Ocean waves are rhythmic up-and-down motions on the water’s surface. These movements represent a transfer of energy through water, not the water itself traveling long distances. While water particles move in a circular motion, the wave form, or energy, progresses across the ocean.
Wind’s Role
The most common ocean waves are generated by wind interacting with the water’s surface. Wind transfers energy to the water through friction and pressure, creating an initial disturbance that builds. This process begins with small ripples and progresses into larger waves as the wind continues to blow.
Several factors influence the size and characteristics of wind-generated waves. Wind speed is a primary factor; stronger winds generally produce larger waves. Duration, or how long the wind blows, also plays a role, with longer durations leading to bigger waves. Fetch, the distance over open water that the wind blows consistently, contributes to wave growth. Large waves form when these three factors—wind speed, duration, and fetch—combine effectively.
Wind-driven waves vary based on their development. Capillary waves are the smallest ripples, formed by wind and affected by surface tension. As wind energy increases, these develop into gravity waves, which are larger and more common, with gravity becoming the dominant restoring force. Swells are waves that have traveled away from their generating area, appearing as smooth, rounded waves that can travel vast distances across ocean basins.
Waves from Geological Activity
Tsunamis originate from large-scale displacement of water, typically due to geological activity. Underwater earthquakes are the primary cause, particularly those in subduction zones where one tectonic plate slides beneath another. When these plates suddenly slip, they can cause the seafloor to uplift or subside, displacing the overlying water.
Other geological events can also trigger tsunamis, including large underwater landslides, volcanic eruptions, or even meteorite impacts. Tsunamis differ significantly from wind-generated waves. They possess extremely long wavelengths, often hundreds of kilometers in the deep ocean, compared to typical wind waves which are around 100 meters.
Tsunamis travel at very high speeds across deep oceans, comparable to a jet airplane, often unnoticed at sea due to their small height. As they approach shallower coastal waters, their speed decreases, but their height increases substantially, forming a wall of water or a rapidly rising tide. This destructive power near coasts allows tsunamis to inundate large areas.
Tidal Forces
Tides are a different type of wave, characterized by the periodic rise and fall of sea levels, caused by the gravitational pull of celestial bodies. The Moon’s gravitational force is the primary influence on Earth’s tides, with the Sun also contributing. This gravitational attraction causes the Earth’s water to bulge outwards on the side closest to the Moon and, due to inertia, on the side farthest from the Moon.
These tidal bulges represent areas of high tide. As the Earth rotates through them, coastal areas experience the cyclical rise and fall of water levels. Tides are considered extremely long-period waves, with wavelengths spanning thousands of kilometers across ocean basins. Unlike wind waves or tsunamis, tides are driven by predictable astronomical mechanics rather than atmospheric or seismic events, making their patterns forecastable.