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Weathering Processes & Mass Movement
The Coastal Zone
The coastline is shaped by different processes
These processes are at direct result of MARINE PROCESSES: wave action, erosion, transportation and deposition of materials.
They are aided by weathering of rocks exposed at coast and mass movement
4 Types of Mass movement
Rock fall - fragments of rock break away from cliff, often due to freeze-thaw weathering
Landslide - blocks of rock slide downhill
Mudflow - saturated soil & weak rock flow downhill
Rotational slip - slump of saturated soil & weak rock along a curved surface
Constructive & Destructive waves
Constructive: swash stronger than backwash (carry large amounts sediment > construct the beach), arrive at <10 a minute, smaller in height, formed distant storms
Destructive: backwash stronger than swash (removal sediment > destroy the beach), arrive at 10< a minute, larger in height, formed local storms.
5 Processes of Erosion
Hydraulic action - sheer power of waves as they smash onto cliff, trapped air blast into holes & cracks, eventually causing rock break apart. Explosive force of trapped air called cavitation. Corrasion - fragments of rock picked up & hurled by the sea at cliff. Rocks act like erosive tools by scraping/gouging rock. Abrasion - 'sandpapering effect' pebbles grinding over rocky platform often causing it to become smooth. Solution - some rocks dissolved by seawater, particularly limestone & half which form cliffs. Attrition - where rock fragments carried by sea knock against each other, causing them to get smaller & rounder
4 Processes of Transportation
Traction - large pebbles rolled along sea bed
Saltation - 'hopping' of particles too heavy to be suspended
Suspension - particles carried within water
Solution - dissolved chemicals derived from limestone/chalk
Longshore Drift & Deposition
1. Swash picks up sediment & travel up beach at an angle
2. Due to gravity, backwash carries material down perpendicular to coast.
e.g prevailing winds in Britiain is from SW to material moved from W to E along south coast
Deposition - occurs in areas where flow water slows down and sediment has to be deposited. Common in bays where energy of waves reduced on entering bay. Explains presence of beach in bays and explains the lack of beaches at headlands where wave energy much greater
Headlands & Bays
Bays - broad inlet of the sea where the land curves inwards. Form when less resistant rock eroded first. There is deposition in bays, forming beaches.
Headlands - a point of usually high land jutting out of the sea. Form when more resistant rock left sticking out but then erosion begins to take place at headland.
Wave-Cut Platforms & 4 Cliff Features
Due to processes of erosions, wave-cut notch made at base of cliff & eventually the weight of cliff above too great so cliff collapses. This is cliff retreat. Area under wave-cut notch is wave-cut platform.
Cliff features:
Caves - (hydraulic action & corrasion) formed in weaknesses. Arches - form when a cave continually widened. Stacks - isolated portion of cliff, arch was too heavy so it eventually collapsed. Stumps - stack undercut & collapses to leave a stump, covered up at high tide.
Beaches, Spits & Bars
Beaches - often formed in bays; energy of waves reduced as they slow down.
Spits - formed longshore drift; sea relatively shallow & sheltered; prevailing winds; salt marsh (wildlife habitat) beings to grow behind spit; occasional strong winds from NE turn end of spit.
Bars - a spit that has grown across a bay.
Reasons for Rising Sea Level
- Glaciers & ice sheets are melting.
- Global temps increase - sea water absorbs more heat & expands.
- Affected by rate of global warming.
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