Get Destruction to 100, talk to Faralda in the College of Winterhold. She'll give you a book with riddles in it, which will point you to 3 locations. At those locations, put the book on the pedestal, hit it with its respective spell (there's a pedestal for fire, ice and lightning). After all 3 pedestals, you will learn Fire Storm and Faralda back at the College will sell you Blizzard and Thunder Storm.