Mizbeach and Matzevah

In class we were talking about the difference between a mizbeach and a matzeva. Yaakov builds a matzevah at Bet El after he wakes up from his dream and realizes that G-d was in that place. Why does he build a matzevah and not a mizbeach? A mizbeach is permanent, while a matzevah is temporary. Yaakov is showing us that he can't build anything permanent at that moment, but he has made a commitment to do so in the future. The matzevah is almost a promise or a place holder for what will be there later on. Yaakov will come back and make that place a place for G-d. That is also why he changed the name of the place to Bet-El. He will make sure that soon it will become a place for Hashem.