This actually happens far more frequently than anyone thinks, and it's not normally such a big deal. Anyone who's worked for a large telecommunications company knows that this happens dozens of times a year all over the world, but the fact that it occasionally affects the Middle East adds a nice spicy element of conspiracy theory sauce to the mix (especially when Arab governments see an Israeli or American hand behind every action great or small). The most normal cause is boat anchors, but depending on the location, falling rocks from undersea landslides, volcanic activity, etc.