(TE) Tides

Question 1

What is the “tidal bulge”

Answer 1

Two bulges of water formed from the graviational pull of the moon

Question 2

How often does a tidal bulge pass over one location?

Answer 2

12.5 hours

Question 3

What is the cause for the difference in time between Earth’s rotation and time for a tidal bulge to pass over?

Answer 3

30 min difference is caused by the slightly slower rotation of the moon

Question 4

What is the name for the phenomenon where one tidal buldge is greater than another?

Answer 4

Diurnal bulge inequality

Question 5

What is the name for when the moon and sun are alligned adding to the height of a tidal bulge?

Answer 5

Syzygy

Question 6

What happens when the sun and moon are in quadratic alignment?

Answer 6

Tidal effects are cancelled as they are at 90 degrees

Question 7

When do spring tides occur?

Answer 7

When there is a full and new moon - twice in a lunar cycle

Question 8

When do neap tides occur?

Answer 8

When the moon is perpendicular to the sun - twice in a lunar cycle

Question 9

What is the relative size of neap tides?

Answer 9

Smallest tides

Question 10

What is the relative size of spring tides?

Answer 10

Largest tides

Question 11

Aside from dirunal and lunar tidal cycles, what is the third cycle?

Answer 11

Annual - Equinoxes closest to sun

Question 12

What is the reason for larger waves in bays and narrow straits?

Answer 12

Resonance of waves

Question 13

Give an example where resonance causes large waves

Answer 13

Bay of Fundy - Canada - 15m tides

Question 14

What is an amphidromic cell?

Answer 14

A cell of water which circulates around a point due to the coriolis effect

Question 15

What is an amphidromic point?

Answer 15

The point which a tidal cell circles around - no change in water level

Question 16

What is the height range for microtidal?

Answer 16

<2m

Question 17

What is the height range for mesotidal?

Answer 17

2 - 4m

Question 18

What is the height range for macrotidal?

Answer 18

> 4m

Question 19

What height range has the weakest tides?

Answer 19

Microtidal

Question 20

What does height range of tides have to do with sediment regieme?

Answer 20

Larger tides can carry more sediment due to more energy

Question 21

What is the main control over the strength of tidal flow?

Answer 21

Pressure differences

Question 22

What are rotary tides?

Answer 22

Rotational waves around amphidromic cells which may not have a period of slack water

Question 23

What does bimodal mean?

Answer 23

Two main directions of flow

Question 24

What does bipolar mean?

Answer 24

Two opposite directions of flow

Question 25

What is the timescale for the formation of herringbone cross-stratification?

Answer 25

Many years - not a diurnal occurance

Question 26

What is the reason for the retention of mud-drapes in tidal cross-strata?

Answer 26

Deposited in an ebb, and it’s cohesive nature keeps it at the bed

Question 27

What does the presence of flaser/lenticular laminations depend upon?

Answer 27

Various proportions of mud/sand

Question 28

Give an example of a reactivation surface

Answer 28

Unidirectional cross-stratification truncated by reverse current, bedding builds up again ontop

Question 29

What is the name for a variation in thickness of foreset laminae caused by tidal cycles?

Answer 29

Tidal bundles

Question 30

What do tidal bundles look like in a perfect situation?

Answer 30

Cycles of 7 or 14 multiples

Question 31

Why are perfect tidal bundles so rare?

Answer 31

Often no sedimentation or bedforms during weaker parts of cycle