Section 18
An elective office shall be deemed vacant upon the incumbent's death, incompetence, conviction of a felony, resignation, or removal from the city; or upon the incumbent's 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 within five days after the time for his term of office to commence; and in the case of mayor or councilman, upon his absence from meetings of the council for three consecutive regular meetings of the council without the consent of the council. Vacancies in elective offices of the city shall be filled by appointment by a majority of the members of the council then remaining in office. The appointee's term of office shall begin immediately upon his appointment and qualification therefor and shall continue throughout the unexpired term of his predecessor. During the temporary disability of any officer or during his absence temporarily for any cause, his office may be filled pro tem in the manner provided for filling vacancies in office permanently.