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Landscape features: Just the facts

Updated Wednesday 27th September 2006

Take a journey around Britain and discover some of our fascinating geology. For a richer experience, you can explore with our interactive Geology Toolkit.

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Dartmoor Copyrighted image Icon Copyright: BBC

Every geological event in the history of the United Kingdom has left its mark.

Traces of a volcanic eruption millions of years ago still exist as well as beaches left high and dry by a retreating ice age.

 

Giant's Causeway
Raised beaches
Wasdale Screes
Malham Cove
Nant Ffrancon
Dartmoor

 

Map showing areas of the UK Copyrighted image Icon Copyright: Used with permission

The Giant's Causeway, County Antrim, Northern Ireland
Around 50 or 60 million years ago a volcano erupted in this part of what is now Northern Ireland. Basalt lava flowed out onto the surface of the ground, and as it cooled, it formed thousands of spectacular polygonal shaped columns, the tallest of which is now 40 feet high.

In some places the solidified lava is 90 feet thick. The tops of the lava columns form stepping-stone type structures, which leads from the cliff foot and into the sea. These are about 30 cm across and are mostly hexagonal, although some five-sided examples can be seen.

The Giant's Causeway is made up of about 40,000 of these pillars of basalt, creating a spectacular landscape feature that is the focus of local legend. Successive eruptions created layers of basalt, which are visible in the cliff's edge.

Raised Beaches of Scotland
100,000 years ago Scotland was covered by a gigantic ice sheet. The massive weight of the ice depressed the land beneath it and for thousands of years the coastline etched its signature into the rock.

When the last ice age ended, about 10,000 years ago, the retreating ice sheet released its water and the land started a process known as the “glacial rebound”. The land began to rise, taking with it the cliffs and beaches that for centuries formed the coastline. Over the millennia the coastline has changed, leaving a stepped landscape that illustrates ancient sea levels.

The result are the magnificent raised beaches of Scotland. Much of the rock in this area is sedimentary, formed on the ocean floor, and later deformed as faults in the Earth’s crust tilted the strata to vertical. Some areas are made of granite, where molten rock pushed its way into the sediments and cooled slowly. The softer sedimentary rock has eroded away to leave the granite outcroppings.

The Wasdale Screes, Lake District
The valleys of the Lake District have been scoured and scarred by the movement of glaciers, producing the well known 'U'-shaped cross section. The valley floors became deeply gouged, producing the rock basins that are today occupied by lakes. The deposition of glacial debris, in the form of clays or moraines has in places formed natural dams behind which lakes have formed. Wast Water sits in one such valley. It is the deepest lake in England at around 78 metres deep, about three miles long and half a mile wide.

Since the retreat of the glacier, silting and erosion has created huge fans of scree on the lake’s south shore, originating from a high mountain from which stones and earth continually tumble. On the west of the lake lies the village of Wasdale.

The geology of this area is some of the oldest in Europe. It was a centre of volcanic activity when these mountains were formed. Originally the mountains were twice as high as they are today, but weather and erosion have reduced them to a mere 978 metres at their highest (Scafell Pike).

Malham Cove, Yorkshire - Limestone Scarps
The astonishing limestone escarpment at Malham Cove stands 80 metres high and some 300 long. It is a curved cliff of carboniferous limestone that formed sometime after the last ice age. Its craggy curved surface was formed as meltwater from Malham Tarn cut its way backwards as it fell over the edge as a waterfall. The erosion cut away more material from the lip of the waterfall than from the edges, creating the curved shape.

These days water does not flow over the escarpment, what water there is makes its way instead down deep fissures in the limestone. At the top of the scarp lies a magnificent limestone pavement, deeply grooved and cracked by uneven weathering by slightly acidic rain. The pavement formed by the rain etching existing cracks in the pavement, dissolving away the rock until a fissure was formed.

The resulting limestone pavement comprises 'clints' and 'grykes', where the naked limestone lumps are the clints and the fissures in between are the grykes.

Nant Ffrancon Valley, North Wales
Wales is one of the most southerly points in the UK to have experienced the ice age and subsequent glaciation during the Pleistocene Epoch. The Welsh ice fields were centred on the Migneint plateau and the Arenig mountains, and glaciers from this sheet radiated out from its centre. These glaciers carved out the spectacular glacial trough valleys of Nant Ffrancon and Llanberis/Nant Peris (Snowdonia) and Tal-y-Llyn (Cadair Idris).

Nant Ffrancon valley is a classic 'U' -shaped glacial valley. Large boulders on the valley floor were deposited as the glacier receded. The curved basin valley floor is the product of post-glacial sedimentation, created by an ancient valley floor lake. It currently is the home of what is known as a 'misfit stream', a small stream that wanders across the valley floor. A 'misfit stream' is so named because it does not carve the valley itself, but is rather is the drainage from a landform created by other means.

Dartmoor - Granite Tors
Most of Dartmoor consists of a single type of rock - granite. This granite was formed in the Carboniferous/early Permian period, around 280 million years ago. Mysterious granite tors dot the landscape, on summits, steep valley edges, at the edges of the two great plateaux and close to the main river gorges. They were formed by weathering.

The exposed granite usually has both horizontal and vertical jointing, the vertical ones probably the result of the granite cooling during formation, and the horizontal ones usually follow the surrounding landscape, a result of pressure being released as surrounding rocks were released by erosion.

The jointing in the surface of the rock allows acid water to seep into the rock. The freezing and thawing of water (helped by four ice ages) jacked open the breaks in the rock. Blocks of granite were levered away by this process, leaving the tor isolated and exposed, littering the ground beneath with boulders and rubble.

 

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