(TE) Tides Flashcards

1
Q

What is the “tidal bulge”

A

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

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2
Q

How often does a tidal bulge pass over one location?

A

12.5 hours

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3
Q

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

A

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

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4
Q

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

A

Diurnal bulge inequality

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5
Q

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

A

Syzygy

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6
Q

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

A

Tidal effects are cancelled as they are at 90 degrees

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7
Q

When do spring tides occur?

A

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

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8
Q

When do neap tides occur?

A

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

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9
Q

What is the relative size of neap tides?

A

Smallest tides

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10
Q

What is the relative size of spring tides?

A

Largest tides

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11
Q

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

A

Annual - Equinoxes closest to sun

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12
Q

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

A

Resonance of waves

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13
Q

Give an example where resonance causes large waves

A

Bay of Fundy - Canada - 15m tides

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14
Q

What is an amphidromic cell?

A

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

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15
Q

What is an amphidromic point?

A

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

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16
Q

What is the height range for microtidal?

A

<2m

17
Q

What is the height range for mesotidal?

A

2 - 4m

18
Q

What is the height range for macrotidal?

A

> 4m

19
Q

What height range has the weakest tides?

A

Microtidal

20
Q

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

A

Larger tides can carry more sediment due to more energy

21
Q

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

A

Pressure differences

22
Q

What are rotary tides?

A

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

23
Q

What does bimodal mean?

A

Two main directions of flow

24
Q

What does bipolar mean?

A

Two opposite directions of flow

25
Q

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

A

Many years - not a diurnal occurance

26
Q

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

A

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

27
Q

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

A

Various proportions of mud/sand

28
Q

Give an example of a reactivation surface

A

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

29
Q

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

A

Tidal bundles

30
Q

What do tidal bundles look like in a perfect situation?

A

Cycles of 7 or 14 multiples

31
Q

Why are perfect tidal bundles so rare?

A

Often no sedimentation or bedforms during weaker parts of cycle