An office shall be deemed vacant upon the incumbent's death, incompetence, conviction of a felony, resignation, or absence from the city for 30 days without the consent of the council in the case of mayor or councilperson; upon the incumbents ceasing to possess the qualifications necessary for his office; or upon the failure of the person elected or appointed to an office to qualify therefor on or before the day his term of office commences; and in the case of mayor or councilperson, upon his absence from meetings of the council for 60 days without the consent of the Council.