GEOG 100--Lecture 17--Coastal Geomorphology
22 likes8,877 views
This document summarizes key concepts in coastal geomorphology. It discusses ocean water properties like salinity, temperature, and density which vary based on location. It also describes ocean currents and how they transport heat. Tides are explained as being caused by gravitational pull from the moon and sun. Extreme tides can form landforms. Waves are generated by wind and their characteristics depend on fetch and strength. Waves transform and transport sediment along shorelines via processes like refraction and longshore drift. Erosional and depositional coastal environments are shaped by these processes. Finally, human impacts like stabilization structures are discussed.
GEOG 100--Lecture 17--Coastal Geomorphology
- 1. Coastal Geomorphology: The Oceans, Coastal Processes, and Landforms Chapter 12
- 2. Ocean Water: Salinity, Temperature, and Density • Salinity – Dissolved mineral salts (sodium chloride, magnesium, sulfur, calcium, potassium, etc.) – Differences in salinity are related to evaporation rates and fresh water inflow • Avg. max. salinity found in subtropics (high evap., low precip.) • Avg. min. salinity found in tropical regions (fresh water from high precipitation, low evaporation due to high atmospheric saturation)
- 3. Ocean Water • Temperature –Decreasing temperatures with increasing latitude •Polar water = cold, equatorial water = warm –Decreasing temperatures with increasing depth •Deeper waters are colder (sunlight can’t reach, there is little or no mixing) –Western sides of oceans are warmer due to ocean circulation patterns (see next slide)
- 4. Warm and Cold Ocean Currents
- 5. Ocean Water • Density – Related to temperature • low temp. = high density – Molecules are less active, so cold water contracts – Related to salinity • high salinity = high density – More solids in the water (salts) increases overall density – Related to depth • deep water = high density – Pressure of water above compresses deep water, increasing density
- 6. The Movements of The Oceans • Tides • Currents • Wave motion
- 7. Tides • A “bulge” in the world’s oceans, caused by the gravitational pull of the moon and sun Fg = G m1 m2 d2
- 8. Tides • Tidal range—the difference between high and low tide • Affected by the shape of the coastline and seafloor • Spring tides—highest tides, strong and quick – Occur when sun, moon, and Earth line up (the sea “springs” up and back) • Neap tides—lowest tides – Sun and moon at right angles with respect to Earth – Neap = A low incline of bend (when graphed)
- 10. Extreme High Tides • The Bay of Fundy • A 50’ (15m) tidal fluctuation is common (x2) •A tidal bore (several in. to several ft. high) rushes miles up the Petitcodiac River in New Bruswick
- 11. Landforms shaped by extreme tides
- 12. Extreme tides: Mont Saint Michel, France Low tide High tide 12
- 15. Waves and Wave Dynamics
- 16. Waves and Wave Dynamics • Period—The time it takes two successive waves (from crest to crest, or from trough to trough) to pass a given point • Fetch—The distance over which the wind blows, creating waves
- 17. Waves and Wave Dynamics • Factors affecting open ocean waves: –Fetch •The greater the distance over which the wind blows, the larger the waves –Wind strength •The stronger the wind, the larger the waves –Wind duration •The longer the wind blows, the more waves will be created
- 18. Waves and Wave Dynamics Wave base
- 19. Waves of Oscillation (Transition) and Waves of Translation • Water molecules on the open ocean move in a circular motion – The motion passes through the water, but the water doesn’t move forward (to oscillate is to move up and down) – What moves the water forward is wind blowing over the surface and the movement of currents • Water molecules that reach the shore have their circular motion interrupted – Their energy is translated into the shore face (it passes from the water to the land, where it does work to move material—like sand—around)
- 20. Waves and Wave Dynamics Waves of translation Waves of oscillation
- 21. Wave Break
- 22. Wave Refraction and Longshore Current • As waves reach the shore and “feel” the bottom, they slow and break • The direction of wave break follows the underwater topography • This causes the wave to “bend” and become more parallel to the shoreline – This bending is called wave refraction • As it breaks from one side to the other, it creates a current – This current, called the longshore current picks up and moves sediment (sand) down the shore
- 23. Wave Refraction, Longshore Current and Beach Drift
- 24. Erosional Environments • If there is not enough sediment replacing what’s being lost through wave erosion/longshore current, erosion will occur, creating a rocky coastline – Dammed or channelized streams • sediment can’t get to the beach • Erosive environments create distinctive landforms – rocky headlands and pocket beaches, sea arches and sea stacks, wave-cut cliffs, wave-cut platforms, wave- built terraces, etc.
- 25. Wave Energy is Concentrated at Headlands and Dissipated in Bays
- 26. Wave Motion and Wave Refraction
- 27. Wave Motion and Wave Refraction
- 28. Laguna Beach, CA Headlands
- 29. Headland Erosion and the Formation of Sea Arches
- 30. Stacks and Cliffs Victoria, Australia
- 31. The Holderness Coast is one of Europe's fastest eroding coastlines. The average annual rate of erosion is around 2 metres per year. The main reason for this is because the bedrock is made up of till. This material was deposited by glaciers over 18,000 years ago.
- 32. Depositional Environments: The Structure of a Beach
- 35. Barrier Island Coast Padre Island, Texas 35
- 36. Lagoons, Marshlands, and the Formation of New Coastlines
- 37. Coastal Stabilization and Human Impact “Any serious researcher would be hard- pressed to find a marina, a sea wall, or any other human structure along the shoreline that does not pose some long-term deleterious effects to both the natural and cultural environments it attempts to protect.” --Physical Geography: Earth’s Interconnected Systems Angela Orr, 2007
- 38. Coastal Stabilization and Human Impact • Damming and channelizing streams –Causes a loss of sediment where streams empty into the sea. Without sediment, the beach will erode away. • Groynes (groins) • Seawalls • Breakwaters and jetties 38
- 40. Groynes (groins) 40
- 41. • Can you tell which way the longshore current is moving material? • Once you put up one groyne, you need to keep building them all along the shore to keep erosion from destroying property downshore from your first structure. Note the severe erosion at the top of the photo where the groynes stop. 41
- 42. Breakwater
- 43. Breakwater • These breakwaters are creating tombolos in the wave shadow behind them. 43
- 44. The Example of Marina del Rey, CA