What Is A Spring Tide?
QUICK ANSWER
A spring tide is the largest tidal range, occurring at new and full moons when the sun and moon align with Earth. The combined gravitational pull produces higher high tides and lower low tides. Spring tides happen about every two weeks and have nothing to do with the season spring.
A spring tide is the largest tidal range of the lunar cycle, occurring twice a month when the sun and moon align with Earth. The name 'spring' refers to the tide 'springing forth' rather than the season. Understanding spring tides explains why some weeks have dramatically larger tide ranges than others and why coastal flooding is more likely on certain days.
When do spring tides happen?
Spring tides occur twice each lunar month: at new moon (when the moon is between Earth and sun) and at full moon (when Earth is between sun and moon). In both cases, the sun and moon are aligned along an axis through Earth, even though on opposite sides. The alignment means their gravitational tidal effects add together rather than partially canceling. Spring tides occur about every 14 days, so coastal areas experience them roughly twice a month.
Why do they have larger ranges?
Spring tides have larger ranges because the sun's gravitational effect adds to the moon's rather than opposing it. The moon is the primary tide-generator (its effect is about twice the sun's), but the sun produces meaningful tides too. When the sun and moon are aligned at new and full moons, their tidal bulges overlap and reinforce each other. The result is higher high tides (water gets pulled up more strongly) and lower low tides (more water is pulled away from the in-between regions). Total range can be 20-50% larger than average.
What makes them different from regular tides?
Spring tides differ from average tides primarily in range, not in their daily cycle. They still have two highs and two lows per day, separated by about 12 hours 25 minutes. The difference is the magnitude: high tides are noticeably higher and low tides noticeably lower than usual. Beaches show more exposed sand at low tide and water reaches further up the shore at high tide. Coastal navigation channels can become more or less navigable. The pattern is so predictable that tide tables routinely show when spring tides will occur.
How often do spring tides occur?
Spring tides occur approximately every two weeks, alternating with neap tides (which occur at the moon's quarter phases). The exact interval is half a synodic lunar month (the time between successive new moons), about 14.77 days. Some calendar months have three spring tide periods (those long enough to fit them in); most have two. The strongest spring tides (called king tides) occur a few times per year when spring tides coincide with the moon's closest approach to Earth (perigee), producing exceptionally high water levels.
A spring tide is the largest tidal range of the lunar cycle, occurring at new and full moons when the sun and moon align with Earth. The combined gravitational effects produce higher highs and lower lows than usual. Spring tides happen roughly every two weeks. The strongest spring tides (king tides) occur when they coincide with the moon's closest approach to Earth.
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