Tides

Science

Definition

The regular rise and fall of ocean water levels caused primarily by the gravitational pull of the Moon and, to a lesser extent, the Sun. Most coastlines experience two high tides and two low tides roughly every 24 hours and 50 minutes.

Examples

  • The Bay of Fundy in Canada has the world's highest tides, with water levels changing over 16 meters
  • Spring tides occur during full and new moons when the Sun and Moon align, producing extra-high tides
  • Tide pools along rocky coastlines are exposed at low tide, revealing sea stars and anemones
Key Fact

Spring tides (highest) occur at new/full moon; neap tides (lowest range) occur at quarter moons.

Related Terms

Earth-moon system Universal gravitation Ocean currents

Study This Concept

Practice tides with free review games in these units:

Earth Science Unit 5: Oceans and Water