Geography Trip to Dorset

Currently we’re studying coasts in Geography, ready for our exam which will be in May. As part of this, yesterday we went down to Dorset for the day.

We arrived shortly after midday after a nearly 3 hour coach journey from college. Our first stop was Chesil Beach, which is 18m/28km long and runs from near West Bay to the Isle of Portland – with the beach formation being the only thing connecting Portland to the mainland (and if you want to be really clever, its the A354 which is built over the top of it).

It is a pebble and shingle tombolo connecting Portland to Abbotsbury and then continuing north-westwards to West Bay near Bridport. It is the largest tombolo in the UK.

Quoted from ChesilBeach.org

So… how was it formed? Well, it appears to be something which the experts are still arguing over. However what most experts seem to have agreed on is the fact that it was formed due to sea level rise. This formation started about 20000 years ago. Sediment from the sea bed was pushed up to form the tombolo.

Chesil Beach is unique because it has the Sea on both sides. One website suggests that it stabalised close to where it is now about 5000 years ago, and is now moving at towards the East about 15cm/year towards the South – and slower towards the North.

When we arrived yesterday, we found it was very windy… and that was when we got off the coach. We then had to climb the mountain of pebbles to the top of the beach, where we felt the full force of the wind – trying to write down notes was very hads with red hands, and not being able to hear a thing because my waterproof made so much noise in the wind.

You must remember that Chesil Beach isn’t exactly the sort of place you’d want to swim (or even paddle) at, even when the weather is at its calmest:

  • The seaward side of the beach is a wave-swept environment that changes at every storm. The pebbles are generally very unstable and whilst it is easy to go down the beach to the shore, getting back up can be a physical challenge.
  • Do not venture close to the shore line. Even in calm conditions large waves can suddenly appear. The shoreline of the beach is very steep and this can result in a very strong undertow under some wave conditions. We strongly recommend that you do not swim off the beach.

Quoted from ChesilBeach.org/Safety.html

The waves were massive yesterday,although my teacher has said she’s been there in worse conditions. Looking at a map, its not hard to see why all the waves are so massive and the wind so strong:

Dorset

Chesil Beach on the map above (which has been taken from the BBC Dorset website) is basically the straightest line on the map, running from just West of Lyme Regis, all the way down to Portland.

If you were stood on the beach looking out to sea, you’d be facing South West. In other words, straight in to the dominant prevailing winds that we get here in the UK. The waves approach the beach from almost a straight angle.

We stayed at Chesil Beach for half an hour, where we measured some pebbles at two locations – both were within half a mile of each other – but we found that even in that space on the 18m long beach the size of the pebbles changed dramatically.

The obvious answer to this would be longshore drift. You’d expect that the larger pebbles would be at the West Bay end, getting smaller as the tide carries them towards Portland. But the largest pebbles were in the South Eastern corner of the island, and longshore drift happens from West to East.

In the afternoon, we went further East to Lulworth Cove (near the village of West Lulworth). The waves weren’t so big there – thats because Chesil Beach/the Isle of Portland shelters it a bit. On the map above, its probably around where the “y” is.

We had lunch at a little fish & chip place in the carpark, and then went to look at the geography of the area.

The cove has formed because there are bands of rock of alternating resistance running parallel to the shore (a concordant coastline). On the seaward side the clays and sands have been eroded away. A narrow (less than 30 metre) band of Portland limestone rocks forms the shoreline. Behind this is a narrow (less than 50 metre) band of slightly less resistant Purbeck limestone. Behind this are 300-350 metres of much less resistant clays and greensands (Wealden clays, Gault and Upper Greensand).

Forming the back of the cove is a 250 metre wide band of chalk, which is considerably more resistant than the clays and sands, but less resistant than the limestones. The entrance to the cove is a narrow gap in the limestone bands. This was formed by a combination of erosional processes by wave action , glacial melt waters and the processes of weathering. The wide part of the cove is where the weak clays and greensands have been eroded. The back of the cove is the chalk, which the sea has been unable to erode as fast.

Quoted from Wikipedia

As we discussed the geography of the area, we were stood on the footpath with the cove on one side, and Stair Hole on the other. Stair Hole is a smaller version of Lulworth Cove, probably what it would have been like a few hundred thousand years ago.


In a few hundred thousand years it may be as large as nearby Lulworth Cove. The folded limestone strata known as the Lulworth crumple are particularly visible at Stair Hole.

Quoted from Wikipedia

After studying/discussing Lulworth Cove and Stair Hole for a few minutes, we headed back through the car park, and towards the coastal footpath. At first, I was doing OK… but as the path (a mountain) got steeper I slowed down considerably. I was the last but one to make it to the top… where it was very windy again. By this time, I was out of breath. Anyone would think that I’m unfit and don’t do any form of sport or excersise…. 😛

We were heading towards another interesting geography feature: Durdle Door.

Durdle Door

The arch has formed on a concordant coastline where bands of rock run parallel to the shoreline. Here the rock strata are nearly vertical, and the bands of rock are quite narrow. Originally a band of resistant Portland limestone ran along the shore, the same band which can be seen one mile down the coast forming the narrow entrance to Lulworth Cove. Behind this is a 400-foot (120 m) band of weaker rocks which are easily eroded, and behind this is a stronger and much thicker band of chalk, which forms the Purbeck Hills. The limestone and chalk are much closer together here than at Swanage, 10 miles (16 km) to the east, where the distance between them is over 2 miles (3 km).

Quoted from Wikipedia

After that, we walked back up the mountain, and then (for some reason) through a caravan park in order to get to the main road where the coach picked us up. Presumably, that was so we didn’t have to climb back up the mountain to get back to Lulworth Cove, but as far as I could tell, we still had to climb up the mountain to get to the main road anyway! 😐

I enjoyed the trip (there wasn’t much writing to do) and it was good to get out of the classroom for a change. We returned home shortly after 1940 yesterday evening.

One more thing, whilst I’m thinking about coasts: If Mum or Dad are reading this, can we have another holiday soon please? We haven’t been to either Cornwall, Dorset or Wales for a while now. 😀

After all, the British coastline is (in my opinion) the most interesting in this part of the world.

Fred Hart

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