One of the most iconic views in southern England, Beachy Head is the highest chalk cliff in Britain, rising 162m (531 feet) above the sea.
Even those who have never been here might well recognise the cliffs from such films as Chitty Chitty Bang Bang and James Bond: The Living Daylights.
What, for me, makes these magnificent cliffs awesome is not just just their beauty, but how they came into existence. They are made up of the compressed shells of billions of generations of microscopic shellfish which once floated in the sea, died, and sank to the ocean floor. Their shells formed a very thin layer over the seabed. Slowly, millimetre by millimetre, over the course of 30 million years, this layer of shells grew to become more than 400 metres thick, compressed by massive forces into chalk. I feel humble alongside these cliffs.
Where did all this chalk come from?
The origins of the famous chalk cliffs date back a 100 million years, to a time when dinosaurs were the dominant animal species on land. Until about 175 million years ago, the land-mass of the world had been almost entirely contained in a single supercontinent Pangaea. Over the next 100 million years, this supercontinent slowly split apart. North America began to split away around 170 million years ago, creating the North Atlantic ocean, then the south atlantic began to open up around 140 million years ago. The third major stage of the Pangaea break-up occurred around 100 million years ago, when India drifted northwards away from Africa and Antarctica, opening up the Indian ocean.
As continents move apart, new oceans are formed, and new ocean floor is created by magma rising from below. As well as displacing the water, magma heats up the ocean, forcing sea-levels to rise and encroach onto the land. Volcanic activity also creates greenhouse gases which further warmed the planet, preventing the formation of polar ice caps. In this environment, that of a warm planet with deep oceans, chalk was able to form in the sea-ways of the newly-flooded continents.
Microscopic skeletons of plankton descended these ocean floors over the next 30 million years. Their tiny shells, made of calcium carbonate, were easily broken down, and formed lime mud. The mud grew in thickness slowly, at a rate of just over a millimetre every hundred years. Over the course of 30 million years, this bed of lime mud grew to be around 400m thick, solidified by pressure from above into chalk. The process occurred in numerous places around the globe, and gave the period its geological name – the cretaceous period, from the Latin word for chalk, creta.
Chalk and limestone
Insofar as it is formed by the skeletons of microscopic sea creatures, the formation of chalk is similar to that other limestones. Why are they so different?
Most limestone is carboniferous limestone, and this provides the basis of much of the landscape Britain. It was formed much earlier than chalk, around 340 million years ago, the time when the first amphibious creatures were leaving the sea and learning to live on the land. Although the climate was warm, the seas were much shallower, meaning that a lot of sediments were eroded and washed from the land, and mixed with the calcium deposits on the sea floor. It is these impurites that explain why limestone is disoloured, and rarely as white as chalk. The shallow carboniferous seas also contained a wide variety of crustaceans, while chalk beds are comprised almost entirely of the skeletal remains of microscopic plankton.
The raising of the Downs
Around 65 million years ago, a further movement of tectonic plates saw Africa creep northwards and begin a collision with Eurasia. This collision (the Alpine Orogeny), the effects of which continued until a couple of million years ago, created the Alps, Pyrenees, and Carpathian Mountains of central Europe. The effects in England, far from the epicentre of the collision, were less dramatic, but enough to cause the chalk bed to buckle, and raise a long mound, several hundred metres high, stretching across southern England. This ridge is known to geologists as the Weald-Artois anticline. The top of the mound eventually eroded away, revealing older sanstones between the two chalk escarpments of the North and South Downs.
The coming of the English Channel
The final stage in the story of the creation of Beachy Head, began much more recently, around 450,000 years ago. A huge freshwater lake had formed in the area that is now the North Sea, fed by rivers such as the Thames and the Rhine, as well as the meltwater of huge ice sheets formed during the last three ice ages. The Weald-Artois anticline acted as a natural dam holding back this lake. Eventually, in a series of catastrophic events – 450,000, 160,000, and 90,000 years ago – the dam was breached, and the waters forced their way through, destroying the isthmus connecting England to continental Europe and creating the English Channel. It is estimated that each flood would have lasted several months, releasing a million cubic metres of water every second and, between them, carving out the English Channel as we know it today.
As the last Ice Age ended and sea levels rose, further erosion of the cliffs helped shape the Beachy Head we see today. This process of erosion continues at a surprisingly rapid pace – 30 to 40 cm of these chalk cliffs disappear every year.
Beachy Head is a fascinating place. This post has looked at the cliffs themselves, but other posts look more closely at the lighthouse, and the memorials on top of the headland.
The downland behind the cliffs is wide and open, and great for walking. Views to the west are dominated by the Seven Sisters, while to the east is Eastbourne.
The Seven Sisters is a favourite walk, and we will visit these unique cliffs in another post.
Beachy Head lies a couple of miles south west of the town of Eastbourne. Take the main A259 towards Newhaven, and it is signposted to the left. There is a car park which costs £1.40 for two hours. There are numerous lay-bys on the minor road between Beachy head and Birling Gap, but all have a ticket machine and cost the same.