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Category Our World

When was the longest heatwave?

The longest heatwave ever recorded was in Marble Bar, Australia when the temperature stayed above 38 . It lasted for 162 days from 23 October 1923 to 7 April 1924.

The highest average annual temperature recorded is 34.4  in Dallol, Ethiopia.

The lowest recorded temperature (outside of the poles) was -68  in Verkhoyansk, Siberia, on 6 February 1933.

The lowest average annual temperature of -56.6  was recorded at the Plateau Station, Antarctica.

Fact File:

Some living things have adapted to survive long periods of time without water. Plants such as cacti have the ability to conserve water. They also minimize water loss as they have no leaves, and photosynthesis takes place in the stem. They have roots which reach deep into the ground for water.

 

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When do we see mirages?

Mirages form in hot deserts where the air is so hot it bends and distorts light rays. The shimmering images that a mirage produces have often tricked travellers in deserts. People think that they can see an oasis or town on the horizon, but in reality it is not there.

Under certain conditions, such as a stretch of pavement or desert air heated by intense sunshine, the air rapidly cools with elevation and therefore increases in density and refractive power. Sunlight reflected downward from the top of an object. When the sky is the object of the mirage, the land is mistaken for a lake or sheet of water.

Fact File:

About one-third of the world’s land surface is covered by desert. Deserts are found wherever there is too little water to allow much plant life to grow. Salt deserts form when shallow seas and lakes dry up, leaving a deposit of smooth salt.

 

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When did weather forecasting begin?

People have been able to forecast the weather for hundreds of years. Meteorologists have used simple instruments like thermometers, rain gauges, barometers and wind gauges for many years, but with the arrival of satellite photography, weather forecasting has been transformed. With the use of computers, increasingly accurate forecasting is now possible.

Traditional forecasters have been known to use pine cones, which open and close according to the humidity of the air. An open cone is supposed to mean dry weather. Seaweed also responds to changes in humidity. Dry seaweed indicates dry weather.

Fact File:

There is an old saying regarding the weather: if the oak tree has its leaves before the ash then it will be a fine summer.

 

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When is a barometer used?

A barometer is used to measure the changes in air pressure. Air pressure varies across different parts of the Earth’s surface, and these differences cause winds. Air moves from an area of high pressure, or an anticyclone, to an area of low pressure, or a depression. Depressions are usually associated with worsening weather conditions and rain. In a mercury barometer the air pressure pushes down on the mercury, which is forced up the barometer to give an accurate reading.

Air pressure is greatest at sea level, where it amounts to 14.7 pounds a square inch. It is greatest there because that is the bottom of the atmosphere. At highest altitudes the pressure is less.

Fact File:

The higher we go the less air pressure there is. This is the reason that space suits and the cabins of high-flying planes are pressurized. They are designed to maintain the air pressure our bodies must have.

 

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When do fog and mist arise?

It is tiny water droplets condensing from moist air that cause fog and mist to rise. The water droplets can occur at ground level. The air can only hold a limited amount of water. If the air suddenly cools, its capacity to hold water is reduced, which results in a mist or fog.

When fog develops, visibility can be affected quite badly. Mist is less dense. It often occurs on calm, clear nights when heat rises, forming a thin layer of mist close to the ground. Mist often forms over water because a mass of warm air passes over a cold stretch of water.

Sometimes visibility is affected in built up areas due to mist and fog, but this is sometimes mistaken for smog. Smog is a buildup of exhaust fumes and factory smoke which hangs over the area until a huge amount of air movement can blow the smog away.

Fact File:

Fog particles are small, less than 1/25,000 of an inch in diameter. When you have a dense fog and can’t see in front of you, it is because there may be as many as 20,000 of these particles in one cubic inch.

 

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When do monsoons occur?

A monsoon is a season of very heavy rain falling is tropical countries. Monsoons are most common near the Equator. They occur when seasonal winds spring up carrying moist air in from the sea. Important crops such as rice depend entirely on the monsoon season to provide the right growing conditions.

If the monsoon rains fail, famine often follows. There are also some special winds called monsoon winds. These are winds that change their direction with the season. In India, the monsoons blow south as hot, dry winds in the wintertime, and blow north in the summer, bringing heavy rainfall.

Fact File:

The Aborigines believe that if a possum is left cooking by the water’s edge, a sizzling sound is produced. The noise irritates the rainbow snake, who they believe crawls underground towards the source of the noise. As it moves along, the weather turns stormy, and the monsoon rains begin.

 

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When was the top of Mount Everest first reached?

Mount Everest, which is in the Himalayas, is 8,863 metres high. At these altitudes, mountains are always covered in snow and ice, and there is little oxygen to breathe. Mount Everest was finally conquered on May 29, 1953, when a Nepalese guide, Tenzing Norgay, and a New Zealander, Edmund Hillary, reached the highest point on the Earth’s surface. Since then, many people have climbed Everest, and all the world’s major peaks have now been conquered.

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Mountain peaks are often seen to be surrounded by layers of cloud. This is because as winds laden with water are blown towards the mountains, they are forced to rise and the temperature drops. The water condenses into clouds at these higher altitudes.

 

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When are mountains formed?

Mountains can be formed in three different ways. Volcanoes form mountains when lava from deep inside the Earth cools and hardens on the surface.

Other mountains are formed when two plates move towards each other under pressure or where an oceanic plate is pushed under a continental crust. The pressure causes the ground near the joining plate margins to fault and fold. The ground is forced upwards to form mountains. The Rockies, Alps, Andes, Urals and Himalayas were all formed in this way.

Finally the Earth’s crust can fracture and create faults which mean that large blocks of land can be moved upwards or downwards. Faults in the rocks normally occur when there is a lot of pressure on the rocks. Mountain building is a slow process and happens over centuries.

Fact File:

Rock slides are common where forests have been destroyed on mountainsides. There are no longer any tree roots to stabilize the loose material.

 

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When was the worst volcanic eruption?

The island of Krakatau, Indonesia (west of Java) was a small volcanic island. The volcano itself had laid dormant for over 200 years until August 1883. On May 20 one of the cones erupted violently and three months later the whole island blew up. It was the biggest explosion in recorded history. For two and a half days the island was in total darkness because of the amount of dust in the air. A cloud of ash rose 80 km into the air. The eruption caused a tidal wave which killed 36,000 people. The explosion could be heard and felt in Australia, 3,500 km away.

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On August 24 in the year AD 79, there was a great eruption of Mount Vesuvius, a volcano in southern Italy. The lava, stones, and ashes thrown up by the volcano completely buried two nearby towns.

 

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When are volcanoes dormant?

The word dormant actually means ‘sleeping’. So when people talk about a volcano being dormant, it really means it is temporarily sleeping and might erupt at any time in the future. An extinct volcano, on the other hand, is one that will not become active again. Like earthquakes, volcanoes mainly occur along fault lines. Earth’s crust to release the pressure that has built up. When there is very little pressure the volcano can remain in a dormant state for many, many years. On the island of Maui there is a volcano called Haleakala which rises to a height of about 10,025 feet. It is the world’s largest inactive volcano. Its crater is about 20 miles around and some 2,720 feet deep.

Fact File:

A major volcanic eruption can hurl boulders high into the air. These boulders, called volcanic bombs, can be very large indeed.

 

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