CHAPTER 10: COASTAL PROCESSES, PATTERNS AND LANDFORMS 10.3 Marine processes
Processes of marine erosion The sea erodes the coastline in several ways. Hydraulic action
The crushing force of tonnes of water in each wave wears the land away. The pressure exerted by Atlantic waves in winter average nearly 10,000 kg/m2
. Hydraulic action is
most effective on soft coastlines such as Louth, Dublin and Wexford. Abrasion
Waves throw stones and sand against the coast wearing it away. Abrasion is most effective at high tide and during storms. Air compression
As waves break against the coast, air is trapped and compressed in small crevices in rocks. When the wave moves away, the air is released. This expansion and compression shatters rock.
Attrition
The load carried by the waves is itself worn down by constant rolling and knocking together. This is why beach cobbles are usually well rounded. Ultimately, sand is formed in this way.
Solution
Salts in sea water can dissolve rock by chemical means. Chalk and limestone coasts are most easily eroded this way.
Processes of marine deposition Deposition occurs when the sea loses its energy. Waves, tides and local currents combine to drop sand and shingle at particular locations.
The conditions required for deposition are: 1. Gently sloping beaches which reduce wave energy. 2. Shelter from strong winds and currents creating calmer seas. 3. Constructive waves allowing sand to settle on the beach.
Many bays and inlets have these conditions, allowing beaches and other depositional features to form there.
Processes of marine transport
Huge amounts of material are carried along our coastlines each day. Waves and currents are constantly moving sand along the coast due to a process called longshore drift. Longshore drift (littoral drift)
This is the movement of material along the coast. It occurs because the coastline is irregular and waves do not break parallel to the coast (wave refraction). The swash moves sediment up the shore at an angle and the backwash pulls the sediment back out to sea at a right angle to the shore.