Text How does an earthquake start?

You can get a pretty good idea of what causes an earthquake from thinking about what happens during an earthquake. During an earthquake, there is a trembling of the ground. It is this trem­bling of the earth which may cause buildings to fall.

So an earthquake is a trembling or vibration of the earth’s surface. What makes it happen? Well, the rock of the earth’s crust may have a “fault”, a kind of break in the crust. The earth blocks shift. Sometimes the sides of the fault move up and down against each other. At other times, the sides of the fault shift lengthwise.

But when one rock mass has rubbed on anoth­er with great force and friction, we have a lot of energy being used. This vast energy that comes from the rubbing is changed to vibration in the rocks. The vibration may travel thousands of miles.

The reason earthquakes take place in certain regions frequently and almost never in other re­gions, is that the faults in the earth’s crust are lo­cated in these regions.

Ex.1 Think and answer.

1 What happens during an earthquake?

2 What causes building to fall?

3 What is an earthquake?

4 What causes the vibration of the surface?

5 What is a fault?

6 What happen with the earth’s blocks?

7 How do the sides of the fault move?

8 What are the reasons of the uneven distribu­tion of the earthquakes on the earth?

Text How does a volcano form?

In February, 1943, in the middle of a cornfield in Mexico, people saw a rare and amazing thing taking place. A volcano was being born! In three months it had formed a cone about 1,000 feet high. Two towns were destroyed and a wide area dam­aged by the falling ash and cinders.

What makes a volcano form? The temperature under the surface of the earth becomes higher and higher the deeper you go down. At a depth of about 20 miles, it is hot enough to melt most rocks.

When rock melts, it expands and needs more space. In certain areas of the world, mountains are being uplifted. The pressure becomes less under these ris­ing mountain ranges, and a reservoir of melted rock (called “magma”) may form under them.

This material rises along cracks formed by the uplift. When the pressure in the reservoir is great than the roof of rock over it, it bursts forth as a volcano.

In the eruption, hot gaseous, liquid, or solid ma­terial is blown out. The material piles up around the opening, and a cone-shaped mound is formed. The “crater” is the depression at the top of the cone where the opening reaches the surface. The cone is the result of a volcano.

The material coming out of a volcano is mainly gaseous, but large quantities of “lava” and solid particles that look like cinders and ash are also thrown out.

Actually, lava is magma that has been thrown up by the volcano. When the magma comes near the surface, the temperature and the pressure drop, and a physical and chemical change takes place that changes the magma to lava.

Ex.1 Think and answer.

1 What could be observed in a cornfield in Mexico in 1943?

2 What happened with a surrounding area?

3 How does the temperature change with the depth?

4 What causes the formation of a reservoir of melted rock under the rising mountain?

5 What is magma?

6 What is the route of the molten material?

7 What are the main products of the eruption?

8 What is called “a cone” of a volcano?

9 What is a crater?

10 What is lava?

Text What is nickel?

Nickel forms many alloys which are used in hundreds of industries in many ways. It is one of the most useful metals known to man. But in early times, when chemists first tried to work with it, it gave them a great deal of trouble. In fact, the word “nickel” is derived from the German word for “imp”!

Nickel is found in meteorites, and it is sometimes found in the free state in small quantities. But the greatest supply of nickel is obtained from certain ores, especially one called pyrrhotite, which is a mineral containing iron, copper, and nickel. Canada is the greatest of all nickel-producing countries.

The ore containing nickel is usually heated in a blast furnace to obtain a rich mixture. This is then reduced to nickel by mixing it with coke and heating it in a blast furnace.

Nickel is silvery, lustrous, hard, and malleable, which means it can be easily worked and shaped. And nickel is one of the most magnetic materials known, unless heated.

We seldom see pure nickel except when it is used as a coating on other metals. This is then called nickel-plate. It protects other metals from rust or tarnish, and gives them a better wearing surface.

Most of nickel produced is used in alloys, or in a mixture with other metals. For instance, when al­loyed with copper, it is used in coins. Our own five-cent piece is called a nickel for that reason. When it is alloyed with three parts of copper and one of zinc, nickel forms a bright silvery metal known as German silver or nickel silver.

This is used for mak­ing tableware and as a base for silverplated ware. But these uses of nickel are relatively minor. Most nickel goes into the making of nickel steel, an alloy which can withstand repeated strains. It is used in structural work, bridges, railroad rails at curves, rivets, locomotive boilers, automobile gears and axles.