Geothermal energy source (6)

I believe the answer is:

geyser

(Other definitions for geyser that I've seen before include "Spring that spouts hot water" , "upsurge" , "Spring spurting hot water upwards" , "It gushes steam and hot water" , "Natural spout of hot water" .)

I've seen this clue in the Newsday.com and the Newsday.

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