tides& tidal surges Flashcards
what are tides?
tides are the periodic rise and fall in the level of the sea.
how are tides caused?
They are caused by the gravitational pull of the sun and moon, although the moon has much the greater influence because its nearer.
What does the moon do?
The moon pulls water towards it, creating a high tide and there is a compensatory bulge on the opposite side of the earth. In areas of the world between the two bulges, the tide is at its lowest.
how is a spring tide formed?
- Moon orbits the earth, the high tides follow it.
- twice in a lunar month, when moon, sun& earth are in a straight line.
- the tide- raising force is strongest
- Which produces highest monthly tidal range or spring tide.
How are neap tides formed?
- Twice a month the sun and moon are positioned at 90 degrees to each other in relation to the earth.
- This alignment gives the lowest monthly tidal range, or neap tides.
The high and low tides are between 10 and 30 per cent lower than average.
What is a tidal range?
can be a significant factor in the development of a coastline
Tidal range is the difference in height of sea water at high and low tide.
Tidal ranges determine what?
The upper and lower limits of erosion and deposition and the amount of time each day that the littoral zone is exposed and open to sub- aerial weathering.
Tidal ranges are low where?
Along the coasts of the Mediterranean sea.
This restricts wave action to narrow width in the costal zone.
where are tidal ranges high?
British Isles.
This gives a wide zone of wave attack.- resulting in the formation of wave-cut platforms in many places.
What are tidal or storm surges?
Are occasions when meteorological conditions give rise to strong winds which can produce much higher water levels than those at high tide.
example of storm surge?
North sea and east coast of Britain.
depressions over the north sea produce low pressure conditions that have the effect of raising sea levels.
sea level can rise by one centimetre for every one millibar drop in pressure.
strong winds do what during a storm surge?
strong winds drive waves ahead of the storm, pushing sea water towards the coastline.
results in piling- up water against the coast.
what does the shape of the north sea mean?
water is often increasingly concentrated into a space that is decreasing in size. High tides, especially those of a spring tide, intensify this effect.
when did the north sea tidal surge occur?
1953
