How many high and low tides occur each day?

How many high and low tides occur each day?

• A. 2
• B. 1
• C. 3
• D. 4

Answer: (A)

Tides on most coastlines follow a semidiurnal pattern, producing two high tides and two low tides each day. The Moon’s gravity creates two bulges in the oceans—one toward the Moon and one on the opposite side of Earth. As Earth rotates, a given coastline moves through these bulges and through the troughs between them, so it experiences a high tide when aligned with a bulge and a low tide when between bulges. This cycle repeats roughly every 12 hours, with about 12 hours and 25 minutes between successive highs (and between successive lows). The Sun also affects tide heights, making spring and neap tides, but it doesn’t change the typical count per day. In some places you can have one high and one low per day (diurnal) or more irregular (mixed) tides, but two highs and two lows per day is the common pattern.

Tides on most coastlines follow a semidiurnal pattern, producing two high tides and two low tides each day. The Moon’s gravity creates two bulges in the oceans—one toward the Moon and one on the opposite side of Earth. As Earth rotates, a given coastline moves through these bulges and through the troughs between them, so it experiences a high tide when aligned with a bulge and a low tide when between bulges. This cycle repeats roughly every 12 hours, with about 12 hours and 25 minutes between successive highs (and between successive lows). The Sun also affects tide heights, making spring and neap tides, but it doesn’t change the typical count per day. In some places you can have one high and one low per day (diurnal) or more irregular (mixed) tides, but two highs and two lows per day is the common pattern.