Прочитайте текст. Тезисно сформулируйте сходства и различия между ледниками и потоками воды

Glaciers are defined and often popularly referred to as streams of ice. In shape and in the fact that they run downhill, they are like streams of water, but there most similarity ends. Glaciers are aggregates of ice which move slowly. The effects of glaciations, like those of all other surface processes, are erosion of the highlands and filling of the low places. There is therefore both abrasion and deposition.

There are very significant differences between the behavior and the properties of glaciers and streams. A glacier is an accumulation of crystalline solid ice. It is essentially a rigid body. A river is a stream of liquid which has no rigidity, which has none of the properties of a solid. A glacier can support upon and within itself masses of rock which are of greater specific gravity than ice; streams cannot carry in suspension large masses of materials of a higher specific gravity than water. Water can never run uphill; glaciers can move uphill very commonly. Water which meets loose materials flows over or around it, while ice can push this material in front of it. Water will run over a cliff in a continuous stream; ice in such a circumstance breaks into separate pieces which fall as individual blocks, broken from a solid mass. Water which flows slowly over an uneven surface conforms itself to its irregular bed; a glacier going over irregularities cannot bend and therefore cracks. These differences directly result from the fact that a river is liquid and a glacier is a rigid, crystalline solid.

Ex. 24.

Прочитайте текст «What is quicksand» и ответьте на следующие вопросы:

1. What is quicksand?
2. What are the main properties of quicksand?
3. What is the difference between sand and quicksand?
4. Why does quicksand contain water?
5. How does the form of grains of quicksand differ from that of sand?
6. Why is quicksand unable to support solid objects?
7. Does quicksand always contain sand?
8. Is quicksand dangerous for people?

What is quicksand?

What is quicksand? It is a light, loose sand which is mixed with water. It does not look different from sands which might be right next to it. But there is a difference: quicksand will not support heavy ob­jects.

Quicksand usually occurs near the mouths of large rivers and on flat shores where there is a lay­er of stiff clay under it. Water is collecting the sand because the underlying clay keeps the water from draining away. This water may come from many different places, such as river currents or pools.

The grains of quicksand are different from or­dinary grains of sand because they are round in­stead of being angular or sharp. The water gets between the grains and separates and lifts them, so that they tend to flow over one another. This makes them unable to support solid objects.

Some quicksand is not even made of sand. It can be any kind of loose soil, a mixture of sand and mud, or kind of pebbly mud.

People who step into quicksand do not sink out of sight. Since it contains so much liquid, it will enable them to float. And since quicksand is heavier than water, people can float higher in it than they do in water.

The important thing is to move slowly in quick­sand. This is to give it time to flow around the body. Once it does this, it will act like water in which you are swimming.

Unit IX. Test Section.