Using the word 'aggressive' to describe the mother moose, in this context, is completely inappropriate.  A better word to use would have been 'defensive,' and with good reason.  She did what she was supposed to do.  If she'd been left alone, this could have been avoided.
     Humans set up this situation by their sheer stupidity.
     I say that because, due to the proximity, this moose family group was almost certainly the same mother-and-twins that were near Ft. Richardson exit on the Glenn Highway for several days--immediately post-birth, as a matter of fact.  
     Within minutes of the 'arrival,' a continuous string of obnoxious, unfeeling, uncaring, unthinking, boorish Looky-Lous began a parade of vehicles stopping only yards away from the group, to stare, snap photos, and share on social media, making Mom more skittish and more likely to react badly later on.
     Every thoughtless wretch who stopped to stare shares the blame for this.
     Congratulations.