Which tide term describes two highs and two lows per day?

• A. Diurnal tide
• B. Semi-diurnal tide
• C. Neap tide
• D. Slack tide

Answer: (B)

Semi-diurnal tides produce two highs and two lows each day. This pattern happens because the Moon and Sun create two tidal bulges on opposite sides of the Earth, so as a coastlines moves through those bulges you experience a high tide when you’re under a bulge and a low tide in between. The cycle repeats roughly every 12 hours 25 minutes, giving two highs and two lows in about a 24-hour period. Slack tide is just the brief lull between tides when water movement slows, not the number of tides per day. Neap tide refers to a phase with a smaller tidal range during quarter-moon alignments, again about amplitude rather than frequency. A diurnal tide would have only one high and one low per day.