In this Earthcache you are going to observe the local tides and discover their effect on access to the island of Lindisfarne.
Lindisfarne is the archaic Anglo-Saxon name for Holy Island. Situated off the east coast of Northumberland, the island is about 3 miles long and a little over a mile wide at most, but with a rich history of well over a thousand years. I can thoroughly recommend a visit to this special island - more information can be found here - but be sure not to be caught by the tide as you cross! It does happen; my thanks to angellica for spotting this story.
Image produced from the Ordnance Survey Get-a-map service. Image reproduced with kind
permission of Ordnance Survey and Ordnance Survey of Northern Ireland.
Visible to the south of the causeway, a series of tall posts mark an alternative pedestrian route to the island, known as the Pilgrims' Way. More adventerous cachers may choose to take this route but extra care is required and it should be noted that it is not recommend unless you have local knowledge. In particular, this foot crossing should never be attempted at dusk or on a rising tide! Safe times for the Pilgrim's Way are not published and, as with the causeway, current meterological conditions may significantly shorten the safe crossing period.
Tides are caused by the gravitational attraction of the Moon pulling the water "up". This results in a bulge in sea level on the side of the Earth facing the Moon. A similar but opposite bulge is observed on the far side of the Earth where the effect of the Moon's gravity is lowest. As the Earth spins on its axis, the bulge stays lined up with the position of the Moon, causing the regularly changing sea levels that we observe as tides. The Sun has a similar but smaller effect on the seas leading to variation in tide height throughout the lunar month.
To claim this Earthcache, you are going to record a number of observations regarding tidal conditions on the causeway. The Earthcache waypoint refers to parking at the western (mainland) end of the causeway. From this point, or nearby, safe observations of parts 1 to 5a are possible. If, and only if, tidal conditions are safe, part 5b may be undertaken. However, you should be warned that if you choose to cross towards the end of the safe crossing period you may find yourself stuck on the island for 6 hours or longer!
1) Record the time of your visit.
2) Record whether the causeway is passable at the time of your visit.
3) Optional task:If possible, take a photo of yourself and/or your GPS showing the tidal conditions at the time of your visit.
4) Find the local tide tables and record the safe crossing times for the date of your visit.
5a) If the tide is in:Tide times get later as you move South along this part of the coast, implying a general Southward current. However, local flow is likely to be influenced by the shape of the island, weather conditions on the day and state of the tide. Record the direction of flow of water in the channel between the mainland and the island, the direction and approximate strength of the wind and whether you are observing an ebbing (falling) or flowing (rising) tide.
Record all the above data in your log
5b) If the tide is out:Drive (or walk...) to the far end of the tidal causeway. This won't be where the road first hits the island! Measure or estimate the total length of the causeway. DO NOT RECORD THIS INFORMATION IN YOUR ON-LINE LOG.
6) It may be that the day you visit has only one safe crossing period listed. If not, check the tide tables to find a date when this occurs. By using tide data from adjacent dates, can you explain this phenomenon? DO NOT RECORD THIS INFORMATION IN YOUR ON-LINE LOG.
Don't forget to include your observations for tasks 1 to 5a in your log and enjoy your visit to Holy Island. Answers to 5b and 6 should be emailed to me. Please note that I am unlikely to respond to your email unless you check "I want to send my email address along with this message". Please do NOT use the awful Messaging Centre system to contact me.
Above all else, obey the warning signs and stay dry!