Volcanic eruptions. Slumping of sediments piled on the continental shelves down the continental slope. Meteorite impacts. Other underwater explosions including detonations of underwater nuclear devices. They do not resemble normal sea waves, because their wavelength is far longer.
They initially resemble a rapidly rising tide, for which reason they are often wrongly referred to as tidal waves. Owing to the enormous wavelength the wave oscillation at any given point takes 20 to 30 minutes to complete a cycle and has an amplitude of only about 1 m. This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage underneath.
When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Since the waves still have the same very long periods, they may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break, but rather appears like a fast-moving wall of water.
Tsunami waves hitting the coast of Minamisoma in Fukushima prefecture, Japan. Photo taken March 11, , by Sadatsugu Tomizawa. Tsunami wave heights of tens of meters can be generated by large seismic events. Although they affect the entire ocean, their destructive power in coastal areas is enormous.
Tsunami waves resulting from the earthquake in the South China Sea killed an estimated 40, people. In northern Chile more than 25, people were killed by tsunami waves in Waves as high as 7 m were recorded in the Caribbean, across the Atlantic Ocean. According to the U. National Oceanic and Atmospheric Administration NOAA , the Pacific is the most active tsunami zone, but tsunami waves can be generated in other bodies of water including the Caribbean and Mediterranean Seas, the Indian and Atlantic Oceans and in inland lakes.
The Indian Ocean tsunami — a series of devastating waves, with heights up to 30 m — was caused by a magnitude 9. It is reckoned among the deadliest natural disasters in human history, inundating coastal communities in 14 countries bordering the Indian Ocean and killing , people.
Other hazardous waves can roll upon the shore like a massive sea level rise and fall, and can reach far inland are caused by tides, and are discussed later in this article.
For a more detailed discussion of these and rogue waves in the oceans, see the article Waves in Atmospheric and Oceanic Systems. Tides are very long-period waves, occurring once or twice a day, which move through the oceans in response to the gravitational forces exerted by the moon and sun.
Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface. The appearance of a high tide corresponds to the crest of a tidal wave reaching a particular location.
A low tide corresponds to the lowest part of the wave, or its trough. The difference in height between a high tide and low tide is called the tidal range. When tides are channeled between islands or into bays and estuaries, they are termed as Tidal Currents. A flow tid e or a flood tide is a rising tide or incoming tide which results in a high tide. Ebb Tide is the receding or outgoing tide. It is the period between high tide and low tide during which water flows away from the shore.
The regular interval between two high or two low tides is 12 hours 25 minutes. The highest tides in the world occur in the Bay of Fundi in Canada. While both the Moon and the Sun influence the ocean tides, the Moon plays the biggest role because it is so much closer to our planet than the Sun.
Spring Tides: Occur when the sun, earth and moon are in a straight line. This happens twice every lunar month — once when the sun and the moon are on the same side of the earth new moon , and again when they are on opposite sides full moon. Neap Tides: Occur seven days after a spring tide when the sun and moon are at right angles to each other with respect to the earth, thus countering the gravitational pull exerted by each over the earth.
Neap tides are thus lower than spring tides and also occur twice in a lunar month — during the first and third quarter moons. Diurnal tidal cycle. Semidiurnal tidal cycle. Mixed Semidiurnal tidal cycle. Distribution of tidal cycles along the coastlines of the world.
Since the orbits of the earth and the moon are elliptical, their distances from the earth vary continuously, resulting in variations in the magnitude of tides. When the moon is at perigee closest to the earth , unusually high or low tides occur. When it is at apogee furthest from the earth , the tidal range is much less than normal. Likewise, unusually high or low tides occur when the earth is at perihelion closest to the sun , while their range is small when the earth is at aphelion furthest from the sun.
These impede navigation and cause mixing of coastal waters. Breaking internal waves and tidal currents are a major force driving oceanic mixing. Tidal mixing helps drive the deep circulation, and influences both short- and long-term climate change.
Tidal currents generate internal waves over seamounts, continental slopes, and mid-ocean ridges, causing agitation of ocean bottom sediments, so that they become suspended in the deep oceans. Accurate knowledge of tides is needed for computing the orbit of altimetric satellites and for correcting altimeter measurements of oceanic topography.
Apart from basic curiosity, the rise and fall of tides play an important role in the natural world, having a marked effect on maritime activities.
They are different to other currents in that they are generated by tidal flows and are, therefore periodic and predictable. There are additional currents generated by other factors such as wind or thermohaline circulation a convection driven by salinity and temperature of the ocean.
Thermohaline currents are found at all depths of the oceans. Ocean currents are harder to predict although pilot books have been compiled over time and the approximate position, direction and speed of ocean currents can be estimated dependent on the time of year. In some locations, such as the Strait of Gibraltar, we have tables which show us tidal streams and the surface current flowing into the Mediterranean from the Atlantic.
Obtaining this information is useful as it allows individuals to direct cargo ships safely, determine the extent of an oil spill and best fishing spots, allows for tsunami tracking and aids in environmental restoration activities. Rate this post! Email This Post : If you like this article or our site. Please spread the word. Difference between waves, tides and currents. Difference Between Similar Terms and Objects.
MLA 8 Naidoo, Shalinee. Amazing explanation!! There is more than enough information about waves, tides and currents. This is very helpful, appreciate this work. Name required. Email required. Please note: comment moderation is enabled and may delay your comment. There is no need to resubmit your comment.
Notify me of followup comments via e-mail. Written by : Shalinee Naidoo. User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. Waves Waves are defined as the movement of water that occurs on the surface of water bodies like oceans, seas, lakes and rivers.
What influences waves? Types of waves There are many different types of waves such as capillary waves, ripples, seas and swells and they can manifest in a range of shapes and sizes, such as small waves or big swells that can travel over long distances. Tides Tides are formed as a result of centrifugal force and the gravitational attraction between the Earth, Moon and Sun and are often characterised by movements of water over extended periods of time [1].
What influences tides? Types of tides Tides are categorized according to the number of high and low tides formed as well as their relative heights and as such can be classified as being semi-diurnal, diurnal or mixed. Currents The large masses of water moving in a specific direction from one location to another are known as currents. What influences currents? Conclusion Tides, waves and currents are completely different. Table 1: Waves Tides Currents Formed due to the forces exerted by winds on the water surface Formed due to the interaction of gravitational forces between the Earth, Sun and Moon Formed as a result of temperature differences on oceanic surfaces Waves are defined as the energy that moves across the surface of the water Tides are defined as the rise and fall of the sea level Currents are defined as the direction of flow of a body of water The intensity of waves are influenced by wind factors The intensity of tides are influenced by the location and position of the Earth The intensity of currents are influenced by winds, temperature differences in water and the oceanic surface topography Waves occur regularly across bodies of water Tides occur twice a day Equatorial currents like El Nino occur every few years Waves move from side to side Tides move up and down Currents flow clockwise in the Northern Hemisphere and counter clockwise in the Southern Hemisphere.
This is known as the Coriolis Effect. Author Recent Posts.
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