Can I leave my position on "short" notice? Specifics: 
-I have completed one year of a tenure-track position at a small school
-I am unhappy in my job. I receive little to no mentorship or institutional support as a junior faculty. My pay and benefits are well below comparable positions in my area. I experience a high degree of stress that is affecting me personally and physically.
-I have been thinking about non-academic jobs for some time and recently received an offer from a consulting recruiter. 

Questions:
-Am I being unethical/insulting by only giving ~1 months notice prior to the semester starting?
-I am technically on a multi-year contract; can I legally break this contract? 
-I anticipate that my leaving will not go over well with the department and I honestly have no idea how to quit (i.e. who do I tell first?, how do I give notice?, etc.), does anyone have advice? 

Thank you!
For the legal consequences, consult your contract. The main consequences in such a situation are likely to be reputational; but if you do not intend to continue in academia, is your reputation among academics really going to affect your career?