Introduction
Tidal waves and tsunamis are both phenomena that occur in the sea. If you live near coastal areas, you might have experienced a tidal wave at some point (they happen every day). Tsunamis are less common but more calamitous.
Tidal Waves vs Tsunamis
Tidal waves and tsunamis are both water wave-based phenomena. Tidal waves occur due to the gravitational forces of the sun and moon. They happen every day (two highs and two lows). There are three types of tidal wave patterns semidiurnal, mixed-semidiurnal and diurnal. They usually appear near coastal areas. Tidal waves move with a speed of 16 to 32 kilometres per hour, and their size can range from a few millimetres to meters. Since they are an everyday natural phenomenon, tidal waves do not cause any damage. However, sometimes the waves can read up to 16 metres, and these can cause flood damage.
Tsunamis, on the other hand, are drastically different. Tsunamis happen due to geographical disturbances like earthquakes, landslides, volcanic eruptions etc. If it disturbs the tectonic plates, it could lead to the rise of a tsunami. Tsunamis can happen anywhere with a large enough water body with the correct causal factors. They race at 800 kph. Tsunami sizes vary from mico-tsunami to mega-tsunami. Tsunamis can cause devastating damage to lives, buildings, etc.
Difference between Tidal Wave and Tsunami in Tabular Form
| Parameters of Comparison | Tidal Wave | Tsunami |
| Cause | Gravitational forces of sun and moon | Geological disturbances |
| Location | Coastal areas | 80% happen in the Pacific Ocean. |
| Size | Ranges between a few millimetres to a few meters | Ranges from 150 to 1000 km |
| Frequency | Everyday | Depends on geological disturbances |
| Speed | 16 to 32 kph | 800 kph |
What are Tidal Waves?
In simple terms, a tidal wave is a wave caused by tides. Tides are the periodic rise and fall of an ocean's surface water. When a high tide rises fast enough to take the form of a wave, it can cause a tidal wave. Tidal waves occur because of the gravitational pull of the sun and moon. Therefore, it is during the full moon and new moon that extremely high tides occur. If the moon is in a quarter position, it causes low tides.
Causes of tidal waves
In essence, tidal waves happen due to the gravitational pull of the sun and the moon. The closer the Earth is to the sun or moon, the greater the tidal waves. The moon is more impactful because it is much nearer to the Earth than the sun. The high tides take place during the full moon and the new moon. During these times, the sun, the moon, and the Earth are all on the same line. This position results in a sizable gravitational force and hence the high tides. In contrast, when the moon is in its quarter phases, the waves caused by gravitational forces are lowest.
The tides caused by the sun's gravitational force are called solar tides. The tides caused by the moon's gravitational force are called lunar tides. At the time of the full moon and the new moon, the lunar and solar tides amalgamate and create higher and lower tides known as the "spring tide." A week later, the sun and moon will be at a right angle relative to each other. This position means the gravitational pull occurs from different directions. As a result, the high tides caused by the solar tide will be lower, and the low tides caused by the moon will be higher. In other words, there is barely any height difference between the high and low tides. This tide phenomenon is called "neap tide."
Types of tidal waves
Around 29% of the Earth's surface is land. This amount of land area means the ocean waves cannot freely flow around. Since their path is blocked, the ocean tides create intricate patterns within each ocean basin that differ from one another.
- Semidiurnal tide- is when an area has two high tides and two low tides. High tides are the same height, and low tides are the same height. Usually found on the East Coast.
- A mixed-semidiurnal tide- is when an area has two high and low tides. The two high tidal waves are of different heights, the same for low tides. Usually found on the U.S. West Coast.
- Diurnal tide- is when a water body has only one high and low tide. An example would be the waves found in the Gulf of Mexico.
Other features of tidal waves
- Location- Tidal waves happen in coastal areas. Verbosely tidal waves are created when the amount of water is enough to be affected by the gravitational forces of the sun and moon.
- Speed- A normal tidal wave moves at 16 to 32 km/h.
- Frequency- Daily. Coastal areas experience two high tides and two low tides daily.
- Size- The location and tidal circumstances affect the size of the tidal waves. Their sizes vary from a few millimetres to meters in height.
Aftereffects of a tidal wave
Usually, a tide wave does not cause any damage. It is a regular occurrence in the water body. The only damage it causes is soil erosion along the shore.
Sometimes, a tidal wave rises to 16 meters and is very intense. These tidal waves can cause flooding and affect the houses situated on beaches.
What is Tsunami?
Like tidal waves, tsunamis are also phenomena that occur in water bodies. Tsunamis were called tidal waves in the past. But this is a misnomer. Unlike tidal waves, tsunami is not affected by tides, they are not affected by the sun and moon, and they do not break. Alternatively, they occur as a result of seismic events. Several prior geographical works mention the phenomenon as "seismic waves."
A tsunami comprises numerous waves with powerful currents, behaving like fast-rising tides. A tsunami can have a varying duration from several hours to several days.
Causes of Tsunami
A tsunami chiefly occurs due to a geographical event that disturbs the ocean.
- Tectonic plate shifts resulting in earthquakes
- Volcano eruption
- Erupting submarine
- Any gas bubble eruption occurring in the ocean
- Landslides
- A meteor strike to the ocean
When these seismic disturbances occur deep within the ocean, the surface water body rises or falls. This movement creates waves with a wide-ranging wavelength, eventually becoming a tsunami.
How does an earthquake lead to a tsunami?
For an earthquake to end with a tsunami, it must fulfil a few requirements. One, it should be an event large enough to displace the sea floor. Two, Thrust earthquakes cause more earthquakes than strike-slip earthquakes.
- An earthquake with a magnitude below 6.5 doesn't result in a tsunami.
- An earthquake with a magnitude between 6.5 to 7.5 can cause changes in the sea level. However, these won't lead to disastrous tsunamis.
- An earthquake magnitude between 7.6 to 7.8 can cause calamitous tsunamis near the epicentre.
- An earthquake magnitude of 7.9 or higher can lead to catastrophic local tsunamis. It also leads to significant changes in the sea level. Further, it can cause damage to the shores. If the earthquake occurs with a magnitude of 9.0, it might lead to an aftershock of 7.5 or higher.
Qualities of tsunamis
- Location- 80% of tsunamis take place in the Pacific Ocean. However, a tsunami can happen anywhere with a large water body and the correct causal agents.
- Speed- The geographical events strong enough to cause a tsunami also releases massive amounts of energy. This energy contributes to the pace of tsunamis. A tsunami can achieve a speed of 800 kilometres per hour.
- Frequency- It is not possible to accurately predict the occurrence of tsunamis. It depends on the circumstances of its causal factors. From 2000 BC to 2007, 2275 total tsunamis happened.
- Size- Tsunamis have a varying number of wavelengths and amplitudes. It can be small as a micro-tsunami, which needs sensitive instruments on the ocean floor to be noticeable. Alternatively, it can be a mega-tsunami, which can disrupt the coastlines. Usually, the wavelength of tsunamis measures between 150 and 1000km.
Aftereffects of tsunami
Typically a tsunami has a wavelength of up to 200km and a speed of 800 kph. When the waves reach the land masses, their momentum decreases, and their amplitude (wave height) increases swiftly.
The size and quality of tsunamis mean they can cause extensive damage when they reach land. It will drown anything in its way. It can cause floods and soil erosions. It destroys houses and building on the shore, destroying entire villages. The greatest calamity caused is when tsunamis take the lives of humans and animals. Throughout its history, tsunamis have caused the death or injury of thousands of people.
One way to combat the effects of tsunamis is to plant thick, strong trees that can withstand the force of tsunamis along the shore.
Some other terms associated with tsunamis
- The Shaoling Effect- When tsunamis occur in the middle of oceans, it doesn't cause any damage and are usually unnoticed. But this is not the case when tsunamis occur near coastal areas. The water levels near coastal areas are shallower. Ergo, when tsunami waves reach these shallow waters, they slow down, and their amplitude increases. Sometimes the waves can reach a height of about 30 meters. This event where a tsunami becomes more dangerous because of shallow water is called the shoaling effect.
- Wave Train- It is a series of waves developed from a tsunami. These waves can be of different heights and occur one after the other. Tsunami waves with high water levels are called crests. Tsunami waves with low water levels are called troughs. Crests and troughs can happen anywhere and with a time difference of 10 to 45 minutes between one another. They can even appear days after the tsunami wreaked havoc.
The scales used to measure tsunamis
- Sieberg scale- it was the first ever measuring scale used for tsunamis, developed by Sieberg in 1927. It is a descriptive 4-grade scale.
- Sieberg-Ambraseys scale- In 1962, N. Ambraseys modified the Sieberg scale into a 6-grade scale. The Sieberg-Ambraseys scale measures tsunamis in the Mediterranean Sea.
- Tsunami Magnitude Scale- In 1942, A. Imamura developed a 5-grade descriptive scale.
- Imamura-Lida intensity scale- In 1963, K. Lida modified the tsunami magnitude scale and added a grade for measuring weak tsunamis. This scale measures tsunamis in the Pacific Ocean.
- ML scale- is a magnitude-type scale developed by T. Mrty and H. Loomis.
- Tsunamograph- The National Oceanic and Atmospheric Administration (NOAA) of the United States invented the "tsunamograph." This device provides real-time data on tsunamis. The tsunamograph comprises a seafloor recorder and a buoy. The seafloor recorder is situated at a depth of 5000 meters to measure variations in the water level. The buoy acts as the receiver for the seafloor recorder. It picks up the acoustic signals from the seafloor recorder and transmits them to the satellites. These signals contain information about the heights of waves, which can predict the occurrence of tsunamis.
Main Differences between Tidal Waves and Tsunamis (In Points)
- Tidal waves occur due to the gravitational forces of the sun and moon. Tsunamis happen due to geographical disturbances.
- Tidal waves occur near coastal areas. Tsunamis can happen anywhere with a large enough water body.
- A tidal wave moves at 16 to 32 km/h. A tsunami has a speed of 800 kph.
- Tidal waves occur every day. Tsunamis happen when there is a seismic disturbance.
- A tidal wave ranges between a few millimetres and a few metres in size. A tsunami wavelength can range between 150 to 1000 km.
- Tidal waves do not cause damage. Tsunamis are calamitous. They can destroy buildings, drown people and animals and cause excessive soil erosion.
Conclusion
In short, tidal waves and tsunamis are two very different water phenomena. While tsunamis were referred to as tidal waves in the past, this is a misnomer. Instead of gravitational forces, tsunamis happen due to seismic disturbances. Tidal waves are regular occurrences and range from a few millimetres to a few meters. They don't cause any damage. By comparison, tsunamis are not common occurrences. They range between 150 to 1000 km. Tsunamis can cause extensive damage.
References
- https://a-z-animals.com/blog/tsunami-vs-tidal-wave-key-differences/
- https://www.worldatlas.com/articles/what-are-the-differences-between-tidal-waves-and-tsunamis.html
- https://www.sms-tsunami-warning.com/pages/tsunami-features#.ZDO07nZBzIU
- https://oceanservice.noaa.gov/education/tutorial_tides/tides06_variations.html#:~:text=When%20the%20sun%2C%20moon%2C%20and,both%20commonly%20called%20spring%20tides.
- https://www.exploratorium.edu/theworld/surfing/suntides.html
- https://www.scienceandthesea.org/program/201110/lunar-and-solar-tides
- https://oceanservice.noaa.gov/education/tutorial_tides/tides07_cycles.html
- https://www.usgs.gov/faqs/what-difference-between-a-tsunami-and-a-tidal-wave#:~:text=and%20unrelated%20phenomena.-,A%20tidal%20wave%20is%20a%20shallow%20water%20wave%20caused%20by,the%20ocean%2C%20volcanic …
- https://www.usgs.gov/faqs/what-are-tsunamis
- https://www.usgs.gov/faqs/what-it-about-earthquake-causes-a-tsunami
- https://tsunamicommission.ipma.pt/wp-content/uploads/workshop2007/gusiakov.pdf
