Well That's Interesting . . . .

 Q. 338   Can a General Council Depose the Pope?

Strictly speaking, such a council could depose a Pope only in the case the Pope became a heretic, not however if he became immoral.  Where there are several pretenders, as happened during the Western Schism, the council passes on the claims of each, declares a certain one to be the rightful Pope, according to the proofs, and if this man approves the decrees he becomes the lawful  pontiff.  Even then he may abdicate.

-from "Setting it Right" , by the Rev. Dr. Charles F. McGinnis, Ph.D., S.T.L., formerly Professor of philosophy in St. Thomas College and Professor of Apologetics in College of St. Catherine, St. Paul, Minn., Author of "The Communion of Saints", etc., etc.