Tonnes, Kilotonnes and Megatonnes

Distances are typically measured in metres (do you know what the SI symbol for a metre is?). Times are usually measured in seconds (do you know what the SI symbol for a second is?).

When you measure something, like the length of a piece of rope in metres then you need to write down two pieces of information so that other people know how long the rope is. The first piece of information is the number of metres long the rope is. The second piece of information is the unit you measured the rope in. If the rope is 1.59 metres long then you write

1.59 m

It's the same thing when you want to measure the size of an explosion. You give the number and then you give the units you measured the number in. In this case the unit you measure explosions in is the

tonne

A `tonne' is equivalent to the explosion generated by one tonne of TNT (which is short for chemical name trinitrotoluene). So a kilotonne is equivalent to the explosion generated by 1,000 tonnes of TNT.

1,000,000

You really need to use megatonnes and kilotonnes when you start talking about huge explosions like atomic bombs. On 30th October 1961 the Soviet Union exploded a 50 megatonne thermonuclear bomb over Novaya Zemlya island in northern Russia above the Arctic Circle at an altitude of 4,000 meters. The atmospheric disturbance generated by the explosion orbited the earth three times. The flash of light was so bright that it was visible at a distance of 1,000 kilometers, despite cloudy skies. A gigantic, swirling mushroom cloud rose as high as 64 kilometers.

In fact, the explosive of this single device was 10 times the total power of all explosives used during World War II, including the atomic bombs dropped on Japanese cities by the United States.

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