Oceans and Coasts Flashcards
What is a continental shelf?
- A continental shelf is a shallow sea produced by continental crust which is submerged under water.
- These cannot be produced at subduction zones however.
What is an abyssal plane?
A large, flat area found at the deepest point of an ocean.
What is a continental shelf?
The transition from continental crust above sea level to that below sea level, producing a very gently sloping continental shelf.
What is a continental slope?
At the end of the continental shelf is a steeper slope known as the continental slope which descends down into the abyssal plane.
How are deep sea fans produced?
Rivers flow in submarine canyons, producing deep sea fans once the speed of flow reduces and the sediment is deposited.
How are tsunamis produced?
Some material on the continental slope is eroded away producing submarine landslides which displace lots of water which can produce tsunamis.
How are turbidity currents produced?
- Turbidity currents are produced from landslides and cause materials to mix with water before gradually settling out.
- This produces layered deposition with coarser materials being deposited first followed by finer materials.
- This process repeated, creating a sequence of deposits.
What is the calcium compensation depth?
- Below this depth, calcium carbonate just dissolved and so deposits such as shells cannot be found.
- The deep ocean deposits are instead dominated by clays.
What are the features of waves?
- They are measured by wavelength.
- The motion of individual particles of water within the wave just move in circles.
- The size of these circles decreases with depth.
- Once the sea bed enters the influence zone, the wave slows down.
What is the action of a wave?
- Waves are slowed down as the water gets shallower.
- Therefore, if the wave has a particular wavelength, the wave must get steeper (eventually forming a breaker) as the time between crests must remain constant.
- This allows the wave to run up the beach (wash) with lots of power, where it is able to move rather large particles.
- When the water comes to a halt, it slowly falls back down into the sea (backwash), where it is only able to move finer particles.
- This produces large deposits of coarsely sized particles at the back of the beach, and finer particles as you move closer to the sea.
How are curved waves produced?
- If a wave approaches the shore at an angle the end which hits the shallow water first slows down (and so has a shorter wavelength), whilst the other end continues at its original speed (longer wavelength).
- This causes the wave to curve (refract) into the beach.
- If there is a headland of hard rock, you get a gentle curve of the beach around it following the refraction of the waves producing it.
What is longshore drift?
- Water approaches the beach at an angle due to the direction of wind.
- It then moves directly backwards into the sea due to gravity.
- This produces a general drift of current which resembles the overall movement of water and particles.
What are the features of tides?
- A high-and-low level means all of the above effects happen in two different places.
- The more gently sloping the beaches, the further apart these two places can be.
- This can lead to two completely different beach profiles.
- A tidal flat is a location where a tidal lagoon is formed between the high and low tide beaches.
Which factors affect tides?
- A tide is a consequence of the gravitational attraction of the sun/moon.
- The water closest to the moon bulges towards it as it experiences the greatest gravitational force.
- The water farthest from the moon bulges away from it as it experiences a weak gravitational force.
- The Earth also bulges but the effects are minuscule.
- The bulge of the water is fixed relative to the position of the moon.
What is a spring/neap tide?
Spring tides:
- Sun and moon are in alignment, so effect are reinforced producing a greater tidal difference.
Neap tides:
- Sun and moon are at 90o to each other, so effects are counteractive producing a smaller tidal difference.