Waves, especially ocean waves, are often so common that we never usually think about where they come from or how they’re formed. In this article, you’ll be diving into the specifics of the formation of waves, including the various types of waves and where you may find them.
Depending on the type of wave, there can be various reasons why they’re formed. While most waves, such as those we typically see out in the ocean, are caused by energy transfer within the water (brought on by wind), others may be formed by factors such as underwater disturbances, severe weather, or gravitational pull.
From here on out, you’ll be taking a closer look at each type of wave, along with the reasons for their formation. Each type will be separated into its subheadings to simplify readability.
What are Waves?
Before going into detail on the different types of waves and how they’re formed, it's best to have a clear understanding of what waves are in general so that the processes discussed later make sense.
As discussed earlier, waves are primarily formed by energy traveling through the water, which happens to be the medium in this case. Depending on the medium, there are many other types of waves (i.e., electromagnetic and sound waves).
In all cases, waves transfer energy, not the medium itself, meaning if nothing is in its way, the waves can potentially travel through the whole ocean.
This movement of energy is what causes waves to move in a circular motion.
Below is a general overview of an ocean wave. It details the anatomy of a wave, including the crest (highest point) and trough (lowest point), which will be mentioned several more times throughout the article.
What are Wind-Driven/Surface Waves?
Wind-driven waves, otherwise known as surface waves, are the types of waves we’re most familiar with. These waves are the ones that travel continuously along the surface of the ocean until they eventually break over land.
In the cases of these waves, the wind is the source of energy that, while traveling across the water, creates friction that eventually develops into a wave crest.
These waves can be found in either smaller lakes or across the open oceans (and their coasts) around the world.
Small Capillary Waves are Born
Wind-driven/surface waves begin as capillary waves (wavelengths are below 1.7 cm), which are small ripples on the water surface due to slight breezes. The capillary waves provide a source of friction as the wind “grips” onto them and creates larger waves, known as wind waves.
When these small waves are first formed, you have either the surface tension (of the water) or gravity (when the waves are larger) acting as a restoring force to return the water to its calm state.
Wind Increases in Speed, Creating Larger Waves
When the energy of the wind increases, three factors then come into play that determine the amount of energy and, thus, the overall size of the waves: the wind speed, duration, and the distance over which the wind blows in a straight line.
Regardless of which factor increases, the overall amount of energy moving through the water increases, and thus, the speed and size of the waves increase as well.
However, wind-generated waves can only reach a certain size. As the waves grow larger due to increasing energy transfer, they become steeper as well.
Unlike wind-driven/surface waves, there are a few other types of waves that are much rarer to see as they only form under specific conditions. However, these waves are usually also much more powerful as they typically contain significantly more energy behind them.
Here, you’re presented with two types of hazardous waves, storm surges and tsunamis, which will be presented first in general and then specifically at their formation processes.
What are Storm Surges?
Storm surges are a series of long waves (waves with long wavelengths) that are formed in the deep waters far from shore. These waves, though starting mild and far from land, can intensify rapidly as they get closer inland, causing a significantly dangerous rise in sea level.
Storm surges, per their namesake, occur due to the presence of strong storms and other severe weather phenomenon, such as hurricanes. The surges are due to the strong winds and pressure that accompany storms, the former of which can push water onshore.
Many factors, such as the orientation of the storm track relative to the shoreline, the attributes of the storm (intensity, speed, size, etc.), and bathymetry (the depth of the water), go into play when determining the approximate amplitude/severity of a storm surge.
When measuring storm surges, we look at how high the tide has gone over its normal predicted astronomical tide, meaning that anything above the normal tide level can be considered part of a storm surge. When you combine the two types of tides, you get the total observed seawater level, otherwise known as the storm tide.
Because astronomical tides are highest during a new or full moon (details of which we’ll look at later), the highest storm tides are observed when there’s a powerful storm during a new or full moon.
What are Tsunamis?
Another potentially even more devastating and usually much larger type of wave that is also quite rarely seen is tsunamis.
Tsunamis are caused by various types of disturbances (typically underwater, such as earthquakes or underwater volcano eruptions, but sometimes also caused by landslides) that displace a tremendous amount of water. This causes the water to then spread out and away from the epicenter in a continuous series of waves.
You can picture what the phenomenon looks like if you imagine the ripples that occur when you toss a pebble into a pond. Just like how the ripples spread out and away from the place where the pebble hit the water, tsunamis also move in a similar pattern except, of course, on a much larger scale.
Like storm surges, tsunamis start mild out in the far ocean but become gradually more intense and higher as they approach land, where the ocean becomes shallower.
The waves’ speed depends on the ocean’s depth instead of how far the waves have traveled from the epicenter.
In this case, the speed of the waves is inverse to ocean depth, meaning the deeper the ocean is, the faster the waves travel, and vice versa. And, of course, when the waves slow down, the amount of energy gathered over the entire distance will fall onto a much smaller volume, becoming the extremely high waves we usually associate with tsunamis.
Both tsunamis and storm surges are the types of waves that rapidly roll onto shores like enormous sea level rises, as opposed to the typical wind-driven waves we see that crash down onto the shores.
What are Gravitational Waves?
The final type of wave discussed in this article is gravitational waves, otherwise known as tidal waves or just tides for short.
The reason for these waves is due to the sun and moon’s gravity pulling on the Earth’s surface. It’s because of this that people can accurately predict the rise and fall of these waves depending on the time of day.
Because tidal waves are dependent on the gravitational pull of much larger and farther away objects, their periods (the time needed for a wave to travel its entire length) and wavelengths are also much longer. They originate in the ocean and travel towards the shore throughout the day, where they’ll look like the rise and fall of the ocean surface.
Depending on which part of the wave hits the shore, people may see it as either high tide (at the wave’s crest) or low tide (at the wave’s trough), with the range between the two being the tidal range.
Although people often don’t think much of waves as they repeatedly come crashing onto the shores, there is quite a large variety of them, each with their own form and formation process. Hopefully, this article has proven just how much of the natural world there still is to discover around us.
Written by Edward Zhang
Edward is an accomplished author with a deep passion for the ocean. He holds a masters in marine science degree at the University of New South Wales and a bachelors in biology from Stony Brook University.
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