June 06 Past Paper

June 06 Past Paper 2. a. i) Constructive Wave A constructive wave is a wave that is less than 1m in wave height and has a wave length of up to 100m. It has a stronger swash than backwash and therefore deposits material on beaches. It has a long wave period and a low wave speed. Destructive Wave A destructive wave is a wave that is normally upwards of 1m in height with a wave length of less than 20m. It has a stronger backwash than swash and therefore takes material away from beaches. It has a short wave period and a high wave speed. ii) As a wave approaches a shore its wave base will touch the shallowest ocean floor first, this increases friction on that side, slows the wave down and makes it turn that way until the wave is parallel to the ocean floor, and parallel with the shore. This can be shown in a diagram by using orthagonals which are lines showing equal wave energy. Wave refraction makes sure that waves break parallel to the shore and it can focus the waves onto headlands. See diagram. b. i) Sand dunes along this stretch of the coast are dituated on spits only. Specifically the two largest spits which are the two off Aber Dyfi ad off Aber Mawddach. Estuarine sands and salt marshes are situated in very much the same places. Around the spits though there is a small amount of Estuarine sand around the Aber Dysynni spit and the Aber Artro area. ii) A spit is a landform formed by marine deposition. A spit is formed when longshore drift, which is the movement of material along a coast by waves, gets to a sudden change in sea depth (normally around an estuary). This means that the waves loose energy and the material is deposited next to the shore. Over years enough material is deposited so that it protrudes above sea level. This is the proximal end of the spit, as more material is deposited by longshore drift moving it along the spit moves out across the estuary until it gets to a point where the estuary current doesn’t allow it to deposit anymore and this is known as the distal end. At the distal end there may be a recurved end where a change in wind direction has caused the longshore drift to change direction and material to be deposited in a new direction curving the

end of the spit. There may be several recurved sections of a spit. A spit itself is a long stretch of sand stretching partly across and estuary, the part closest to the shore is called the proximal end while the part furthest away is called the distal end. There may be part of the spit that curves back on itself and this is called the recurved end. On top of the spit there may be sand dunes and behind the spit there may be a salt marsh. c. i) Eustatic sea level change is the change in sea level due to the amount of water in the oceans being changed, i.e. the water level may increase as the ice caps melt or decrease as ice caps or glaciers form. As ice caps melt water is added to the ocean and this increases the sea level. As ice caps form water is removed from the ocean and the sea level decreases. ii) Millions of years ago England was covered in glaciers and huge ice caps. This slowly depressed England and lowered its level in relation to the sea. Of course the land was pushing up against the ice caps. As the ice melted the land kept pushing up. Particularly in the North-West of England. Today the North-West of England is still pushing up against the ice-caps that aren’t there anymore, resulting in a rise of its altitude above sea level. However, this has a pivot effect on the Southeast of England and is causing it to lower itself, making the sea-level slowly rise around its shores. iii) Coral reefs are formed nearly always between the Tropic of Cancer and the Tropic of Capricorn. In this area water temperature is relatively warm (20-30oC) and constant. There is also an increase in the amount of sunlight in this area. Coral reefs form between 1 and 20m below sea-level normally, though they can form below this depth. An example of this is the Great Barrier reef in Northern Australia. A type of coral reef is the atoll. An atoll is formed by a fringing reef forming around an island. As the sea level rises it leaves the island behind, but the coral keeps increasing upwards. This leaves a ring of coral islands around a circle of water, or lagoon. This is an Atoll.