The ocean’s surface continuously rises and falls in a predictable rhythm, a phenomenon known as tides. Understanding these movements is fundamental for coastal environments and maritime activities. This natural cycle shapes coastlines, influences marine life, and impacts human endeavors from shipping to recreation.
Defining High Tide
High tide marks the point when the ocean’s water level reaches its maximum height along a coastline. This contrasts with low tide, which occurs when the water level drops to its minimum. Most coastlines experience two high tides and two low tides each day, with a full cycle taking over 12 hours. The difference in height between the high tide and the low tide is referred to as the tidal range.
The Moon’s Gravitational Influence
The primary force driving Earth’s tides is the gravitational pull of the Moon. The Moon’s gravity exerts a differential force across Earth, meaning its pull is strongest on the side of Earth closest to it and weakest on the farthest side. This differential pull causes the oceans to bulge outwards on both the side of Earth facing the Moon and the side directly opposite it. These bulges represent the high tides.
As Earth rotates on its axis, different locations pass through these two tidal bulges. When a coastal area moves into a bulge, it experiences a high tide. Conversely, as it moves out of a bulge where water is drawn away, it experiences a low tide. While the Moon’s gravity affects the entire Earth, water, being fluid, responds more visibly by shifting and creating these tidal bulges.
Solar Impact on Tidal Strength
While the Moon is the main driver of tides, the Sun’s gravitational pull also influences their strength. The Sun’s tidal force is approximately half that of the Moon, primarily because the Sun is much farther away from Earth despite its larger mass. The alignment of the Sun, Moon, and Earth determines whether their gravitational forces combine or counteract each other, leading to variations in tidal range.
When the Sun, Moon, and Earth align in a straight line, which occurs during new and full moon phases, their gravitational forces combine. This alignment results in “spring tides,” characterized by higher-than-average high tides and lower-than-average low tides. Conversely, when the Sun and Moon are at right angles to each other relative to Earth, their gravitational pulls partially cancel each other out. This configuration produces “neap tides,” which have a smaller tidal range, meaning high tides are lower and low tides are higher than average.