Jamieson, Fausset and Brown on Zechariah 14:4

4. The object of the cleaving of the mount in two by a fissure or valley (a prolongation of the valley of Jehoshaphat, and extending from Jerusalem on the west towards Jordan, eastward) is to open a way of escape to the besieged (compare Joe 3:12, 14). Half the divided mount is thereby forced northward, half southward; the valley running between. The place of His departure at His ascension shall be the place of His return: and the "manner" of His return also shall be similar (Ac 1:11). He shall probably "come from the east" (Mt 24:27). He so made His triumphal entry into the city from the Mount of Olives from the east (Mt 21:1-10). This was the scene of His agony: so it shall be the scene of His glory. Compare Eze 11:23, with Eze 43:2, "from the way of the east."