Category Geography

Ice and Snow

Is there such a thing as red snow?

Red snow is found in many parts of the world, when tiny plants grow over the snow and ice. Microscopic algae growing on the surface of snow and ice can give them a red colour. This rare event happens when the weather warms up slightly, and the algae that have been dormant throughout the cold period suddenly start to grow again. 

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What are glaciers?

Glaciers are large masses of ice that form on land and move slowly under their own weight. They are found in cold mountainous places or Polar Regions. Some glaciers are huge continuous sheets of ice, such as those covering Antarctica and Greenland. But most are rivers of ice that move slowly through valleys until they melt and become rivers. Such glaciers are common in the Himalayas, Alps and Rocky Mountains. Because of its enormous weight a glacier scrapes off large amounts of rock and debris, wearing away the valley floor and sides until it carves out a deep ‘U-shaped’ valley. Glaciers formed the deep fjords that line the coast of Norway.

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Ice and Snow

 

Why does snow fall?

Snow forms when water vapour inside a cloud freezes into tiny crystals. The water vapour usually crystallizes around a tiny dust particle called a nucleus, and the snow crystal continues to grow. Crystals of snow clump together to form snowflakes, which fall from the clouds. As many as 100 snow crystals group together to form a 2.5 cm snowflake. Snow crystals are very beautiful in form. They are flat and six-sided, and can grow in the shape of elaborate stars. 

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What is the snow line?

The snow line marks out the area above which a mountain is permanently covered with snow. Because it gets colder as you move higher up, the snow will never thaw on a high mountain. However, the snow line moves higher up during the summer when some of the snow melts. The snow line is close to ground level in cold regions, but it is very high near the Equator where the air is much warmer. 

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Storm and Flood

What is a tsunami?

Tsunamis are tidal waves that are often caused by an undersea earthquake. Usually there is some warning of a tsunami because scientists can detect the seismic waves caused by the earthquake. The tsunami rushes along at up to 970 km/h, building into a wall of water 30 m high as it approaches land. Tsunamis are most common in earthquake zones, particularly around Japan.

Another form of tsunami is called a storm surge, in which giant waves are whipped up by a storm. In 1970 a storm surge and cyclone hit Bangladesh, killing 266,000 people. It returned again in 1985, killing another 10,000 people. 

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How fast can the wind blow?

The fastest wind speed ever recorded was measured on a mountain-top in New Hampshire, USA. It reached 597 km/h. However, the wind inside a tornado probably blows much faster. Wind speed is measured according to the Beaufort scale, which was invented in 1805 by a British admiral. On this scale, the strength of the wind is measured by a series of numbers from 0 to 12. Wind speed 0 means that the air is calm wind speed 9 is a gale strong enough to damage houses. A wind of 12 on the Beaufort scale means a hurricane of over 118 km/h.

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Storm and Flood

How big are hurricanes?

Hurricanes can measure between 320 and 480 km across. They travel at speeds of 16 to 24 km/h, growing larger and stronger as they move. Usually they travel west, and then swing east as they reach cooler regions, before gradually dying out. Repeated hurricanes occur during the storm season, and there may be as many as 15 in a single year. In the USA the National Weather Service tracks hurricanes coming out of the Caribbean and the Gulf of Mexico.lt forecasts the time when they will reach land and the strength of the accompanying wind. 

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The eye of storm

What would you see inside the centre of a hurricane? If you stood in this area, called the eye of the hurricane, you would be in for a surprise. After the violent winds and torrential rain pass over, the wind suddenly drops. A wall of dark churning clouds, hundreds of metres high, surrounds you. There are light breezes and the Sun shines brightly. But you don’t have long to enjoy this peaceful sunny weather, because as the hurricane continues its destructive path it carries the eye with it. You will soon be enveloped in the storm once again. 

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How are hurricanes formed?

Hurricanes are powerful tropical storms that can cause serious damage. They form near the Equator, where warm, moist air rises, drawing in cooler air below. The air moves in a spiral, eventually forming a whirling mass. Rising warm air continues to cool and drop down in the centre of the spiral to repeat the process. The winds inside a hurricane travel at speeds up to 200 km/h. Hurricanes form in the Atlantic Ocean, passing over the West Indies and the southern United States. Similar storms in the Pacific Ocean are called typhoons, whereas in the Indian Ocean they are called cyclones. 

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Storm and Flood

Which world cities are at risk from flooding?

Many of the world’s cities are low lying and threatened by flooding. Bangkok, in Thailand, and Venice, in Italy, are typical old cities built by water because they relied on shipping. Both cities are built on mud and are gradually sinking, increasing the risk of flooding. Sea levels around the world are predicted to rise during this century, with the possibility of devastating flooding in places. Many cities in the Netherlands are below or at sea level. They are always in danger of flooding although elaborate defences help to protect them. The Thames Barrage has been built to prevent high tides flooding the city of London. 

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What are tornadoes?

Tornadoes are violent destructive whirlwinds whose force is concentrated into a much smaller area than that of a hurricane. They are very common in the central United States, where they cause enormous damage. Tornadoes travel across the land at high speed, and the roaring noise they make can be heard 40 km away. A tornado happens when huge masses of clouds moving in different directions meet. The air begins to spin in a spiral, and a funnel of twisting air reaches out towards the ground. The low pressure in the funnel sucks up soil, dust and anything else it touches — even cattle.

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Storm and Flood

What causes floods?

Flooding occurs when water cannot drain away fast enough in the rivers. In areas of non-porous rock, water runs off the land very quickly and streams and rivers soon overflow. Flooding also happens when winter snows thaw in spring. Huge floods cover parts of Siberia every spring, when snow melts while the rivers are still iced up. Low-lying coastal lands are vulnerable to flooding, especially when gales and high tides cause water to flow inland. Low-lying Bangladesh is particularly liable to this kind of flooding. In addition, melting snow in the Himalayan Mountains adds huge amounts of water to Bangladesh’s rivers, increasing the flood risk. 

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Where were the worst floods?

Some of the most terrible floods known were in China along the Hwang-he, or Yellow River. The river burst its banks in 1931, killing more than 3.5 million people. For centuries, dykes have been built to prevent flooding, but these burst when the water flow is too great. Huge dams and sluice gates have been installed to reduce the risk of flooding. 

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