How do you get the third bomb bag in Twilight Princess?

The second one you get on Lake Hylia,you have to go to the boat place near the Zora's Domain. You have To Blow Up the rocks that are blocking the passage way for the boat by combining the arrow and bomb together,and once you are done the reward is the bomb bag. The third you get by blowing up the volcanic rock in the zoras domain once you have got water bombs and zora armor