The Coast Section 6 Part II Isostasy weighing
- Slides: 21
The Coast Section 6 Part II
Isostasy �“weighing the same” �Buoyant properties of layers of rocks that float on other layers (due to density and thickness) �Crust ‘floats’ on denser, underlying layer
Continental shelf �Continental shelf – gently sloping region surrounding continents (sea is relatively shallow) �Covered in sediments (erosion of continents) �Part of continent was above sea level during ice age (sea level was lower then) �Water depth over continental shelf depends on 2 factors: � Isostatic changes in land height � Changes in sea level
Principle of Isostasy �Crust is higher where it is thicker and less dense �Lower = thinner and denser Layer Density = g per cm 3 Continental Crust 2. 7 – 3. 0 Sediments on continental shelf Oceanic crust 2. 4 Mantle 3. 3 – 5. 7 3. 0 – 3. 3 Highest density
�Continental crust – mostly made of granite (less dense rock) �Granite: igneous rock made with ~20% quartz �Oceanic crust – basalt (more dense rock) �Basalt: igneous rock less than 20% quartz, mostly volcanic �So, continental plates ride on the denser oceanic plates
Littoral Zone �Land meets sea �Nature of shore factors: �Geology of adjacent land �Exposure to erosion by sea �Area of coast between high water mark and lowest part of submerged shore
Rocky Shore �Rock exposed to sea erosion �Variety sized boulders, stones and pebbles �Granite = resistant to weathering �Sandstone = easily broken down
Rocky Shore �Most exposed type of shore �Most resistant to erosion �Largest boulders left at the top of the shore due to pounding waves �Very steep cliffs to horizontal flat rocks with a wavecut platform
Limiting Factors Rocky Shore �Support wide range of organisms �Stable substrate �Large rocks and stones – firm surface �Algae �Mollusks and cnidarians (and sea anemones) �Rock pools retain water when tide recedes
Rocky Shore �Environmental Factors that influence communities: �Desiccation (extreme drying) � Species near top of shore exposed to air for longer periods �Temperature �Wave action �Light intensity �Aspect �Slope �Nature of substrate
Sandy Shores �Erosion of sandstone �Deposition of sand by the sea �Silica and other minerals �Slope gradually toward sea
Sandy Shores �Unstable �Fine particles are easily moved by winds and tides �Not a suitable substrate �Sea weeds �No shelter for organisms at surface �Under: burrowing organisms �Ghost crabs, bivalve mollusks, annelid worms (ragworms and lugworms) �If sand mixed with muddy deposits, more stable and supportive
Muddy Shores �Least exposed to erosion �silt particles can settle �Very fine mineral sediments �Organic remains �Little slope �Can form mud flats
Estuary �Semi-enclosed body of water �Freshwater meets sea water �Muddy substrate – slow flow of water allows suspended particles to settle
Delta (∆) Get their name from the Greek letter �River carrying suspended sediments reaches large body of water (lake or ocean) �River increase in width = flow rate decreases �Suspended sediments settle �Accumulate into a fan-shaped structure over time �River divides to form distributary channels � 2 examples (next page)
Nile River Delta ∆
Mississippi River Delta ∆
Diameters of Mineral Particles Particle Type Diameter (mm) Silt 0. 002 to 0. 02 Fine Sand 0. 02 to 0. 2 Coarse Sand 0. 2 to 2. 0 Gravel (small stones) > 2. 0
Mangroves (Swamp, Forest) �Trees and shrubs in tropical/subtropical saline coastal habitats �Between 25⁰N and 25 ⁰S �Form woodland or shrub land habitat (coastal/estuarine conditions where sedimentation of silts occur) �Specifically adapted to: �Wide range of salinity �Low oxygen concentrations in sediments
Mangroves �Pneumatophores - specifically adapted root-like structures that obtain oxygen directly from air �Extensive root systems: �Trap particles suspended in water �Reduce water flow � Increases deposition of sediments �Dissipates wave energy � Protects coastal area from erosion �Habitats for: � Algae, oysters, crabs, barnacles and other crustaceans, sponges, fish
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