Unit 5 The power of nature教案
sample expressions：
what happened in the pictures above？do you know any other natural disasters？please work with your partners and make a list of natural disasters(such as earthquake，snowstorm，flood，drought).have you ever seen a volcano?
(some new words：lava erupt/eruption crater active/dormant/extinct volcanoes...)
2.warming up by reading the passage below.
some knowledge about volcanoes
there are thousands of volcanoes all over the world.what makes volcanoes？what happens?
the inside of the earth is very hot.because it is very，very hot，the rock has melted like ice.it has become liquid，like water.it is always boiling，like water in a kettle.if you have seen a kettle boiling，you know that the steam and boiling water try to get out.the very hot melted rock inside t he earth also tries to get out.usually it cannot because the outside of the earth is too thick and strong.
but in some places the outside of the earth is thin and weak.sometimes a crack(a small opening)appears.the hot melted rock，which we call “l(fā)ava”，pushes up through the crack and bursts through.steam and gas shoot up into the air and the hot melted lava pours out.big pieces of rock may be thrown high into the air.
after a while the volcano becomes quiet again.the melted lava becomes hard.later the same thing happens again and again.each time more hot lava pours out on top of the cold lava and then becomes hard.in this way a kind of mountain is built up，with a hole down the middle.perhaps the volcano will then be quiet and no more lava will burst out.perhaps it will start again hundreds of years later.
vesuvius is the name of a very famous volcano in italy.it first came to life many，many years ago.it was quiet for hundreds of years.then in the year 79 it suddenly burst.a great cloud of smoke shot up into the sky with great burning rocks，which fell all around.hot lava poured down its sides.about 3000 people were killed.
step 2 pre－reading
1.can you imagine climbing into a live volcano in order to measure the temperature of the boiling rock inside？now，read the following passage please.
why does tazieff risk his life like this?
haroun tazieff，the polish scientist，has spent his lifetime studying active volcanoes and deep caves in all parts of the world.in 1948，he went to lake kivu in the congo to observe a new volcano which he later named kituro.tazieff was able to set up his camp very closed to the volcanoes while it was erupting violently.though he managed to take a number of b rilliant photographs，he could not stay near the volcanoes for very long.he noticed that a river of liquid rock was coming towards him.it threatened to surround him completely.but tazieff managed to escape just in time，he waited until t he volcanoes became quiet and he was able to return two days later.this time，he managed to climb into the mouth of kituro so that he could take photographs and measure temperatures.tazieff has often risked his life in this way.he has been able to tell us more about act ive volcanoes than any man alive.