Charles Allen and his brother Bill Allen have learned a lot about geothermal energy. Here are some questions that students have sent to them. Charles and Bill have lots of colleagues in the geothermal industry. If they don't know the answer to your question, they'll forward it to an expert for an answer!

Dear Charles,
You're always talking about magma. So what is it, where does it come from, why is it hot, and where can I go to see some?  
Sincerely,
Amanda S.

Dear Amanda,
Wow! Well, first, magma is melted rock. It's made within the mantle--the layer of rock that lies just beneath the earth's crust. That means it comes from 60 to 200 miles down. The rock keeps melting because it's so hot down there.

And it stays hot! Sounds unbelievable but it’s true. The heat inside the earth is always being regenerated by breakdown of radioactive elements. So the rock stays melted. The Earth's heat will always be around. That's why geothermal energy is a renewable energy source.

You have seen hot magma if you have seen a volcano erupt, maybe on TV. Lava is really the magma which is breaking right up through the earth's crust.
Charles  

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Dear Bill,
Will we ever run out of geothermal energy?  
Sincerely,
Nikki N.

Dear Nikki,
No. Future generations will always have geothermal energy. Hydrothermal reservoirs contain both water (hydro) and heat (thermal). The heat is always being generated deep in the earth. The water is replenished by rainfall and by returning the used water back into the reservoir.
Bill

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Dear Charles,
If there is geothermal heat in the earth, why don't my feet get hot?  
Yours Truly,
Jordan M.

Dear Jordan,
They would if you put them in a hot spring, but most places it gets hot slowly as you get deeper. Geothermal energy is everywhere but mostly at a safe depth.
Charles

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Dear Bill,
If geothermal is so great, why don't we use it to make all our electricity?  
Louis A.

Dear Louis,
We would if we could. Making electricity needs high temperature geothermal near the surface to be economical with present day technology. So far, we only find high temperature geothermal in a few places. Some other countries with fewer people and more volcanoes could get all their electricity from geothermal resources.
Bill

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