely absent from eastern Scotland and north east England, and Ireland.
What has been the biggest/most damaging occurrence of an earthquake in the British Isles?
Dogger Bank in 1931 - 6.1 magnitude.
Most damaging UK earthquake - Colchester, 1884.
1,200 buildings needed repairs, chimneys collapsed and walls were cracked.
Why does the British Isles get earthquakes, despite being located away from any plate boundaries?
Still squeezed by motion of the Earth’s tectonic plates. Northern Britain is also still being uplifted due to the melting of the ice sheets.
Deformation - occasional earthquakes.
What is the most recent largest earthquake in the British Isles?
The Market Rasen 2008 Earthquake - Lincolnshire.
5.2 magnitude.
Epicentre 4 km north of Market Rasen.
15 miles south-west of Grimsby.
Caused by sudden motion along a strike-slip fault - 18.6km below.
Actual motion - 2 minutes.
Most intense for just 10-30 seconds.
Maximum vertical ground motion at the epicentre of the earthquake was only ~1 mm.
What plates are the British Isles distantly being squeezed by, causing earthquakes?
Intraplate earthquakes.
Combination of E–W North Atlantic Ridge and N–S African Plate regional stress fields, and local mantle conditions.
What were the impacts of The Rasen Market 2008 earthquake?
0 deaths.
1 broken pelvis from a falling chimney.
St Mary Magdalene church - spire damaged - £100,000.
LITTLE IMPACT.
What is a volcanic plug and where can one be located within the British Isles?
Magma hardens within a vent on an active volcano.
Can cause an extreme build-up of pressure if rising magma is trapped underneath - explosive eruptions.
E.g. extinct volcanic plug - Edinburgh’s Castle.
Where can basaltic flows be located within the British Isles, and what sort of rocks occur there?
Antrim lava plateau formed in Northern Ireland.
Lava cooled, vertical cracks in the flow resulted in hexagonal columns.
E.g. the Giant’s Causeway.
Granite.
