A tidal cycle of two high tides and two low tides each lunar day, with the high tides of nearly equal height.

Study for the IB Marine Science Standard Level Exam. Prepare with interactive quizzes and in-depth explanations. Use our resources to excel in your marine science knowledge!

Multiple Choice

A tidal cycle of two high tides and two low tides each lunar day, with the high tides of nearly equal height.

Tides come in different patterns based on how the Moon’s gravity and the Sun’s gravity interact with the rotation of Earth. When a coast experiences two highs and two lows each lunar day and the two high tides are about the same height, that pattern is semidiurnal. The ocean bulges on the side of Earth facing the Moon and on the opposite side, and as Earth rotates, a given location moves under each bulge roughly twice per ~24 hours 50 minutes, producing two highs and two lows per lunar day. If the two highs were noticeably different in height, it would be a mixed tide. Neap and spring tides describe shifts in the overall tidal range due to the Moon’s phase (neap = smaller range, quarter moons; spring = larger range, new/full moons) but don’t define the pattern of how many highs and lows occur.

A tidal cycle of two high tides and two low tides each lunar day, with the high tides of nearly equal height.

Study for the IB Marine Science Standard Level Exam. Prepare with interactive quizzes and in-depth explanations. Use our resources to excel in your marine science knowledge!

A tidal cycle of two high tides and two low tides each lunar day, with the high tides of nearly equal height.

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