When is tidal range at its maximum

The world's widest tidal range occurs in the Bay of Fundy, in E Canada, where the sea level changes by 40 ft 12 m during the day, while the Mediterranean, Baltic, and Caribbean Seas are relatively tideless. As the tides change, currents must flow to redistribute the ocean's water. In the open ocean, the tidal currents are rotary, shifting through all directions of the compass in a period matching that of the local tide.

When tidal currents flow into the mouth of a river, they speed up. In extreme cases, the tidal rise advances up the river as a solid wall of water often several feet high, a rare phenomenon called a tidal bore. During times of high tide accompanied by high wind and low pressure, as during a hurricane , a tidal surge can occur, causing coastal erosion, flooding, and damage to coastal cities.

When both the Sun and Moon are aligned, the effect of each is added together, producing higher than normal tides called spring tides. Spring tides are tides with the greatest tidal range. They occur exactly halfway between the spring tides, when the Moon is at first or last quarter.

The material that follows on tides was cut from Ocean Movements section under Coastal Processes. Tides are the daily rise and fall of sea level at any given place. The Moon has a greater effect because, although it is much smaller than the Sun, it is much closer. High tide left and low tide right at Bay of Fundy on the Gulf of Maine. The Bay of Fundy has the greatest tidal ranges on Earth at To understand the tides it is easiest to start with the effect of the Moon on Earth.

As the Moon revolves around our planet, its gravity pulls Earth toward it. The lithosphere is unable to move much but the water is pulled by the gravity and a bulge is created. This bulge is the high tide beneath the Moon. This creates a second high tide bulge on the opposite side of Earth from the Moon. Since so much water is pulled into the two high tides, low tides form between the two high tides Figure below. As the Earth rotates beneath the Moon, a single spot will experience two high tides and two low tides every day.

The tidal range is the difference between the ocean level at high tide and the ocean at low tide Figure below. The tidal range in a location depends on a number of factors, including the slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope.

So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive so when the gravitational pull of both bodies is in the same direction the high tides add and the low tides add Figure below. Highs are higher and lows are lower than at other times through the month. This movement is called a tidal current. When the tide is rising, water flows from the ocean into the bay creating a flood current. When the tide falls, water flows from the bay back into the ocean creating an ebb current.

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