A beach is usually a gently sloping, flat strip of land that normally lies along (or near to) an ocean, river, or lake. Beach materials include pebbles, sands, rocks, and other sea-related debris that accumulate on beaches over time. Most natural beach materials have been exposed to weathering and erosion over time. Many types of beach deposits have been formed in response to continental movements and can take a very long time to form.
Beach erosion occurs when a beach surface is influenced by the movements of underlying water – most often the ocean. The gradual movement of waves and currents, combined with wind, can wash away layers of beach material over time. This leads to differences in thickness – the depth of individual layers can vary by hundreds of meters or even thousands of feet!
Beach nourishment occurs when sediment naturally washed away by the tide builds up behind it. As the sediment compacts, layers of sand and shells settle to the bottom. Over the years this becomes very effective in protecting the beach from erosion. Sand and shells do not provide the same level of protection as bedding, but they do form barriers that keep out stronger winds and force the waves to go over smaller beds of sediment at the base of the beach.
Beneath these layers of silt and sand lie minerals that form a structure known as a beach deposit. These minerals range from fine grains of sand, through to coarse crushed stones or boulders. These fine grains or sand are often black or blue in colour thanks to chemical reactions during the slow oxidation process that takes place below them. This creates a beautiful aesthetic appearance that blends in perfectly with surrounding sea life and plants. In some parts of the world, different kinds of sedimentary rock can be found in different colours. It is during the process of metamorphosis that rock minerals combine to create unique pigments such as blue or black.
Another problem that can occur at beaches is erosion due to heavy minerals. As sea levels rise and retreat, coastal areas can experience steep slopes and erosion can take place. At the higher elevations, steep slopes become more common as water flows over the area. This process is called longshore drift and can lead to damage to the beach as well as disrupting the view.
Longshore drift can be prevented to some extent by preventing beach development on eroding slopes. In areas where slopes have been eroding for many years beaches can be rebuilt following high tide, although the process can be hard due to the combined effects of erosion and waves. At certain times of the year, especially when it is unlikely to see much development, the use of tide pools can be extremely useful.