THE TERRESTRIAL ENVIRONMENT- EARTH MOVEMENTS AND THEIR EFFECTS

LAND AND SEA BREEZES

Land and sea breezes are actually convection currents (remember convection from temperature control). During the day, the land heats up more rapidly than the sea, hence the heated air rises from the land and an area of relatively lower pressure is formed, Sea breeze begins to blow from the sea towards the land to replace the rising air.

However, as the land loses heat more quickly and becomes cooler than the sea at night, the opposite occurs. Land Breeze blows from the cooler land (area of high pressure) towards the warmer sea (area of lower pressure).

TYPES OF AIR MASSES An air mass is an extremely large, uniform body of air with a relatively constant temperature that develops over a certain region. Air masses may be cold or warm and humid or dry.

Ø Air masses are classified according to their areas of formation, or source regions. Air masses can be classified as: Artic (A), Antarctic (AA), Polar (P), Tropical (T) or Equatorial (E).

Ø Artic or Antarctic air masses are extremely cold, polar air masses are cold, tropical air masses are warm and equatorial air masses are extremely warm.

Ø Air masses are also classified by the type of surface (ocean or land) over which the air masses are formed: Maritime (m) for ocean surface and Continental (c) for land surfaces.

Ø Air masses can move from one region to another due to differences in air pressure. As air masses bring along their characteristics (temperature or humidity) as they move, the movements of air masses might lead to weather changes.

Ø Moving air masses can bring pollutants from one region to another. For example dust from as far as Africa (Sahara dust) can be transported to the Caribbean. In another example, the movement of air masses led to the spread of radioactive fallout from the 1986 Chernobyl disaster in Ukraine to many parts of Europe and even the United States.

Ø At the boundary zones where bodies of air masses with different properties meet one another, weather changes commonly occur. These transitional regions are called fronts.

TYPES OF LOCAL FRONTS

There are four main types of local fronts:

1. A cold front occurs when a denser cold air mass advances into an area of lighter warm air mass. The heavier cold air mass is forced under the warm air mass, causing the warm air to rise, cool and condense to form clouds that usually form rain. A strong cold front can cause thunderstorms and even tornadoes.

2. A warm front occurs when a lighter warm air mass approaches a denser cold air mass. The warm air rises over the cold air and produces less severe weather such as light rain. In general, warm fronts move slower than cold fronts.

3. An occluded front occurs when a faster moving cold front follows and catches up with a slower moving warm front. An occluded front is generally characterized by continuous rain.

4. A stationary front occurs at the boundary between two air masses where neither the cold air mass nor the warm air mass is advancing. There will be a noticeable difference in temperature between one side of the stationary front and the other side of the stationary front. If the stationary front starts moving, it will become either a cold front or a warm front depending on the direction of movement.

CHARACTERISTICS OF A HURRICANE

• Hurricanes (also known as typhoons and cyclones) are a system of intensive low air pressure.

• It is the extreme form of a tropical storm with extremely strong winds of over 64 knots. Hurricanes form within the trade wind belt over warm tropical oceans of at least 27°C.

• Low vertical wind shear (changes in wind direction and speed over altitude) aids the growth of hurricanes

• Hurricanes are usually found between the latitudes of 5° to 30° North and South of the Equator. They generally do not form within 5° because the Coriolis force is too weak nearer the Equator.

• The Coriolis force is an apparent force arising from the Earth’s rotation. It causes storms to rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

• As a hurricane travels over an ocean, it will suck in warm and moist air that will further increase its strength. The moisture that is picked up by the hurricane will be released as an extremely heavy downpour. On reaching land or colder ocean waters, the hurricane will weaken and gradually die off.

• Hurricanes are classified in categories from category one hurricanes (mildest) to category five hurricanes (most severe).

TSUNAMI AND TIDAL WAVES

Tsunami is a huge wave that is usually generated by an underwater disturbance, such as an underwater earthquake, a submarine volcanic eruption or an underwater landslide. For example, an underwater earthquake results in the sudden movement of the ocean floor, which displaces water, thus causing a tsunami. Tsunamis are commonly referred to as “tidal waves” which can be misleading as tsunamis are not related to the tides. As tsunami waves approach shallow waters, friction with the sea bed increases, so the waves will slow down. There will be a decrease in the wavelength and an increase in the wave height. Even though there is a decrease in the speed of the waves, the huge energy of the waves remains the same and can cause widespread devastation.

VOLCANIC ERUPTIONS A volcano is formed when magma (hot molten rock) is forced out from the mantle onto the Earth’s surface in the form of flowing lava. Volcanoes can be classified as active, dormant or extinct based on their level of activity. Active volcanoes are volcanoes that are still erupting, have erupted recently or are showing signs of possible eruption in the near future. Dormant volcanoes are volcanoes not currently erupting and have not shown any signs of unrest over a period of time, but may still erupt in the future. Extinct volcanoes are volcanoes that have not erupted for an extremely long time and are unlikely to ever erupt again. Types of volcanoes: Volcanoes can be classified according to their shapes and their vents.

1. A fissure volcano occurs when lava flows out through an open fissure at a constructive plate boundary instead of a central vent. The lava of a fissure volcano is usually runny basaltic lava, leading to the formation of a relatively flat plateau.

2. A shield volcano is a type of central volcano. Runny basaltic lava is ejected from

a central vent to form an extensive mountain with gentle slopes. An example of a shield volcano in Mauna Loa in Hawaii.

3. A strato or composite volcano is another type of central volcano and it tends to

be associated with more violent eruptions. Both lava and volcanic ashes are ejected from a central vent, and sometimes through secondary vents that may be found along the slopes of the volcano. An example of this kind of volcano is Mount Vesuvius in Italy and Mount Fuji in Japan.

4. A caldera is an enlarged depression that is formed when the old summit of a

volcanic cone is removed by the collapse of a volcano into itself. After an eruption the empty magma chamber can no longer support the weight of the volcano and it collapses. A caldera can be filled with water to form a crater lake e.g Crater Lake in USA.

Consequences of volcanic eruptions:

• Lava (fluid mixture of hot gases, ashes and rock) flow can cause massive damage to land and vegetation.

• Ecosystems can be destroyed by lava flow and blankets of volcanic ash. For example the eruption of Soufriere in Montserrat resulted in coral bleaching.

• A volcanic eruption can trigger off a tsunami. For example a tsunami generated by the eruption of Krakatoa of Indonesia in 1883 killed 36,000 people.

• Volcanic gases like sulphur dioxide are given off during an eruption and can contribute to the formation of acid rain.

• Volcanic eruptions may affect the global weather and climate. Volcanic ashes in the atmosphere can block out sunlight and cause temperatures to drop.

MEASURING EARTHQUAKES Earthquakes are detected and measured using a seismograph, which is a device that can detect seismic waves by recording the vibrations from an earthquake. When an earthquake occurs, the faster moving primary (P) waves will be the first to be recorded by the seismograph, after which the slower secondary (S) waves with greater amplitude will be recorded. By measuring the time interval between the P waves and the S waves, seismologists can calculate the approximate distance between the epicenter of the earthquake and the seismograph.

The Richter scale is commonly used to measure the magnitude (strength) of an earthquake. The Richter magnitude scale, also known as the local magnitude (ML) scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude (shaking amplitude) of the largest displacement from zero on a particular type of seismometer (Wood–Anderson torsion). So, for example, an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.

Richter magnitudes Description Earthquake effects Frequency of

occurrence

Less than 2.0 Micro Microearthquakes, not felt. About 8,000 per day

2.0-2.9 Minor

Generally not felt, but recorded. About 1,000 per day

3.0-3.9 Often felt, but rarely causes damage. 49,000 per year (est.)

4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely.

6,200 per year (est.)

5.0-5.9 Moderate

Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings.

800 per year

6.0-6.9 Strong Can be destructive in areas up to about 160 kilometres (100 mi) across in populated areas.

120 per year

7.0-7.9 Major Can cause serious damage over larger areas. 18 per year

8.0-8.9 Great

Can cause serious damage in areas several hundred miles across. 1 per year

9.0-9.9 Devastating in areas several thousand miles across. 1 per 20 years

10.0+ Epic Never recorded; see below for equivalent seismic energy yield.

Extremely rare (Unknown

The earthquake in Haiti in January 2010 was recorded as 7.0 on the Richter scale. The relationship between earthquakes and volcanoes:

Ø Both earthquakes and volcanoes are commonly found along plate boundaries. For example the Pacific Ring of Fire is a zone associated with frequent earthquakes and volcanic eruptions.

Ø Although both earthquakes and volcanoes can occur at destructive plate boundaries (convergent) and constructive plate boundaries (divergent), usually only earthquakes occur at conservative plate boundaries (transform) where two tectonic plates slide past each other.

FORMATION OF TIDES Tides refer to the position at which waves hit the shore. Tides are the regular rising and falling of the oceans’ surface due to the tidal force of the Moon and the Sun. The highest level is known as “high tide” and the lowest level as “low tide”

1. High and Low Tides: Even though the mass of the Moon is a lot smaller than that of the Sun, its tidal force exerts a greater effect on the oceans than that of the Sun’s because it is closer to the Earth. The tidal force of the Moon pulls the water on the side of the Earth that is closest to it, resulting in a high tide. At the same time, another high tide will occur on the opposite side of the Earth. Also, two points of low tides will occur at positions 90° from the direction of the Moon.

2. Spring Tides: Twice in a lunar month, during the new moon and full moon, The

Sun and the Moon are in alignment, and so the gravitational force of the Sun adds on to that of the Moon. This results in the high tide being higher than usual and the low tide being lower than usual. This phenomenon is called the spring tides.

3. Neap Tides: During the first quarter and third quarter of the Moon, neap tides are formed. During these phases the Sun and the Moon are at right angles to each other. This results in some of the gravitational effect of the Moon on the ocean being cancelled by that of the Sun, as their gravitational forces are pulling at the oceans in different directions. The high tides are lower than normal and the low tides are higher than normal.

Neap Tides Effects of the Tides:

Ø Tidal patterns can affect the feeding behaviors of animals. Algae and seaweed (food for first order consumers) are washed up onto the shores during high tides. The feeding patterns of some animals coincide with the tides. For example the Mummichog fish feeds mainly during high tides when they are in the marsh.

Ø Mating behaviors of certain animal species are also influenced by the tides. For

example the Grunion fish mate and lay their eggs during the high point of a spring tide. The Horseshoe Crabs also mate during the spring tides, and migratory birds such as Red Knots appear in large numbers during these periods to feed on the eggs of the Horseshoe Crabs.