Islands of Four Mountains from Above . ... Credit Copyright: Earth Observatory , NASA , Terra satellite, ASTER ; Processing by: Jesse Allen Robert Simmon Explanation: Our Earth is covered by volcanoes. Volcanoes are breaks in the Earth's cool surface where hot liquid rock from the interior comes out -- sometimes suddenly . ... Cleveland , an active volcano currently being watched to see if it emits an ash cloud that could affect air travel over parts of North America. ...