What natural phenomenon is categorized by significant changes in water levels influenced by gravitational forces?

The significant changes in water levels influenced by gravitational forces are known as tides. Tides are primarily caused by the gravitational pull of the moon and the sun on the Earth’s oceans. As the moon orbits the Earth, its gravitational force causes the water in the oceans to bulge out in the direction of the moon, leading to a rise in water level, known as a high tide. Conversely, on the side of the Earth opposite the moon, there is also a high tide due to the inertia of the water.

This cyclical nature of tides occurs roughly every 12 hours, resulting in predictable patterns of rising and falling water levels. Because tides operate on a much larger scale than other phenomena, such as currents or slack water, their classification as a natural phenomenon driven by gravitational forces is distinct and well-documented in oceanography.

The other options refer to different oceanographic terms: flood currents and ebb currents are related to the movement of water caused by tides (flood current indicates water moving towards land and ebb current indicates water moving away), while slack water refers to the brief periods when the water is still between incoming and outgoing tides. However, these currents and slack water do not directly denote the significant changes in water levels caused specifically by gravitational influences