Understanding the Nature of Tides - Report Example

Tides Introduction Tides de periodic elevation and falling of the average sea level, which takes place in the ocean. On a daily basis, the ocean edges slowly shift seaward and landward as the ocean level falls and rises. Understanding tides is of significance in various coastal activities such as fishing, tide pooling, surfing, navigation, and shell collection. Tides are of great significance such that, for several centuries, nearly every port has kept accurate records. However, it was not until the development of universal law of gravitation by Sir Isaac Newton (1642–1727) that the world received the real facts about tides (Giordano, 2012). This essay tries to create an understanding of tides through elaborating their causes, the wave motion, and the categories of tides and tidal currents. Causes of Tides In the Pacific Ocean, for instance, the ocean water intrudes the shoreline and floods the bays and estuaries twice daily. It floods marshes and mud flats, elevates water levels, and flows landward with a force enough to reverse the creeks’ and rivers’ seaward currents. The salty water mingles with the fresh water and for some hours the brackish brew briefly relaxes to deposit important nutrients, which feed numerous organisms living in the intricate estuarine system. The process is then reversed when the estuary is flushed by the receding waters carrying inorganic and organic materials including potentially dangerous pollutants out to the ocean. These periodic and predictable movements of sea waters are the tides. Simplistically, the gravitational force experienced by the Earth from the Sun and Moon results to ocean tides. Generally, the forces imposed on the Earth generate tides. This forces result from combination of motion and gravity among the Sun, the Earth and the Moon. The gravitational law asserts that, in the universe, two bodies always attract each other. The mass of these bodies and the distance between them determines the strength and magnitude of the attraction (Pugh, 2007). The Sun is approximately 390 times far from Earth and its mass is 27 million times the mass of Moon. Therefore, despite the Sun affecting ocean tides, the gravitational attraction exerted by the Moon on Earth is greater because of the Moon’s proximity to the Earth. Actually, the Sun’s effect is approximately 45% of the Moon’s effect (Giordano, 2012). To understand tides, one can consider the Earth to be an egg-shaped body having its long axis focused on the moon. Assume a deep ocean completely covers the Earth such that the Earth’s watery surface bulges towards Moon. On Earth’s opposite side, a similar bulge is created by centrifugal force. These are considered the high tides. Two simultaneous and corresponding low tides happen at equivalent distances around Earth amid the high tides. Actually, tides work this way, however, nature is hardly ever perfect or ideal. The great diversity of the topography of the Earth including other extraterrestrial and terrestrial effects makes ocean tides to vary in many ways and to have certain comparisons. Further, tides normally go almost unnoticed on open seas because the high tides are merely 2-3 feet above the low tide. However, tides may vary greatly along the coast depending on certain influences, particularly topography. In some regions of the world, measurements for the tidal difference range amid successive low and high waters is done in inches, while in other regions a dramatic disparity can exist. For instance, in Nova Scotia at Fundy Bay, the difference amid the low and high water can even be more than 50 feet. The mean disparity amid low and high water along the Oregon coast is approximately 5-6 feet. At times of extreme tides, especially June and December, the range of the tides can double this or can be approximately 10-12 feet (Souchay, Mathis & Tokieda, 2013). Wave Motion According to Souchay, Mathis and Tokieda (2013), understanding tides also involves examining the wave propagation mechanism in the ocean since tides are in the form of waves. This is also significant in understanding tidal bores and tidal currents. Often, the crest is a wave’s high point (top) and the trough is its low point (valley). Description of waves is made by their: 1) Length (L) – horizontal distance between crests, 2) Height (H) – vertical distance from a crest (mid part) to a trough (mid part). One half of H is amplitude (A), 3) Period (T) – time interval amid two successive crests’ occurrence at fixed point, and 4) Speed/Celerity (C) – L divided by T i.e. C = L / T; expressed in distance / unit time. The transformation of wave and their internal workings in shallow water can be understood better through following a swell from the open sea to the shore. Wind waves moving out of a wind generating region or altered direction of the generating region or continue after wind has subsided is what is referred as a swell; progressive waves. In the ocean, despite every wave form moving in distance, the particles of water which create the wave never move. Water particles that create waves under the crest move in a similar direction as wave form, while under the trough these particles move in an opposite direction. Half way amid the crest and the previous trough, the next crust is formed through water moving up one-quarter after a period. Half way amid the crest and the next trough, water moves down to create a trough one-quarter after a period. Therefore, in one wave period, water particles forming the wave illustrate circular orbits. A swell in open sea is considered deep water waves; the bottom never affects them. The diameter of these orbits logarithmically decreases with depth. In reality, a slight overlap exists in these orbits resulting to a net mass water movement in the waves’ direction. This ensures an elevation to the long-shore and the rip current system, which is vital in the removal of accumulated water in the surf zone. The net mass movement can become especially important in high wave situations that accompany severe storms like hurricanes (Giordano, 2012). In case a swell moves into water that has a depth less than approximately half their wave lengths then the circular orbits experience a restriction from the bottom; these orbits become elliptical. The orbits tend to become more elliptical as water progressively becomes more shoal. This happens until the particulate movement is back and forth. Generally, tidal waves are shallow water waves. In other words, the tidal wave’s length is much longer than depth. Thus, the particulate movement that creates the wave is merely back and forth. The back and forth particulate movement is known as the tidal current. Often, people confuse tide or tidal waves with tsunamis. Tides and Tidal Currents Foing (2007) asserts that in most parts of the Earth, in a day, there exist two low tides and two high tides. These tides follow a cycle, which corresponds with the lunar day (24- hour 50- minute), the time Earth takes to finish a rotation relative to Moon. Along the coasts of Americas Atlantic two low and high tides happen every day with relatively small disparity amid successive low and high waters. These tides are referred to as semi-diurnal. A diurnal tide exists in the Mexican Gulf (north shore), to mean it travels in and out but only once a day. In Pacific Northwest, mixed tides are experienced; two lows and two highs a day, typified by noteworthy difference amid successive tides. A flood tide or flood current is tidal flow that is incoming while an ebb tide or ebb current is an outgoing tidal flow. When little current exists, the period between ebb and flood tides is referred to as slack tide or slack water. Foing (2007) further comments that the Moon apart from having the greatest effect on tides, also affects the character of the tides. Every month as the Moon creates an elliptical orbit around Earth, it semimonthly aligns with the Sun and the Earth, during the new-moon and full-moon phases. At such moments, tides become either extremely low or extremely high. These are the spring tides (not related to the season of spring). Amid these phases, during the first and third quarters of the Moon, the Moon is at right angles with the Sun. The gravitational interaction is counterbalanced by this position of the Moon and Sun leading to a period where the range amid low and high tides becomes minimal. These are the neap tides. Pugh (2007) adds that in certain situations, tidal currents and other currents usually conflict and at times generate hazards to boaters, surfers, and swimmers. In the bays’ and estuaries’ partial enclosures and coastal rivers’ mouths currents regularly run over and churn. Sometimes opposing currents occur along the open sea beaches, particularly next to headlands and artificial structures like breakwaters and jetties. Places having clustered islands near rugged mainland in a manner that narrow passages are created, tides usually create turbulence. Strong, subsurface tidal current conflicting with another tidal current leading to a violent disturbance under the water, often in a direction opposing that of surface water is denoted as a riptide. Riptides can occur where no noticeable surface commotion exists, despite it appearing as a calm or dark paths navigating through breakers. In contrast, a tiderip readily appears on the surface. This simply is a stretch or rip of turbulent water at the ocean in a strait or bay generated by a tidal current traveling in a rough bottom or conflicting tidal currents. Tiderips can materialize as slightly choppy stretches in water moving beside glassy-calm water. They may also look like whitewater rapids between otherwise calm seas. Conclusion Generally, scrutiny of the causes of tides, the wave motion, and the categories of tides and tidal currents creates a quick understanding of tides. Studying the causes of the tides acts like the initial step in the understanding of tides and how they impact the coastal environment. In addition adequate knowledge of tides and their impacts is vital for community planning and development, recreation, navigation and also our survival. Further, understanding tides makes the coastal regions more fascinating for visitors and residents. Individuals with knowledge on various types/categories of tides and tidal currents can easily enjoy tidewaters and tidelands in safety and comfort. References Foing, B. (2007). If We Had no Moon. Astrobiology Magazine, 55, 893-896. Retrieved from http://www.astrobio.net/topic/exploration/moon-to-mars/if-we-had-no-moon/ Giordano, N. (2012). Collage Physics: Reasoning and Relationships. NY: Cengage Learning. Pugh, D. (2007). Changing Sea Levels: Effects of Tides, Weather and Climate. Heidelberg: Springer. Souchay, J., Mathis, S., & Tokieda, T. (2013). Tides in astronomy and astrophysics. Heidelberg: Springer. Read More