Beaches and Beach Processes
Beach Processes
What are some common features of beaches?
Do we see all these features at every beach?
Why are there different features at different beaches?
Tides
What is a tide?
Daily changes in the elevation of the ocean
What causes tides to occur
Created by gravitational pull on the earth by the Moon and the Sun
Causes Ocean water to “deform” into bulges
Earth rotates through these bulges
What is a spring tide?
Highest high tides and lowest low tides
What moon phase do these occur during?
What is a neap tide
High and low tides are very similar to each other
What moon phase do these occur during?
How many tidal changes are there each day?
Tide frequency patterns
Diurnal : One high and one low tide each day
Semi-Diurnal 2 highs and 2 lows each day
Mixed: 2 highs and 2 lows each day
Where each type occurs on the earth
How do tides affect the coastline?
Flood currents
Slack water
Ebb currents
All the above transport sediment
Tidal Flats
What are other processes on the coast that move sediment?
Rivers
Estuaries
Waves
Waves
What causes waves?
Solar radiation--> warms atmosphere-->creates wind--> friction of wind creates waves
Waves transfer energy
Wave motion
Deep water ocean waves have oscillatory motion
What happens when waves approach the shoreline?
Translational motion
Breaker Zone
Swash and Backwash
What controls the size, period and speed of waves?
Wind speed
Wind duration
Constant wind direction
Fetch (distance the wind blows)
Beach Features
What effect do Tides and waves have on beaches?
How tides and waves affect the beach are determined primarily by the morphology of the
continental shelf
Continental shelves and slopes
Continental shelf is the part of the continent that is under water.
Continental slope is the very edge of the continent
Whether waves will erode or deposit depend on…
Where the waves break
Big shelf vs Small shelf
What type of continental shelf does Oregon have
Google earth
Size of the waves
Winter or summer
What is the beach made of?
Sand or Rock
Different types of sands at different beaches
What is available to make the sand
Olivine
Basalt
Shells
Quartz
Etc….
How do waves transport sediment or erode beaches
Wave refraction
Waves approach shoreline at angle
Wave bends as it approaches shoreline
Causes longshore current
longshore drift
Erosional Features
Wave cut benches or platforms
Headlands
Sea Caves and Arches
Sea Stacks
Rocky Coast line
Stopping Erosion?
Why would we want to?
Methods used for slowing erosion
Breakwaters
Structure that is parallel to shoreline
Groins & Jetties
Right angle to beach
Seawalls
Parallel to shoreline…right on beach
Beach nourishment
Deposition
Why does deposition occur on beaches?
When is deposition dominate on the Oregon coast
Beaches created by deposition of local material
sand, coral, rocks
Longshore current creates many features
spits, baymouth bars, tombolos
Special features
Barrier islands
Emergent vs Submergent coastlines
Emergent
Uplift of the coast line is occurring
What features would you see?
Submergent is subsidence
What features might you see
Coral reefs and Atolls
What is a coral reef?
Fringing Reef
Barrier Reef
Atoll
