'Clean' Power? (image) The Earth Institute at Columbia University Share Print E-Mail Caption Iceland's Hellisheidi geothermal power plant is the world's largest. It is cleaner than those run on fossil fuels, but still emits carbon dioxide by venting volcanic gases. Credit Kevin Krajick/Lamont-Doherty Earth Observatory Usage Restrictions Credit must be given. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.