Coastal Landscapes Booklet 2 PDF

# Coastal Landscapes and Change ## Booklet 2 - **Wavelength** - the distance between two successive crests - **Wave frequency** - the number of waves per minute - **Wave crest** - the highest point of the wave - **Wave trough** - the lowest point of the wave - **Wave steepness** - the ratio betwe...

# Coastal Landscapes and Change ## Booklet 2 - **Wavelength** - the distance between two successive crests - **Wave frequency** - the number of waves per minute - **Wave crest** - the highest point of the wave - **Wave trough** - the lowest point of the wave - **Wave steepness** - the ratio between wave height and length (waves break at 1:7) - **Wave period** - the time taken for a wave to travel one wavelength across water - **Fetch** - the uninterrupted distance over which wind blows (building waves) **Waves directly influence coastal erosion transportation and deposition leading to the shape of the coastline.** - **Waves** are created by transference of energy from wind over the sea surface. - **Waves** are simply energy moving through the water. **The size and energy of waves depend on:** - Strength of the wind - Wave fetch - Water depth - Direction wind blows for **Swell** - Waves that come from storms out at sea. - Waves that come when its still weather at the beach. - **Less steep** - **Longer period** **Waves break because the crest moves faster than the trough.** - The water that goes up the beach is the **swash** - The water that runs back is the **backwash**. **Constructive Waves** - Low wave height - Long wave length - Strong swash - Pushes sediment up the beach - Creating a berm - Weak backwash. **Destructive Waves** - Big wave height - Short wavelength - Strong backwash - Pulls sediment off the beach, this then collides with the south and loses energy depositing a sand bar. **Beach Morphology:** The shape including width, slope and features such as berms, ridges and runnels. Also includes the type of sediment. **Different Types of Beaches** - **Storm beaches** result from high energy deposition of course sediment in severe storms - **Berms** formed from shingle and gravel result from constructive deposition. - **Offshore ridges/berms** formed from destructive wave erosion and subsequent deposition of sand shingle offshore. **Tides** - Tides are short term changes caused by gravittinal pull of moon and sun - Roughly every 12 hours. - The moon puts water towards it, then there is a compensatory bulge at the other side of the earth. - In between the 2 bulges is low tide **Coastal Processes** **Marine Processes:** Processes operating upon a coastline that are connected to the sea, such as cove, tidy and longshare drift. **Terrestrial Processes:** Processes operating on land but affect the shape of the coastline, such as weathering, mass movement and erosion - marine fun off. **Hydraulic Action** - When water is tripped in cracks in the rock by forcing it in, breaking the rock more. - Sedimentary rock very vulnerable - Lots of credenesssey - Joints, bedding plains etc... **Abrasion** - When sediment being carried by the water hits the cliff acting as an abrasive (like sandpaper) . - Needs loose sediment. - Sedimentary rock vulnerable. **Solution (Corrosion)** - Chemicals in the water dissolve the rock. - Mainly effects limestone. **Attrition** - Rocks being carried by the water hitting together ends getting smaller, makes pebbles smaller and rounder. **Weathering - terrestrial** **Weathering** - gradual breakdown of rock on the ground surface. - **Mechanical (Freeze Thaw):** The fracture and brellon of rock into fragments. Salt crystallisation. - **Chemical:** Decomposition of rocks, changing minerals in the rock, weakens the cliff. Limestone vulnerable. - **Biological:** When plants and animals burrow or grow roots into the rock, opening cracks for hydraulic action. **Mass Movement**: The movement of weathered material downslope due to gravity. | **Type** | **Process** | **Explanation** | **Vulnerable rocks** | |---|---|---|---| | **Mechanical**| **Freeze-thaw** | Water expands by 9% in volume when freezing, exerting a force within cracks and fissures; repeated cycles force cracks open and loosen rocks. | Any rocks with cracks and fissures, especially high up cliffs away from salt spray. Freezing is relatively uncommon on UK coasts, especially in the south, and salt spray can reduce its effect even further. | | **Salt crystallisation** | The growth of salt crystals in cracks and pore spaces can exert a breaking force, although less than for freeze-thaw. | Porous and fractured rocks, for example sandstone. The effect is greater in hotter, drier climates where evaporation and the precipitation of salt crystals in more pronounced. | | **Chemical** | **Carbonation** | The slow dissolution of limestone due to rainfall (weak carbonic acid, pH 5.6) producing calcium bicarbonate in solution. | Limestone and other carbonate rocks.| | **Hydrolysis** | The breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved CO2. | Igneous and metamorphic rocks containing feldspar and other silicate minerals. | | **Oxidation** | The addition of oxygen to minerals, especially iron compounds, which produces iron oxides and increases volume, contributing to mechanical breakdown. | Sandstones, siltstones and shales often contain iron compounds that can be oxidised. | | **Biological** | **Plant roots** | Trees and plants roots growing in cracks and fissures forcing rocks apart. | An important process on vegetated cliff tops that can contribute to rockfalls. Sedimentary rocks, especially carbonate rocks (limestone) located in the inter-tidal zone. | | | **Rock boring** | Many species of clams and molluscs bore into rock and may also secrete chemicals that dissolve rocks. | ## Types of Mass Movement - **a Rockfall** - fragments of rock break away from the cliff face, often due to freeze-thaw weathering - **b Landslide** - blocks of rock slide downhill - **c Mudflow** - saturated soil and weak rock flows down a slope - **d Rotational slip** - slump of saturated soil and weak rock along a curved surface. ## Landforms of Erosion - **Stack** - eroded to leave stump - **Wave-cut platform** - **Caves made larger until an arch is formed** - **Arch collapses to leave a stack** - **Waves erode joints and cracks to form caves** - **Arch, Cave that the "back" has been eroded through** - **Small crack exploited by HA (hydraulic action)** - **PHA makes the crack bigger and creates a cove** - **Wave out under the arch, the arch collapses leaving a stack** **Traction** - Sediment rolls along, pushed by waves and currents - storm. **Saltation** - Sediment bounces along, either due to the force of water or a dry, windy day. - The sound of rolling pebbles and shingles can often be heard clearly at the beach - On a dry, windy day, a layer of saltating sand is often seen 2-10cm above the beach. | **Type** | **Process** | **Explanation** | |---|---|---| | **Suspension** | Sediment is carried in the water column | On soft-rock coasts such as Holderness, the sea is often muddy brown in colour due to suspended sediment | Silt and clay particles. | | **Solution** | Dissolved material is carried in the water as a solution | This type of sediment transport is of limited importance on coasts | Chemical compounds in solution | | **Longshore drift** | This moves material along the beach in the direction of the prevailing wind. | | **Sediment backwash** | Sediment is moved up the beach. | ## Sediment Cells: - Stretches of coastline where the movement of sediment is continued. **Sources:** - Places where sediment is generated, cliffs eroding - Sand dunes, also river systems - **Transfer Zones:** places where sediment is moving down the shore through longshore drift. - **Sinks:** locations where the dominant process is deposition, including spits and offshore bars.