My Science School

What are ‘highs’ and ‘lows’?

Air pressure varies across different parts of the Earth’s surface, and this difference causes 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. These changes in air pressure can be measured by an instrument called a barometer. In a mercury barometer the air pressure pushes down on the mercury, which is forced up the barometer to give an accurate reading. 

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Why do we get thunder and lightning?

Lightning is a huge spark of electricity that is produced in a cloud. Thunder is the loud noise made by the lightning as it rips through the air.

During thunderstorms, enormous electrical charges build up inside a cloud. Eventually the charges seem to flow down to the ground when lightning strikes. In fact, the electrical charges flow up from the ground and down from the cloud at the same time. The tremendous heat generated by the lightning causes the explosive noise of thunder. Lightning frequently strikes in the same place repeatedly, and along the same path through the air. It can also strike between two clouds.

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Thunderbolts

A lightning strike discharges about 100 million volts of electricity, and heats the air in its path to more than 33,000°C.The lightning strike travels at 299,792 km per second, which is almost the speed of light. A strike between a cloud and the ground may be 14 km long, and a strike between clouds can be over 140 km long.

Ball lightning is a small fiery ball which occasionally appears during thunderstorms. There is no accepted scientific explanation for it. 

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How can forecasters predict the weather?

Meteorologists use a wide range of instruments and techniques to help them track changes in the weather and to predict future weather conditions. Weather forecasters have used simple instruments such as thermometers, rain gauges, barometers and wind gauges for many years, but the advent of satellite photography has transformed weather forecasting. Weather satellites can track the movements of clouds, and show the positions of high and low pressure areas and weather fronts. Radar measures the size, speed and direction of storms, so accurate warnings of severe weather can be given. With the use of computers, increasingly accurate forecasting is now possible.

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What causes mist and fog?

Tiny water droplets condensing from moist air cause both mist and fog. They can occur at ground level. The air can only hold a limited amount of water vapour. If the air suddenly cools, its capacity to hold water is reduced, resulting in mist or fog. When fog occurs visibility can be affected. Mist is less dense. It commonly occurs on calm, clear nights when heat rises, forming a thin layer of mist close to the ground. 

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How are hailstones formed?

Hail is produced when particles of ice bounce up and down inside a cloud. In cold temperatures, water droplets inside a cloud will freeze into small pellets of ice. As these begin to fall, they may meet warm air rising, which carries them back up into the cloud. There they cool once more, and the process is repeated. As more and more water freezes onto their surface, the ice pellets gradually grow in size. Eventually they become so heavy that they fall to the ground as hailstones. Some hailstones are as big as a clenched fist and can do serious damage to buildings and livestock. 

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What is a monsoon?

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

 

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What is smog?

Smog is a serious form of air pollution that can cause breathing problems. The term smog was first used to describe a type of air pollution in London, when smoke from coal fires combined with fog to produce dense yellow clouds that sometimes persisted for days. The term now describes the hazy fog that is caused mainly by vehicle exhausts and smoke from factories. It builds up when there is little air movement, and can happen when a layer of warm air traps cooler air near the ground, preventing the smog from being blown away. Cities in bowls or sheltered valleys are particularly liable to this condition. 

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Who studies the weather?

People called meteorologists study the world’s weather and the changes in the atmosphere that produce our weather. They observe and analyze the weather, and try to understand the processes that lead to changing weather conditions. The study of weather is known as meteorology. 

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Why does rain fall?

Water evaporates from the Earth’s surface, condenses into water droplets and falls back down to the ground as rain. Heat from the Sun causes water to evaporate from the land, from rivers and lakes and from the sea. The water vapour rises with the warm air, and eventually reaches high altitudes where it cools and condenses into water droplets, forming clouds. The droplets grow larger until they are too heavy to stay in the cloud and they fall as rain. Rain usually falls from the largest and darkest clouds, which contain the most water vapour. 

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Why do geysers spout hot water?

When water seeps through the ground and reaches magma, hot rock or volcanic gases, it boils violently. This produces steam that can shoot the water out of cracks, causing a geyser. Geysers can be very spectacular, and some shoot water as high as 500 m into the air, although most are much less powerful. Sometimes they erupt at regular intervals, but most erupt only occasionally. 

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What happened when Krakatoa erupted?

The eruption of Krakatoa, in Indonesia, in 1883 was the biggest explosion in recorded history. Krakatoa was a small island between Java and Sumatra, on which there was a small cluster of volcanoes that were not dangerously active. On May 20, 1883, one of the cones erupted violently, and three months later the whole island blew up. The explosion could be heard in Australia, 3,500 km away, and a cloud of ash rose 80 km into the air. For two and a half days the island was in total darkness because of the amount of dust in the air.

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Volcanic bombs

A major volcanic eruption can hurl boulders high into the air. These boulders, called volcanic bombs, can be very large. Most of the material thrown out of the erupting volcano is ash, which forms a huge cloud. Steam and sulphurous gases are also released, and these can be very dangerous to bystanders. Pumice is a kind of foamed rock that is often thrown out during an eruption. It is full of tiny holes, making it very light. It is formed when gases in molten rock are boiled off; creating foam that solidifies as it cools. 

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What is the Ring of Fire?

All around the rim of the Pacific Ocean is a circle of places of volcanic activity known as the Ring of Fire. The Ring of Fire is caused by shifts in the giant plates that make up the Earth’s crust. The Pacific plate is gradually disappearing under the surrounding continental plates, and volcanic activity marks the points where this movement is taking place. Frequent earthquakes accompany the volcanic action in the countries surrounding the Pacific. Also, ocean trenches and underwater volcanoes form around the Ring of Fire. 

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What is lava?

Lava is molten rock that reaches the Earth’s surface. Its temperature may be as high as 1, 200 degree Celsius. Lava may be as runny as water or so thick that it scarcely moves at all. The liquid type of lava that flows from Hawaiian-type volcanoes runs downhill in sheets and streams, travelling very fast. Sometimes the surface of these streams cools and hardens, and the liquid lava continues to flow underneath, eventually producing lava tubes when it cools. The thicker type of lava inches its way down the side of a volcano like a very slow avalanche, carrying with it anything in its path, as well as red-hot lava. 

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What happened to Pompeii and Herculaneum?

Two busy Roman towns were completely buried in lava and ash by an eruption of Mount Vesuvius in AD 79.

A burning rain of ash, lava and volcanic debris covered Pompeii to a depth of more than 3 m. Nearby Herculaneum was buried under about 18 m of ash. Many people were overcome while trying to escape the eruption. In Pompeii, cavities were found in the ash where their bodies had lain and then rotted away. The two towns preserved everyday Roman life, and they are still being excavated. 

 

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What is a volcano?

Volcanoes are openings in the Earth’s crust through which molten lava, red-hot rocks, steam and fumes pour out. We usually think of a volcano as a smoking mountain that erupts explosively, but most volcanoes are simply cracks in the crust through which lava flows continuously.

The more familiar kind of volcano has a single central pipe though which lava reaches the surface, building up into a cone as it cools. The cone consists of layers of lava and volcanic ash. There is usually a crater at the centre. Most active volcanoes smoke and spit out occasional pieces of lava, and dramatic eruptions are rare.

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How fast do volcanoes grow?

Unlike most geological happenings, the growth of a volcano can be very rapid. In 1943, a farmer in Mexico noticed smoke coming from a crack in the ground in his cornfield. Lava began to ooze out, and six days later it had piled up into a volcanic cone 150 m high. By the end of the year the cone had grown to 450 m. The eruption finally stopped in 1952, when the volcano Paricutin had reached a height of 2,808 m above sea level. The volcano had buried two whole villages. 

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How can rocks be folded up?

Most rocks are too brittle to be reshaped, but folding is common in sedimentary rocks. Movements in the Earth’s crust force flexible sedimentary rocks into folds. These folds are sometimes so large that the rock lays back on itself in layers. Geologists may find that the layers of rock are actually upside down, with the youngest rocks on top. 

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What is a mountain range?

A group of mountains is called a range. Nearly all large mountains are grouped in ranges. Single high peaks are usually old volcanoes. Mount Kilimanjaro in Tanzania is the highest mountain in Africa. It is a single peak, and is an extinct volcano. These isolated peaks always look much higher than mountains in ranges, because they are not surrounded by the usual lower foothills that disguise their true height.

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Why do clouds form near mountains?

Clouds form when damp air is forced upwards to pass over a mountain range. Air is forced up the face of the mountain because it is unable to go around it. There is usually a high wind on the top of the mountain. As it rises, the air becomes cooler and the moisture in the air condenses to form water droplets, resulting in the formation of clouds. This explains why there is often high rainfall and snow in mountainous regions.

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What is a rockslide?

Rock is broken away from the mountainside by the effects of freezing. Rainwater enters cracks in the rock and as it freezes, it expands and opens the crack wider. As the thaw begins the pieces of rock splinter and separate from the bedrock. Loose rock builds up continuously on a mountainside, but usually only small pieces slide down. This loose broken rock is called scree.

A rockslide takes place when the mass of broken pieces of rock slides down the side of a mountain. This usually happens in very wet weather, when rain lubricates the rock and allows it to slide freely down the mountainside, mixed with a torrent of mud.

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Are climbers able to breathe at high altitudes?

The higher you climb, the thinner the air becomes, until there is not enough oxygen to support life. On the highest mountains, there is just about enough oxygen for life to survive for a short time. Extremely fit mountaineers have managed to climb to the top of Mount Everest without the use of oxygen cylinders.

Our bodies can adapt slowly to a lack of oxygen, which is why expeditions to the Himalayas and other high ranges camp at progressively higher levels to get used to the thinner air. People living at high altitudes in the Andes and the Himalayas develop enlarged chests and changes in their lungs to help them breathe.

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What is chalk?

Chalk is formed from the skeletons of millions and millions of tiny animals called foraminifera. It is a sedimentary rock that formed millions of years ago beneath shallow seas. Chalk is used in the manufacture of rubber goods and paint. 

 

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Which are the highest mountains in the world?

The world’s highest mountains are in the Himalaya-Karakoram range to the north of India. The Andes Mountains in South America cover a larger area but are not so high. The Himalayas contain 79 peaks that are over 7,500 m high. The highest of these is Mount Everest, which is 8,863 m high. At these altitudes, mountains are always covered in snow and ice, and there is little oxygen to breathe. Although Mount Everest is the tallest mountain when measured from sea level, Mauna Kea in Hawaii is actually the tallest if measured from its base. It reaches 5,818 m below the surface of the Pacific Ocean. From its base to its peak, Mauna Kea is 10,023 m high.

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On top of the world

After many years 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 been conquered. It is now possible to map mountains from the air so that mountaineering routes can be carefully worked out in advance. Also, equipment has improved so that sheer rock faces can be readily climbed. Altitude sickness and avalanches of ice and snow are now the main hazards faced by climbers. 

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