North Beach Dunes EarthCache
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The Norfolk coastline is dominated by erosional or destructive processes acting negatively on the landforms but as every action has a reaction I thought I would highlight an area where depositional or constructive processes are in action.
The coastline is the place where land meets sea. Weathering helps to break up the rocks exposed along the coast while waves, generated far out at sea, erode the rocks to create familiar landforms such as cliffs and caves. Eroded rock particles, reduced to sand and mud, are transported along the coast by waves and currents. Eventually these particles are deposited elsewhere to form new features such as beaches, sand dunes and salt marshes.
Longshore Transport
When waves arrive at the coast indirectly, they move sand and shingle along beaches, rather than up and down them. This process is called longshore drift. Because waves strike the coast at an oblique angle, the swash follows the same angle up the beach, carrying sand and shingle with it. However, the backwash returns down the beach on a straight path, at right angles to the shore. This means that each wave produces a saw-tooth movement of swash and backwash. As a result, sediments are shifted in a particular direction along the beach. While this beach drift is going on, the oblique angle of the waves produces a longshore current. This flows parallel to the shore, and transports large amounts of sand along the coast. Deposition of sand and shingle by waves and currents is responsible for distinctive landforms on constructive, lowland coasts, especially beaches and spits.
History
This area of coastline has changed dramatically since the OS map produced 1886 was published, luckily the train line has given me a reference point to measure the distance to the low tide mark and as you can see this was 310m
OS MAP 1886
The aerial photo taken in 1946 shows the distance measured from the same point has grown to 450m, there is no way of finding out the state of the tide at this point but it can be said the beach has grown by at least 140m in 60 years.
AERIAL VIEW 1946
The final aerial phone taken in 1988 shows a vast increase in the size of beach and dunes.
AERIAL VIEW 1988
Sand Dune Formation
Sand dunes are sometimes found at the top of beaches, above the high tide mark, but not every beach has dunes. For dunes to form there must be a supply of sand, a means of transporting it, and somewhere for it to be deposited more quickly than it is eroded. When the dried sand reaches the top of the beach it can be trapped by debris such as driftwood, dead seaweed or rocks and pebbles. If the sand is not eroded again it may become colonised by small plants, or trap other windblown debris, increasing its size and thus trapping even more sand. At low tide, deposits of sand in the inter-tidal zone may be exposed and start to dry. The dry grains of sand can then be transported by the wind. If the wind blows towards the land, sand will be transported up the beach and beyond the high tide mark. As the dunes grow in size they are able to catch more of the sand blown across them by the wind. Thick covering of vegetation preserves the dune in two ways. Firstly the roots bind the sand together, and secondly the above ground vegetation traps particles of sand as they are blown over the surface.
To Log The Cache
Start at trailhead 1 (coordinates given in additional waypoints) this is the centre of the bridge over where the train line once stood, from here walk towards the beach and carry on until you reach the edge of the sea. The answers to the following questions should be sent to me using the ‘send message’ function on my profile page.
What is the distance in metres between trailhead 1 and the edge of the sea?
What are your coordinates at this point?
What is the wind direction?
Referring to the information provided on sand dune formation, describe what is happening at the time of your visit regarding the wind?
How far, in time are you from the nearest low tide and is the tide going in or out?
If possible please provide pictures of your visit but this is not a requirement of logging the cache.
Additional Hints
(No hints available.)