My Science School

 

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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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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