Poole Harbour Earthcache EarthCache
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Poole Harbour is the largest natural harbour in Europe and the second largest natural harbour in the world.
Please note: If you're making a special journey to this Earthcache, check the ferry status via their Twitter feed @SandbanksFerry
“The harbour is a drowned valley formed at the end of the last ice age and is the estuary of several rivers, the largest being the Frome. The harbour has a long history of human settlement stretching to pre-Roman times. The harbour is extremely shallow (average depth: 48cm), with one main dredged channel through the harbour, from the mouth to Holes Bay in Poole. Once a major port, freight transport has declined, but the port still takes regular cross-Channel passenger ferries.” Wiki
"The harbour is in a band of weak gravel and clay which is easily eroded by the rivers and sea. This band is bordered by two bands of chalk, the Purbeck Hills and Isle of Wight to the south, and the Dorset Downs and South Downs to the north. The clay extends west up the Frome valley to Dorchester, and would originally have extended east beyond Portsmouth in Hampshire. Before the last ice age the River Frome continued to flow east through what is now the Solent, joining the Stour, Beaulieu, Test, Itchen and Hamble, before flowing into the English Channel to the east of the present day Isle of Wight. A relatively resistant chalk ridge ran continuously from the Purbeck Hills to the Isle of Wight, which the rivers could not break through. When the glaciers of the north of the island of Great Britain melted, the south of England sank slightly, flooding the Solent valley and Southampton Water to form their characteristic rias (flooded estuaries). About 7,000 years ago, increased erosion from the sea and the increased flow caused by the change in climate broke through the chalk hills, cutting the Isle of Wight off from the Isle of Purbeck and flooding what is now the Solent and Christchurch Bay, leaving Poole Harbour as the estuary of the Frome." Wiki
The harbour is the site of the largest onshore oilfield in Europe. There are three major oil reservoirs that lay under Poole Harbour and Poole Bay. The Bridport reservoir is 900 metres below the surface and lies above the Sherwood reservoir, which extends eastwards under Poole Bay at a depth of 1600 metres. Further exploration discovered the 7.5 million barrel Frome reservoir in clay/limestone at 750 metres.
The harbour is an area of Outstanding Natural Beauty featuring
• Sites of Special Scientific Interest (SSSI).
• Special Protection Areas.
• World Heritage Coastline.
• Ramsar sites (designated wetlands of international importance, as agreed at Ramsar, Iran, 1971).
• National Trust land
• National Nature Reserves
The harbour entrance at 300m wide is the most hazardous area of the harbour with very strong tidal streams particularly at spring ebb and a slow moving chain ferry operates at its narrowest point.
There are a number of islands and beaches in the harbour and its’ shallow depth makes it perfect for water sports enthusiasts.
Useful Links:
Live Poole Harbour weather, updated every three seconds
Poole Harbour webcam
To log this earthcache, it is necessary to visit the harbour entrance, (co-ords given are for the north side, but south side equally acceptable).
1.You need to have your photograph taken (holding your gpsr) with the Sandbanks Ferry in the background OR Locate the steps near the GZ co-ordinates and take a photo showing the height of the water on the steps and comment on the state of the tide at the time you took the photograph.
2. Time the journey of the chain ferry and use this to estimate the speed it is travelling at. State why this may vary from time to time. (N.B. Boat traffic is not the answer I am seeking).
3.You also need to email the cache owner with the name of the oilfield in Poole Harbour and also the names of the 8 largest islands.
Please only post your photo and NOT your answers here, email the cache owner.
Logs without the required email answers and photo will be deleted within one month.
The harbour entrance is a busy waterway, the ferry runs on chains which come onto the slipway, you are advised to supervise children and keep dogs on a lead in this area.
Please ensure that you send me the answers and upload your photographic evidence within 48 hours of logging this cache - unless prior permission has been granted by me, your log will be removed, without further reference to you thereafter. No retrospective logging of this earthcache please.
Additional Hints
(Decrypt)
Gur uneobhe ragenapr vf ng Fnaqonaxf.