Tides and currents

Question 1

What are tides?

Answer 1

Changes in water levels of seasons and oceans. Caused by the gravitational pull of the sun and moon.

Question 2

What is tidal range?

Answer 2

The difference between high tide and low tide.

Question 3

What is spring tide?

Answer 3

When the sun, earth and moon are linear - in a straight line. During this time the ocean has the highest tidal range = highest high tide and lowest low tide.

Question 4

What is neap tide?

Answer 4

When the moon is 90 degrees either side of the earth from its spring tide position. Not in line w/ the sun.
Neap tide has the lowest tidal range = lowest high tide and highest low tide.
There is a higher rate of erosion concentrated at a certain point.

Question 5

What are the 3 different tidal ranges?

Answer 5

Macrotidal - over 2m
Microtidal - less than 2m
Mesotidal - 2-4m

Question 6

What is an example of a microtidal area?

Answer 6

The Mediterranean Sea has low tidal ranges.

Question 7

What is an example of a macrotidal area?

Answer 7

The British Isles has high tidal ranges.

Question 8

How are currents different from tides?

Answer 8

They transfer mechanisms transporting sediment within the coastal system and beyond it. They are a seasonal or permanent movement of water on the sea/ocean. Waves are created by and driven by the fetch and the wind.

Question 9

What is the Coriolis effect?

Answer 9

Causes a deflection of global wind patterns due to the spinning and curvature of the earth.

Question 10

What is a gyre?

Answer 10

Any large system of circulating ocean currents, particularly those involved w/ large wind movements. Caused by the Coriolis force.

Question 11

What is the global conveyor belt?

Answer 11

A constantly moving system of deep ocean circulation driven by temp. and salinity.

Question 12

How are winds deflected in the northern and southern hemispheres?

Answer 12

Deflected as the anti-clockwise rotation of the earth deflects winds to the right in the northern h. and left in the southern h.

Question 13

What is upwelling?

Answer 13

Movement of cold water from deep in the ocean towards the surface. More cold dense water replaces surface water. Creates rich and cold ocean currents.

Question 14

Why does upwelling occur?

Answer 14

Warmer surface water moves offshore due to surface winds. Deeper, colder and nutrients filled water rises to the surface to replace water that was pushed away.

Question 15

What is downwelling?

Answer 15

The opposite process of upwelling. When surface wind causes water to build up along a coastline and the surface water sinks towards the bottom.

Question 16

What happens as a result of upwelling?

Answer 16

The waters that rise are colder and rich in nutrients so they ‘fertilise’ surface waters. As a result these waters often have high biological productivity and upwelling areas typically are good fishing grounds.

Question 17

What are rip currents?

Answer 17

A strong flow of water running from a beach back to the open ocean.
Water flows out through a breaker zone and strong currents move away from the shore. Seawater is piled up along the coastline due to plunging waves. May initially run parallel to coast.

Question 18

How do rip currents form?

Answer 18

Formed due to a beaches topography. Occur in areas w/ rocky or sand/silt beach topography.

Question 19

Describe the formation of a rip current.

Answer 19

Can form in gaps between sandbars, piers or parts of a reef. These underwater obstacles block waves from washing directly back to the sea. Water from these ‘feeder’ waves runs along the shore until it finds an opening around obstacles. Now a rip current, this water rushes to the opening. Flows quicker than water on either side. Loses pressure and stops flowing once past obstacle.
Dangerous to swimmers.

Question 20

What are longshore currents?

Answer 20

When wave moves towards coast and diff. segments of wave encounter beach before others slowing it down in certain places. Results in wave approaching at an angle. Transports sediment parallel to the shore.