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15th May 2021 - Ranger Daves Brief Geological History of the Solent

This week we have another special guest blog, written by Dave, one of our brilliant Rangers from the 2020/2021 winter season! While he was with us, he wanted to discover more about the geological history of the area we work in - the Solent, and as we are now celebrating #SolentMonth during May - this seemed the perfect time to share how he got on...

Most of us who live and work on the south coast are very familiar with the geography of the Solent, but its coastline hasn't always looked like it does today; the story of how it came to be that way is quite a dramatic geological tale.

Firstly, a little background to the history of the English Channel - it hasn't always been there; at least, not the sea that we know. Almost half a million years ago, there began a series of ice ages which lasted until around 12,000BP (Before Present years, a standard timescale used in geology). During an ice age, large amounts of the world's sea water is "locked up" in continental glaciers, causing global sea levels to fall, sometimes dramatically - at various times during these glacial periods the sea level was as much as 140m lower than at present. The British Isles were part of a contiguous European landmass above sea level, and what is now the English Channel seabed was dry land; it would have been possible to walk to France.

2021_05_15 Dave Solent 1

 

Recent geological findings indicate that the English Channel originated from a "megaflood" event, whereby a massive dammed lake formed by glaciation breached the chalk ridge between modern day Britain and France (known to geologists as the Weald-Artois Anticline), forming the Strait of Dover; the famous white cliffs of Dover are a remnant of this ridge. The force of the flood carved a wide channel which became known as the Channel River, which flowed into the Atlantic and is thus  believed to be the first separation of Britain and the rest of Europe.

 

2021_05_15 Dave Solent Needles 2 The Solent itself began life as another large river fed by several tributaries, and outflowing to the Channel River, as shown in this hypothetical map of the Solent river and coastline at the end of the last ice age, around 12,000 years ago.

The black dotted line on the map shows the line of the chalk ridge that ran between the Needles and Handfast Point, north of Swanage (the Wight-Purbeck Ridge). This was the last land link between the Isle of Wight and mainland England, remnants of which are of course still visible today.

 

2021_05_15 Dave Solent Fort

 

As the last ice age ended, several forces combined to create the Solent we know today: melting ice caused sea and river levels to rise, which in turn led to their widening and deepening through erosion; at the same time, the loss of the tremendous weight of ice over northern Britain led to a geological effect known as isostatic rebound, whereby northern Britain is slowly rising while the south is slowly sinking - a process still happening today. These effects combined to slowly inundate the Solent and form the harbours of Portsmouth, Langstone, Chichester and Pagham as well as Southampton Water. Eventually, probably around 7,500 years ago, the Wight-Purbeck Ridge was breached, connecting the western Solent with the English Channel and finally disconnecting the Isle of Wight from the mainland. This map helps to visualise how the coastline of Europe changed as sea levels rose.

Of course, geological and climatic forces are constantly at work - with global sea levels predicted to keep rising, the Solent coastline will continue to change, with consequences for both its human and wildlife inhabitants. Who knows what it will look like even a hundred years from now!

Note: The above is a very simplified version of events, but if it has piqued your interest in going into the subject in greater depth, here are some excellent sources which provided much of the information presented here:

SCOPAC - Quaternary history of the Solent

2021_05_15 Ringed Plover

Video: Dr. Jenny Collier, Imperial College: Megaflood - how Britain became an island

Ian West: Introduction to Solent Estuaries

National Geographic: Doggerland - the Europe that was

P.S. I hope you found this blog interesting. I really enjoyed learning about the Solent and its wildlife over the winter, but like our wintering birds, I have now migrated North! I can currently be found working for the National Trust in Northumberland at their Beadnell Bay site, helping to protect breeding colonies of Little Terns, Arctic Terns and Ringed Plovers.

Ranger Dave