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coastal weathering, mechanical(physical weathering): mechanical weathering…
coastal weathering
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oxidation- the reaction of rock minerals with oxygen, for example iron, to from a rusty red powder leaving rocks more vulnerable to weathering
it can range from being extremely slow-less than 1 cm a year(e.g. soil creep)- to horrifyingly fast(e.g. rockfalls and landslides). mass movement at the coast is common-the sheer weight of rainwater, combined with weak geology, is the major cause of cliff collapse.
mechanical(physical weathering): mechanical weathering involves the break-up of rocks without any chemical changes taking place. there are several types of mechanical weathering processes that are active at the coast
frost shattering(also known as freeze-thaw occurs when water enters a crack or joint in the rock when it rains and then freezes in cold weather. when water freezes, it expands in volume by about 10%. this expansion exerts pressure on the rock, which forces the crack to widen. with repeated freezing and thawing, fragments of rocks break away and collect at the base of the cliff as scree. these angular rock fragments are then used by the sea as tools in marine erosion
salt crystallization when salt water evaporates, it leaves salt crystals behind, these can grow over time and exert stresses in the rock, just as ice does, causing it to break up
wetting and drying. frequent cycles of wetting and drying are common on the coast. rocks rich in clay expand when they get wet and contract as they are dry. this can cause them to crack and break up
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mass movement:: the downhill movement of material under the influence of gravity is known as mass movement
:types of mass movement
soil creep soil creep is an extremely sloe from of movement of individual soil particles downhill. the precise mechanism pf movement often involves particles rising towards the ground surface due to wetting or freezing and then returning vertically to the surface in response to gravity as the soil dries out or thaws. the zigzag movement is similar to that of longshore drift. soil creep cannot be seen operation but its action can be implied by the formation of shallow tetraacetates and the build-up of soil on the upslope side of walls and the bending of tree trunks
mudflows: involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock such as clay, often after heavy rainfall. water gets trapped within the rock, increasing pore water pressure, which forces rock particles apart and leads to slow failure. pore water pressure is a from of energy within the slope systems and it is an extremely important factor determining slope instability. mudflows are often sudden and fast-flowing so can represent a significant natural hazard
landslide a landslide involves a block of rock moving very rapidly downhill along a planar surface( a side plane), often a bedding plane that is roughly parallels to the ground surface. unlike a mudflow, where the moving material becomes mixed, the moving block of material in a landslide remains largely intact. landslides are frequently triggered by earthquakes or very heavy rainfall, when the slip surface becomes lubricated and friction is reduced. Landslides tend to be very rapid and pose a considerable threat to people and property. in 1993, 60 m of cliff slid onto the beach near Scarborough in North Yorkshire, taking with its part of the Holbeck hall hote l
Rockfallrockfall involves the sudden collapse or breaking away of individual rock fragments at a cliff face. they are most commonly associated with steep or vertical cliffs in heavily jointed and often quite resistant rock. a rockfall is often triggered by mechanical weathering(particularly freeze thaw) or an earthquake. once broken away from the source, rocks fall or bounce down the slope to form scree at the foot of the slope. scree often forms a temporary store within the coastal system, with material gradually being removed and transported elsewhere by the sea. when this occurs the scree forms an input into the sediment cell
landslip or slumpa landslip or slump differs from a landslide in that its slide surface is curved rather than flat. landslips commonly occur in a weak and unconsolidated clays and sands, often when permeable rock overlies impermeable rock, which causes a build-up of pore water pressure. landslips or slump's are characterized by a sharp break of slope and the formation of a scar. multiple landslips can result in a terraced appearance on the cliff edge
runoff is a good illustration of the link between the water cycle and the coastal system. when overland flow occurs down a slope or cliff face, small particles are moved downslope to enter the littoral zone, potentially forming an input into the sediment cell. runoff can be considered a type of flow that transfers both water and sediment from one source (the rock face) to another(a beach/sea)
solifluction: is similar to soil creep but specific to cold periglacial environments. in the summer, the surface layer of soil this out and becomes extremely saturated because it lies on top of impermeable frozen ground(permafrost). known as the active later, this sodden soil with its blanket of vegetation slowly moves downhill by a combination of heave and flow. solifluction characteristically forms features called solifluction lobes
In February 2014, following the wettest winter on record, the Jurassic coast near Lyme Regis in dourest was affected by a number of dramatic landslips, damaging holiday chalets. this exposed stretch of coastline and it constantly being shaped and reshaped by processes of mass movement invigorated by undercutting by the sea
mass movement forms an important group of processes and flows within the coastal system, transferring both energy(in response to gravity) and sediment. the sediment forms an important input to shoreline processes, forming the 'tools' for erosion and providing material to be transported and deposited elsewhere along the coastline. mass movement, along with cliff erosion, provides an important input to sediment cells
chemicals weathering, involves a chemicals reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded
carbonation-rainwater absorbs carbon dioxide from the air to from a weak carbonic acid. this reacts with calcium carbonate in rocks, such as limestone and chalk, to from calcium bicarbonate, which is easily dissolved. the cooler the temperature of the rainwater, the more carbon dioxide is absorbed(so carbonate is more effective in winter
solution- the dissolving of rock minerals, such as haite(rock salt)