Originally the estuary was open to the sea allowing Helston to be a sea port. However, by the 13th century the formation of the bar had caused the entrance to become blocked and the formation of the freshwater pool.
In very simplistic terms it has been created by "a spit forming on one side by the process of longshore drift which has extended across an inlet sealing it off and trapping a lagoon behind it".
Longshore Drift Simple Theory: When waves hit a beach or coast at an angle their energy pushes material up the beach at that same angle. When the wave retreats back down to the sea it drags material at 90 degrees to the shore. When the next wave hits the process is again repeated. Material such as sand, shingle and rocks are therefore moved in a zig-zag pattern along the beach and this is what is known as Longshore Drift.
Currently there are several other theories to explain the formation of the Bar. It is thought that the initial feature could have been put in place as a result of the Post Glacial rise in sea level. Sea level was possibly over 100 metres below its present level during the peak of the last Ice Age. Ice sheets covering much of the U.K. had eroded millions of tonnes of material as they moved over the landscape. This was deposited as they melted forming huge areas of deposition. This material became incorporated into the beaches of the landmass surrounding the U.K. As sea level rose to its present level the beaches moved with it until they reached their present position about 6,000 years ago (this wasn't a rapid movement in human terms - perhaps 1cm. a year). Several areas of coastline then found themselves with shingle features in front of them. This included the blocking of several valleys in Cornwall and South West England.
Although this may have formed the original feature other processes and factors have definitely modified it. The Bar was much smaller than it is at present and was not such a stable, permanent feature that it is today. Up until the 1850's it was probably half the width it is now and much lower. This was not helped by its continual breaking to let floodwater out during the winter months. Local estate workers were employed to dig a channel across the bar to lower the water and stop the houses of St John`s, Helston being flooded.
The mining in the valley had also made this worse by the very large quantities of fine mineral waste being discharged by the mines into the River Cober blocking the pore spaces in the shingle Bar. This greatly reduced the Infiltration Capacity of the shingle in the Bar, making the size and number of flood events much greater.
So what turned the Bar into its current size and shape?
Longshore drift plays a role in this - there are very large movements across the face of the Bar. Thousands of tonnes can be moved on and off the Bar front in just a few hours during violent storms as Longshore Drift operates in both directions across the Bar.
Large storms and tidal waves have probably played a major role since the 1850's. Tidal waves hit the Cornish coast in June and October 1859 and in April 1868. These events were not part of any storm and were not just simply one huge wave - the one in 1868 was described as being a "succession of hundreds of great waves for more than an hour". In January 1924 another tidal wave destroyed part of the fishing village of Porthleven, swept away large areas of the cliff and threw vast quantities of shingle onto and over the Bar.
Large storms have continued to deposit hundreds of tonnes of shingle onto and over the Bar in recent years. The enormous waves produced by these storms have not destroyed the Bar but have been very important in building up and stabilising the feature. The bar is often overtopped by waves in these storms - a frightening prospect when you're standing on the Bar and imagining the size of the waves.
PLEASE NOTE: I CANNOT ACCEPT JOINT ANSWERS FROM GROUPS OF GEOCACHERS NOR JOINT PHOTOS AS I DON'T HAVE THE TIME TO SORT OUT WHO HAS SENT WHAT FOR WHOM!. IF YOU WANT TO LOG MY EARTHCACHE PLEASE EXTEND ME THE COURTESY OF SENDING ME YOUR OWN ANSWERS INDIVIDUALLY AND ADD A PHOTO TO YOUR OWN LOG (optional). THANK YOU
To log your visit you must complete a task:
1. Visit the Loe Bar at any tide state and take at least one photo (optional)of the Bar from the northern (Porthleven) side with your GPSr in the foreground and upload this to your log entry. If you would like to be in the photo that would be great.
2. MESSAGE me the answers to the following questions. You can contact me via the LINK at the top of this page. Do not put the answer on the `logged it` page
a. Estimate the Loe Bar dimensions - length, width and maximum height. Metric or Imperial is acceptable.
c. Loe Pool would flood the town of Helston if it`s water could not escape to the sea. Suggest two ways in which the freshwater escapes: One Man Induced and one Natural!
Have fun exploring. Take a picnic and enjoy the beautiful scenery. However, DO NOT SWIM in either Loe Pool or the sea off the bar as it is very very dangerous. Good luck!
YOU MUST LOG AT THE SAME TIME AS SENDING ME YOUR ANSWERS VIA A GEOCACHING MESSAGE. If you can`t do both at the same time then wait until you can, otherwise I will just delete your LOG and you will have to do it all again as I DO NOT have the time to chase after you. AND be warned, I do check every one! Unfortunately, a few geocacher`s try to log the earthcache without completing the task and so I will maintain the right as the earthcache owner to delete any logs that do not fulfill the requirements or I entries that I believe to be false. I will ONLY contact you if there is a problem AND I will delete any logs for which I don`t receive answers or LOGS that I believe to be false.
This is No 2 in Snake Plissken`s Lizard Peninsula Earthcache Series!
SNAKE PLISSKEN -