This is true speculation, but makes more sense seeing as blizzard has changed up the lore on Deathwing's arrival recently. Originally Deathwing was stated to rise from the area north of stormwind and the eruption destroyed the park, but in an interview (no source pic, will find) a Blizzard rep stated he now rises from the Maelstrom.
Since the Maelstrom is so far from Stormwind, either deathwing destroyed it while attacking stormwind or...
While this is pure speculation, it would make more sense that Goblins took a chunk out of stormwind in an attempt to kill Deathwing while rising from the Maelstrom/attacking stormwind. The cannon is located in Azshara.