Rob 1 Flashcards
Where does the coastal zone start?
Where waves start hitting the ocean floor and consequently move sand - wave base
How does where the coastal zone starts vary?
Depending on wave size. The wave base will be further out from the beach if wave size is larger
What are waves?
circular motion of water particles which moves sediments
What happens to wave size as you move further from the waters surface?
The waves get smaller and smaller
Coasts are dynamic! How do we study them?
On a temporal (sec/min/hour/day/yr) and a spatial scale (length scale)
When studying coasts on a temporal and spatial scale what are the 4 categories you end up with?
- Insantaneous
- Event -Engineering - Geological
What did the first people who studied coastal science do?
They made things up because they didn’t have instruments to measure variables
Darwin
Travelled through south pacific on his journey and saw a lot of coral reefs. Came up with theory about how coral reef forms. Came up with 3 ideas of the reefs and said they were related because the island sink
Darwins 3 types of coral reef
- Fringing: coral reefs stuck to shore lines of islands
- Barrier: separated from island by lagoon
- Atoll: circular ring of reef
Why will coral be left behind if a island sinks
Coral grows to the surface of ocean so if a island sinks the coral will remain. Islands sink because they are sitting on tectonic plates
What is darwin’s theory of coral reef evolution a example of
Just coming up with a observation and then it being right
WW2
Any war - exhilaration of technology. ww2 d-day invasion alot of time they hit a sand bar of shore. Hit deep trough between sand bar and tough = drowning. Due to a lack of understanding about coastal sandbars.
Following WW2 what happened and why?
Military had a perspective that they needed to know more about the coastlines and waves. Start measurement programme that all of the american coastline was surveyed. Mapped out the coastline = empirical approach
1960’s
Took 2 approaches
- Sedimentary (geological) approach (1960+)
- Geophysical Principles approach
Sedimentary / geological approach
From the 1960’s- look at the size and angle of sand particles. Use cores- sediments and statigraphy
Geophysical principles approach
1960+. apply physical principles of matter and motion - look at water motion over sand and how sand is suspended
1970’s
Morphodynamic Approach
Stratigraphy
Branch of geology concerned with order and relative position of strata
1970/morphodynamic approach : what does it say
All these enviro controls on a coastal system. The system is like a engine and upi have processes like waves and currents and tides which are moving and driving sand. Movement will change shape of beach and different shaped beach will affect the processes. A interconnected system
What does the interconnected morphodynaic approach mean for humans?
If humans alter something it will change everything else. Understand 3 boxes
Processes drive…
..the sediment transport.. which drives the beach morphology.. drives the processes (interlinked)
Coastal controls
- Geology
- Sea level
- Wave climate
- Tide range
- Daily processes
Geology as a coastal control
Hard rock - coastlines don’t change often!
Soft rock - coastlines change alot!
The different scales as geology as a coastal control
- Global : plate tectonics
- Regional: Continental shelve and sediment type
CC - Geology : plate tectonics
GLOBAL scale! Boundaries of tectonic plates tend to be on coastlines, e.g. west coast of NA. NZ has plate boundary through it. Get 2 types of coasts based on where the coast is relative to plate boundaries
CC - Geology - 2 types of coast:
- Collision Coast
- Trailing edge coast
- under different pressures = get different looking coastlines
- end up with different appearances
Collision coast
2 plates smashing in to each and the light plate will go under the heavier one. Friction. Cause mountain building and volcano’s
Appearance of a collision coast
Mountainous. Beaches but generally not alot of sandy beaches
E.g. NZ - Rocky -Steep -Mountainous
Appearance of trailing edge coast
Flat
Alot of sand
E.g. florida
Alot of dunes
Continental shelve she
Every coastline has one. Where the coast just drops of into the beach deep ocean. Different places in world have different extent of coastal shelve. Sydney has a very narrow continental shelve
NSW gets good surf bc
V narrow continental shelve and v steep! Waves coming in - nothing slows them down!
Why are Continental shelves important?
- Surf
- Tsunami
Tsunami and continental shelve
Suited to a wide continental shelve - make them get bigger ! = NSW via its geology is totally protected from a large impact of a tsunami
Final geological control is..
The sediment type .. on a regional scale!
What are the different types of sediment
Gravel
Sand
Mud
Bioclastics
Tropics beaches
Wet and hot! alot of mud! Not great beaches
Gravel
Mostly in coastal area’s which have been glaciated. Not many in Aus because old country but NZ is a relatively new country so they have lots of gravel beaches
Sand
Mostly in the lower and middle latitudes
Mud beaches
most common in humid, temperate or tropical hot climatic zones
Bioclastics
Bits of shells and coral
What is the second control about what the coastline looks like?
Sea level!
Quarternary and sea level
Period which goes back the last 2 mil years - sea level has been going up and down like a yoyo
Where the sea level is today
Unusual in terms of where it has been in the past! Its only been at its present location a few times in the Quaternary period
Why does sea level change
- Movement of plates, e.g. more volcanic activity changing temperature (ice).
- Astronomical : earth rotates round the sun but it goes as a elipse : eccentricity. And it tilts and wobbles. Sometime eccentricity, tilt and wobble line up and the earth is closer to the sun! Earth gets warmer and the ice melts! Roughly happens 40,000-60,000 years apart - regardless of CC we will eventually get a ice age
Eustasy
Means a global change
Glacio-Eustasy
When earth gets cold and have ice at poles sea levels worldwide will fall by about 100 metres
Isostasy
Local change in sea level. Ice is really heavy!
Isostatic rebound
After ice pushing down a continent when the ice melts and pushes the coast back up! It called isostatic rebound
Isostatic rebound makes the sea level look ..
.like its falling
What are the 2 main effects of ice on the coastline
Ice affects the volume of water in the ocean
-The ice affects the rebound of shorelines
Hydro-isostasy
Water is heavy. The weight of water can push down the continental shelve a little bit - looks like sea level is rising
Sediment Isostasy
Sand is heavy. Push down! New Orleans
What happens if you heat up water?
It expands
Tectonic plate
Earth quake pushes up a big section of land! Makes the sea level look like it has gone up or down
Ocean temperature
If the ocean temp increases by 1 degree it will cause sea level to rise by 2m
Scotland
been going through a isostatic rebound since the last ice age
The story of bondi beach
Go back 18,000 yr ago! Had a ice age- sea level is 120 metres lower ! Sydney harbour was dry! Could walk to tasmania.
So 18,000 years ago bondi beach would have been a woodland. Had big rivers coming down and carrying sand from outback which was dumped on beaches! When sea level rised the sand got pushed back into the old river valleys
Why geology is important
It gives the shape of the coastline, e.g. old ancient river valleys - have little pockets for the sand to go into and create beaches
Bondi sand
Bondi sand has came from the coastline
Sea level rise between 18,000 years ago and 6,000 years ago was…
..way faster than anything we predict today due to anthropogenic climate change
Sea level change.. in the past
1800’s didnt have instruements to tell us what was going on so guessed! Then we developed tide gages in last 100 years - predictions got good -
What does the tide gages tell us about climate change in the last 100 years?
That sea level has gone up by about 100cm
We know sea level is rising but..
..even the best scientists globally don’t know by how much. Some people think its a couple of cm..others think metres! uncertainty!
What does the uncertainity mean?
No politician will invest in sea level rise- why it is important that we get better at predicting it
What is the 3rd coastal control?
Wave climate, e.g. average wave height, direction and often but may have storms super imposed on this. There are different wave climates around the world
What wave climate categories have been produced
- Storm waves
- Protected sea’s
- East coast swell
- Cyclone influence
- Monsoon/trade wind influence
- West coast swell
lower latitudes
- windy
- roaring 40’s
wind =
waves
Big difference between north and south
The north has more land - northern hemisphere - dont have as much waves
Wave climate depending on where you are..
Different areas will have different wave climates!
What is the fourth coastal control?
Tides