The tide is the periodic rise and fall in the level of the sea, caused by gravitational pull of the sun and the moon (moon has greatest influence though as it is closer to Earth). Gravitational pull of the moon pulls the Earth towards it, creating a high tide on the closest side, and a compensatory bulge (another high tide) on the other side. Halfway between the two high tides on wither side of the Earth are the points at which the tide is lowest.
In general, the high tides follow the moon as it orbits Earth. Twice each lunar month, the Earth, moon and sun are completely in line with each other, so the tide raising force is at its strongest. This produces the spring tide, where it has the highest monthly tidal range
Twice in a lunar month, the sun and moon are perpendicular to each other in relation to the Earth. At this point, it produces the lowest monthly tidal range, called neap tides. It tends to be that there are 4 high tides and 4 low tides at this point.
Other factors affecting tides:
- Morphology of seabed
- Proximity of land masses
- Impact of spinning force on Earth – Coriolis force
- Tidal range – this is the height difference between sea water at high tide and low tide – tidal range determines upper and lower limits of erosion and deposition, and amount of time that the littoral zone is exposed – essentially, landforms develop within the tidal range
- Low tidal ranges operate in the Mediterranean – restricts wave action to narrow width in coastal zone
- High tidal ranges operate in parts of British Isles – wide zone of attack – forms wave-cut platforms
- When range is over 4m, it is called macrotidal
- When range is 2-4m, it is called mesotidal
- When range is under 2m, it is called microtidal