Can Violent Sea Storms Damage the Ocean Floor?
It's a common curiosity whether violent storms at sea, such as hurricanes, can cause damage to the ocean floor. The answer is yes, but the extent and nature of this damage can vary depending on the storm's intensity and the depth of the water.
Understanding the Impact of Storm Waves on the Ocean Floor
Geologists have observed a distinctive crossbedding pattern known as "hummocky bedding," which forms as storm waves mix sediments at the ocean floor. This phenomenon is particularly evident in nearshore marine environments, defined as the 'shoreface' area, which is further divided into upper and lower segments. The upper shoreface encompasses the shallow areas affected by "fair-weather" surf, while the lower shoreface, being deeper, is only impacted during severe storms.
Wave Base and Wave Energy
Wave energy has a minimal effect on the ocean floor at the greatest depths. Conversely, it has the most impact in shallow waters. The 'wave base' is defined as the depth to which surface waves can reach the bottom. Typically, this depth is roughly half the wavelength of the surface wave.
The relationship between waves and the ocean floor is complex, depending on the wave height and period (the distance from one crest to the next). Larger waves, with greater periods, can travel deeper before affecting the ocean floor, and vice versa. As waves approach shallower water, their energy is dissipated, causing them to slow, become steeper, and eventually break. This process not only reshapes the seafloor but also stirs up sediments and can move rocks, gravel, and even break coral.
Wave Dynamics and Their Impact on the Ocean Floor
The transition from deep-water waves to shallow-water breaking waves represents a critical phase where significant changes occur. Referring to this source for a detailed explanation, let's explore how these waves interact with the seafloor.
Deep-Water Waves
Deep-water waves are characterized by traveling across a body of water where the depth is greater than half the wavelength (D 1/2L). These waves include all wind-generated waves in the open ocean.
Transitional Waves
Transitional waves occur in water where the depth is less than half the wavelength but greater than one-twentieth the wavelength (1/20L ≤ D 1/2L). These waves, often wind-generated, move into shallower water.
Shallow-Water Waves
Shallow-water waves are defined as waves traveling in water where the depth is less than one-twentieth the wavelength (D 1/20L). These include wind-generated waves in nearshore areas, tsunamis, seismic waves from ocean floor disturbances, and tide waves from the gravitational attraction of the sun and moon.
Breaking Shallow-Water Waves
Shallow-water waves begin to break when the ratio of wave height to wavelength is 1:7 (H/L 1/7), when the wave's crest is steep at less than 120 degrees, or when the wave height is three-quarters of the water depth (H 3/4D). Deep-water waves also break under similar conditions, especially when seas are confused or the wind causes whitecaps.
Understanding these dynamics helps in recognizing the complex interactions between waves and the ocean floor, which can lead to significant reshaping and stirring of the seafloor during severe storms. Geologists studying these phenomena can use this knowledge to better understand coastal and marine environments and predict the effects of future storms.