The Science of a Beautiful Landscape
The Dorset and East Devon Coast is well known to be very beautiful. The reason for that is in the relationship between the rocks and the sea.
A coastline takes shape through the sea and the weather pounding rocks and beaches over tens of thousands of years. The nature of a coastline depends on how the rocks and beaches react to the relentless energy from the sea and The Jurassic Coast has lots of different rocks that react in a wide variety of ways. The World Heritage Site is crammed with exceptional examples of natural coastal landforms of almost any kind imaginable. It is so rich in these features that scientists that study coastal landforms have described the World Heritage Site as an outdoor laboratory.
Scientists have spent years coming to study the landforms but many thousands of people come every year to enjoy the sheer beauty that all this variety creates.
Old Harry Rocks
Location: Handfast Point, near Studland
Landform type: Chalk
Age: 10,000 – 20,000 years old
Where to go: you can walk to the Handfast Point from Studland, or, for a longer and more challenging route, from Swanage. Alternatively you can take the scenic 11km hike along the spectacular Chalk Ridge from Corfe to the coast.
Look out for: On a clear day it is easy to see the Isle of Wight!
Old Harry's fate
The string of sea stacks that trail out onto the sea off the point here formed after the last age. At some point in the last 20,000 years the sea breached the chalk ridge that would have stretched across to the Isle of Wight. It probably did this by flooding up river channels that had cut down through the chalk. Once this natural barrier was breached the land behind was submerged, creating the Solent. The chalk was slowly stripped back to create the coastline we see now. Sea stacks like Old Harry form when slightly harder areas of rock resist erosion whilst everything else around them is worn away. Eventually these stacks will collapse (Old Harry once had a wife, who is sadly no more) but new ones will replace them. Ongoing erosion like this is the main reason the coast is so beautiful.
Durlston and Swanage Bay – discord in the rocks
Location: Swanage, Dorset
Ladform Type: transverse coastline
Age: approximately 20,000 years
Where to go: the town of Swanage has its seafront in Swanage Bay and is popular with visitors. Durlston Bay can be viewed from Peverille Point, near Swanage or from Durlston Head in Durlston Country Park.
Look out for: the dramatic landscape of Purbeck is prodiced by the underlying geology. The soft rocks from the valleys and the hard rocks, like The Chalk, from the ridges.
Discord in the rocks
The eastern coast of Purbeck slices through lots of different types of rock. To the south there is hard Portland stone that forms sheer cliffs. Following the coast north the softer Purbeck beds are exposed and carved into Durlston Bay. Peverille Point is a spur of hard rock from the top of the Purbeck Beds. Beyond lies the wide sweep of Swanage Bay, created by the erosion of the soft Wealdon Beds. Then, beyond that the next headland is formed by hard rock again, this time the Chalk. This is a very different shape to the Durlston Cliffs (link?) where the same rock type is exposed in the cliffs for several miles and the shape of the coast varies very little.
Looking at Swanage Bay and Durlston Bay makes the relationship between the rocks and the shape of the coast quite obvious. It becomes even more clear when you look at what each cove contains. Durlston bay has no beaches, just rubble from the collapsed layers of limestone. Swanage bay on the other hand has broad sandy beaches as there is a lot of Sandstone in the Wealdon Beds.
Features like these, and those found to the west (Durlston Cliffs, Lulworth Cove and Durdle Door) make this stretch of coast, running almost as far as Weymouth, internationally famous with scientists and visitors alike.
Durlston Cliffs – The Pounding Sea
Location: Durlston Country Park
Ladform Type: Plunging cliffs (and a section of 'longitudinal coast')
Age: 10,000 years
Where to go: visit Durlston Country Park and take a stroll along its winding footpaths to the cliff top.
Look out for: The abandoned quarries at Tilly Whim Caves - men would have quarried blocks of Portland stone here to load straight onto waiting boats. The shelves and crevices in the sea cliffs are home to the second largest Guillemot colonies on the South coast.
"that iron cliff-face which lies between St. Alban's Head and Swanage" - J. Meade Falkner
Although the cliffs around Durlston are not as high as others on the Jurassic Coast they plunge vertically down into the sea to a depth of several metres. They are an imposing wall of rock and constantly battered by the sea. The constant exchange between a volatile sea and an unmoving cliff face can be an intense thing to witness:
"Yet, though the rock looks hard as adamant, the eternal washing of the wave has worn it out below, and even with the slightest swell there is a dull and distant booming of the surge in those cavernous deeps; and when the wind blows fresh, each roller smites the cliff like a thunder-clap, till even the living rock trembles again."
This is from 'Moonfleet' by J. Meade Falkner. An adventure set in Dorset.
Lulworth Cove and Stair Hole – Picture Postcard Science
Landform Type: Limestone, clay, sandstone and chalk
Age: 10,000 years old
Where to go: Lulworth Cove is accessed via Lulworth Village. There is pay and display parking and a summer bus service no X53.
Look out for: the hard rocks at the mouth of the cove erode much more slowly than the rocks behind giving the cove its horseshoe shape.
The perfect cove
The rock layers on this part of the coast have been folded so that they stand almost vertical. Hard Portland and Purbeck Stone forms the cliffs with much softer Wealdon Clay, Gault and Greensand behind with the chalk forming the back of the cove. The attractive form of Lulworth Cove formed of the way these different rocks erode.
At some point in the past the river here would have punched a hole in the hard Portland Limestone that formed the cliffs. Once the sea could breach those rocks it quickly eroded the much softer rocks behind, widening the gap and creating the rounded cove. This process has happened in several places along the coast here and is still happening today. At Man 'O War Cove to the west two old coves have been eroded to form one with only a string of reefs showing where the Portland Stone once was. And Stair Hole just next to Lulworth is a new cove in the making. Eventually it will join up with Lulworth Cove.
Having all these features so close to each other makes this is an internationally renowned place for studying how bays and headlands form.
Durdle Door – The Rock Arch
Location: Durdle Door near Lulworth
Landform Type: Limestone
Age: Jurassic 140 million years old
Where to go: Durdle Door is accessed via Lulworth or Winfrith villages. There is pay and display parking available through the caravan park. The walk down to the cliff top and then beaches is steep and can be prone to erosion.
Look out for: Fossil ripple marks in the rock slabs at beach level, next to the arch. Donut shapes embedded in the rock around the top of the arch – these are remnants from a fossil forest!
The Rock Arch
Hard layers of Portland Limestone have been folded on this part of the coast so that they appear almost vertical and these form the seaward edge of the small promontory here that includes Durdle Door.
The impressive natural arch of Durdle Door formed due to the effect of the erosive power of the sea on the vertical layers of different types of rock. At some point in the past the sea would have begun to breach the hard Portland Limestone and form a string of caves along the coast. The much softer rocks behind would have quickly been eroded away creating caves and natural arches. Eventually the arches collapsed leaving stacks, which would in turn be broken and washed away by the power of the waves.
Durdle Door is part of only a small strip of hard Portland limestone that is left here. The remnants of old arches can still be seen in the form of 'stumps' of limestone only just visible in the waves. One day that is all that will remain of Durdle Door. See what Durdle Door will look like in the future.
More information on Durdle Door - The Natural Arch
Chesil Beach – the finest barrier beach in Europe
Location: Chesil Bank (West Bay – Portland) Best viewed from Abbotsbury Hill or New Ground view point, Portland.
Landform type: Long shingle bank up to 15m high made largely of chert pebbles.
Age: approximately 10,000 years
Where to go: Chesil is a very large landform. From the viewpoints of Abbotsbury Hill or New Ground on Portland you can get a sense of its size. You can go onto the beach at West Bay, Burton Bradstock, Abbotsbury, Ferry bridge or Chiswell on Portland. Some areas are protected and under restricted access to protect nesting birds.
A new Chesil Beach visitors centre will be opening in 2012. We need to expand on the centre once it is finished
Look out for: the pebbles that make up the beach are sorted by the waves so the small ones are at the western end and the largest ones at the eastern end. Chesil bank also supports its own unique plant and animal communities.
Building a beach
130,000 years ago sea levels were at a similar level to those of today and the cliff line of West Dorset would have been in almost the same position as it is now. During that time the landslides and mudflows that characterise that part of the Jurassic Coast would have been moving, carrying thousands of tonnes of debris on to the beach to be slowly removed by the sea. However, at about 125,000 years ago sea levels dropped due to the formation of ice sheets and the old coastline was stranded. The landslides continued to occur along the cliffs but without the sea to remove the fallen material it built up into massive debris fans. Eventually the slopes formed a stable angle, stopped moving and became vegetated. After 100,000 years the ice age ended and sea levels rose again to their previous height and began eroding the old landslides. The material was carried east by long shore drift creating the enormous shingle bank we see today. With the accumulated debris from the ice ages however, there aren't enough pebbles to sustain the size of Chesil bank and the huge beach is slowly shrinking. It will take thousands of years for it to disappear entirely.
Golden Cap – highest point on the South Coast
Location: a headland between Charmouth and Seatown, Dorset.
Landform type: 191m (626ft) high cliff.
Age: Cliff face formed in the last 10,000 years. The flat top of Golden Cap is a preserved land surface 50 million years old.
Where to go: You can get to Golden Cap by foot along the South West Coast Path or by a short walk from the National Trust Car Park on Langdon Hill.
Look out for: On a clear day from the top of Golden Cap you can see Dartmoor!
Aim for the flat-top!
The name 'Golden Cap' comes from the golden coloured Cretaceous sandstone that forms the top part of the cliff. The 'golden' cap sits on top of much older Jurassic rocks and there is an unconformity (link to unconformity info) between them.
When the towering cliffs of Golden Cap collapse in landslides thousands of tonnes of rock spill out into the sea. On a calm day from the top of the Cap old 'boulder arcs' can be seen stretching out under the water. These are the remnants of old landslides, and they can be traced 0.5km into the bay, showing how the cliff line has retreated over thousands of years.
The curious flat top of the Cap is a remnant of a very ancient landscape. 50 million years ago, during the Eocene Epoch this whole region would have been part of a plane, eroded flat over several million years. Some time in the last 40 million years the region was lifted up and rivers carved down into the plane leaving small patches preserved on hill tops. Golden Cap is one such place. To the north of the Cap there is a chain of flat top hills, all with flat tops, all acting like a memory of an almost vanished landscape.
Lyme Regis to Golden Cap – soft stuff
Location: West Dorset
Landform Type: Soft cliffs - a mixture of active landslides and mudflows supporting a nationally rare habitat type.
Age: recently active from around 20,000 to the present day
Where to go: It is dangerous to go up into the landslides and people have to be rescued from mudflows almost every year. Stay on the beach or on the coast path, away from the cliff edge.
Look out for: Fossils! Natural erosion here releases fossils onto the beach. Visit the Charmouth Heritage Coast Centre for more information.
Landslides to be proud of
This is an exciting part of the World Heritage Site. It demonstrates very clearly the important role of natural erosion in creating a place so special and worthy of protection. Scientists have been able to relate the way the cliffs collapse here to how the beaches below are maintained making it possible to monitor change and make predictions about what might happen in the future.
Landslides are a type of natural erosion and keep the geology of the World Heritage Site exposed to be studied. As well as playing this important role, the constantly shifting ground amongst the landslides and mudflows creates a habitat known as 'soft cliffs'. Soft cliff habitats are rare nationally and support several rare species of insect as well as a glorious variety of wild flowers and plants. Black Ven is the richest soft cliff habitat in the country. All these elements – the globally important geology and fossils and the nationally important habitat – rely on the constant activity of the landslides to be maintained. Without natural erosion we wouldn't have them, and we wouldn't have a World Heritage Site.
The Undercliffs National Nature Reserve
Location: Between Axemouth in East Devon and Lyme Regis in Dorset.
Landform Type: the 'undercliff' is a term used to describe the sloping section of coast between the top of the cliff and the beach. It is characterised by landslides that slowly, but continually move, giving rise to a rich mosaic of habitats.
Age: recently active from 20,000 years ago to the present day
Where to go: The Axemouth to Lymw Regis Undercliffs can only be accessed using the Saouthwest Coast Path. It is 7 mile stretch of rugged path that is difficult in places.
Look out for: Spectacular wildlife – wild woodland, nesting Peregrine Falcons and Ravens as well as various wild flowers and insects.
The torn land between the fields and the sea
The huge landslides that occur between Lyme Regis and Axemouth happen because of the geology. Chalk and sandstone above sit on clay and limestone below. The chalk and sandstone absorb water like a sponge, becoming very heavy, and move across the impermeable and slippery surface of the clay beneath. This often happens slowly, pushing rock and soil before it, causing breaks in the established paths and pushing trees over. Occasionally it happens in spectacular fashion as it did in 1839 When Goat Island was formed.
The Bindon Landslide of 1839 was a famous event at the time. One night, a huge slab of land, known locally as goat Island, moved towards the sea and a large chasm opened up behind it. The front of the landslide was lifted up out of the sea creating a small natural harbour, although this was quickly eroded away. Today, Goat Island and the chasm are two of the most noteworthy features within the Undercliffs.
The National Nature Reserve is managed by Natural England to preserve and protect the amazing wildlife that lives there.
Location: between Beer and Branscombe, East Devon.
Landform Type: Landslide in Chalk.
Age: formed in 1789
Where to go: Hooken landslide is a short walk west from Beer. Sturdy footwear and great care is needed when attempting the footpath down through the landslide. Beer is on the X53 bus route.
Look out for: Peregrines perched on top of Chalk pinnacles, the nationally rare 'Purple Gromwell' plant and evidence for coppiced ash trees that pre-date the landslide.
A deep landslide
Hooken landslide occurred because the here Chalk sits on top of slippery clays from the Triassic period. These are buried deep under ground but it is here that the rocks gave way, causing the dramatic landslide above. Today the landslide is relatively stable and a well established path runs through it.
Budleigh Salterton Beach – Pebbles from the past
Location: Budleigh Salterton, East Devon
Landform Type: Large pebble beach
Age: Formed some time in the last 10,000 years, after the last ice age
Where to go: Budleigh Salterton is on the main bus route between Sidmouth and Exmouth and is easily reached by car.
Look out for: Pink pebbles – these uniquely coloured pebbles only come from this beach and nowhere else in the UK. Removing any comes with a fine of up to £2000!
Pebbles from the past
All the pebbles that form the ebach at Budleigh Salterton come straight out of the cliff. There is a lyer of rock here made up of these pebbles and is known as the 'Budleigh Salterton Pebble Bed'. The pebbles were once carried by a river nearly 250 million years ago before being deposited and buried. Now they are eroded out of the cliff to form the beach. They are made of a very hard rock known as quartzite.
This beach is special because it allows scientists to investigate, in detail, the relationship between the supply of pebbles and the size and nature of the beach they make up. It is also free of any major coast defences and so lets us study how a beach behaves naturally, without being interfered with by human beings.
Location: Ladram Bay, East Devon
Landform Type: Naturally formed sea stacks
Age: Triassic, 245 - 235 million years old
Where to go: You can get to Ladram bay by foot along the south West Coast Path or by car via the Ladram Bay Holiday Park.
Look out for: Sea birds on the rock stacks.
Resisting the Sea
The cliffs and stacks at Ladram Bay are made up a red coloured soft sandstone that formed in deserts during the Triassic period. The layers of sandstone are harder in some places than others. These harder areas resist erosion from the sea whilst the softer rock is worn away around them. Eventually the harder parts of the sandstone stand entirely free of the cliffs – these are known as sea stacks.