TIDES - ADVANCED PHYSICAL GEOGRAPHY

TIDES – ADVANCED PHYSICAL GEOGRAPHY

Tides are the periodic changes in the elevation of the sea/ocean surface. OR

Tides are regular periodic alternating rises and fall of the level of water in the ocean. Behavior of ocean tides is the result of comprehensive study done by British physicist named Sir Isaac Newton. The ocean tides commonly occur twice in 24 hours.

TIDAL CONCEPTS

i. High tides (HT)

This is the highest elevation of tides as the sea water rises on shore, often sometimes the high tides is accompanied with the storm surges. During high tides the shore and beach are covered by sea water.

ii. Low tides (LT)

This is the lowest level of elevation reached by ocean and sea water. It is marked by retreat of sea water. During the low tides the shore and the beach are clearly exposed as water reaches.

iii. Tidal range

This is also called as tidal amplitude. It is the difference in height between the high tides and low tides. Tidal ranges in the open ocean is low (1 or 2 feet’s) but in a shallow marginal sea and in estuary is very high (30-40 feet’s).

iv. Tidal currents

This is the alternating horizontal movement of sea/ocean water associated with the rise and fall of the water. The forward movement of currents towards the shore submerging the low-lying coastline is flood tidal current and that backward movement exposing the sea shore is called Ebby tidal currents.

v. Tidal flat

This is marshy or muddy area that is alternatively covered and uncovered by rise and fall of tides depending on the nature of the coast. Tidal flat varies in size from narrow stripping sea wards of the beach to the extensive shore they may extend for several kilometer

CAUSES OF OCEAN TIDES

The ocean tides resulted from the following causes. These are: –

i. Gravitation forces of the moon and sun.

These forces deform the ocean causing it ot move body in alternatives way i.e rise in some place and fall in some place. Effect of moon is very great because of its closer to the earth. Therefore, the gravity decreases as the distance increases.

The moon exerts gravitational pull, hence the water of the earth’s surface facing the moon is attracted and pulled hence high tide occurs. The high tides also formed at the opposite side of the earth simultaneously because of the reactionary forces (centrifugal) of the gravitational (centripetal) forces of the moon causing out wards bulge of water.

ii. Earth rotation.

Both earth and moon rotate and revolve in same direction i.e anticlockwise direction as a result of shifting of the ocean as it bulges in different places to follow intensity of the gravitational pull. Therefore, every part on the earth’s surface experiencing two high tides and two low tides during lunar day with interval 0f 12 hours and 26 minutes between each tide.

The earth takes 24 hours to rotates on its axis and 27.3 days for moon to rotate on its own axis with the same period revolve around the earth.

iii. Shape of the coastline.

Generally tidal currents are speedy and cover the shore at shorter time on estuaries and bays. This is the because tidal waves advance up channel more in constrict and shallow shore than in open sea shores.

CLASSIFICATION OF OCEAN TIDES

There are different criteria of classifying the ocean tides like as follow;

i. Categories of tides according to height or degree of tidal range.

ii. Categories of tides according to rate of frequency occurrence per day.

iii. Categories of tides according to gravitational force.

iv. Categories of tides according to moon distance from the earth.

I: CATEGORIES OF TIDES ACCORDING TO HEIGHT OR DEGREE OF TIDAL RANGE.

In this category, there are two types of tides. These are;

a) Spring tides (Syzygy tides);

What is the syzygy?

Is the position of the sun, moon and earth in a straight line.

What is the conjunction?

Is the position when sun and moon are in one side of the earth (the situation of solar eclipse).

What is the opposition?

Is the position of the earth is in between the sun and moon (position of solar eclipse).

What are the spring tides?

Are the very high tides which occur when the sun, the moon and the earth are almost in the same line i.e during full moon and new moon periods.

The spring tides occurs when moon and sun are in the same alignment, they reinforcing the gravitational pull of the moon on the earth example during solar and lunar eclipses. When this occurs, gravitational attraction increases and producing the highest high tides and lowest low tides with maximum tidal ranges. It is occurring twice a month i.e during full moon and new moon, its characterized with unusually high or low tides.

b) Neap tides (Quadrature tides);

What is the quadrature?

Is the position when sun, earth and moon are in right angle position.

What are the neap tides?

Are the tides which occur sun, earth and moon at right angles position. The force of gravity from the moon and the sun pulling the water to themselves. When it occurs, the high tides become lower than normal and low tides become higher than normal with low tidal ranges especially when occur with apogeal tides. It is very common during first and third quarter of the moon. It occurs twice a month i.e at half-moon.

II: CATEGORIES OF TIDES ACCORDING TO RATE OF FREQUENCY OCCURRENCE PER DAY.

In this category, there are three types of tides. These are;

Diurnal tides;

This tides characterised by having one high water rise (HT) and one water fall (LT) during each 24 hours. It is very common in the North Gulf of Mexico and South East Asia.

Semi-diurnal tides;

These are tides with two tidal rises and two tidal falls during each day. It occurring approximately after every 12 hours. The high tides attractive more the same level oa the low tides. They are common in the equatorial regions especially in the Atlantic Ocean.

Mixed tides;

These are tides with two high and two low level of water per day but different amplitude.

They may reveal inequalities in the high tides while the low tides remain constant or vice versa. These tides are common in the Pacific and Indian Ocean

III: CATEGORIES OF TIDES ACCORDING TO GRAVITATIONAL FORCE.

In this category, there are two types of tides. These are;

Solar tides;

These are tides produced by the influence of gravitational force from sun to the earth. These tides are low tidal ranges because of the furthest distance of the sun from the earth which affect gravitational attraction to be low. However, when coincide the lunar tides they form high tidal ranges.

Lunar tides;

These tides formed due to influence of the gravitational force of the moon to the earth.

They are greatest rise with high tidal ranges since, the moon is very close to the earth.

IV: CATEGORIES OF TIDES ACCORDING TO MOON DISTANCE FROM THE EARTH.

In this category, there are two types of tides. These are;

a) Perigeal tides;

What is the perigee?

Is the period in the orbit of the moon when the moon is nearest to the earth.

What are the perigeal tides?

Are the tides occurring when the moon is nearest to the earth hence its tides producing effects are more powerfully due to the high intensity of gravitational attraction. If these tides considered with spring tides the high tidal ranges occur. The high tide become high than the normal and low tides become low than the normal. b) Apogeal tides;

What is the apogee?

Is the period when the moon at the farthest position from the earth.

What are the apogeal tides?

Are the tides which occurs when the moon is at farthest distance from the earth as it revolves around it. Hence intensity of gravitational attraction is very low and the tides are lower than the normal. If these coincides with neap tides the tidal ranges become very low.