"And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places.  And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bond-man, and every free man, hid themselves in the dens and in the rocks of the mountains;  And said to the mountains and rocks, Fall on us, and hide us from the face  of him that sits on the throne, and from the wrath of the Lamb:  For the great day of his wrath is come; and who shall be able to stand?
  This is a description of the Second Advent, the first account of the end of the tribulation.  The people described in these verses are terrified and are trying to hide from the Lord as he comes down.

The standard interpretation of the book of Revelation is that the judgments in the book are given in chronological order. The problem with that approach, however, is that the Tribulation ends several times in the book (vss. 12-17, 11:14-19, 14:13-20, 19:11-21).  Just as Matthew, Mark, Luke, and John give four accounts of the First Advent, Revelation gives four accounts of the Second Advent.   They are:  1) the Tribulation through the seal judgments (chapter 6),   2)  the Tribulation through the trumpet judgments  (chapters 7-11),    3)  the Tribulation through the activities of the Antichrist (chapters 12-14),  and  4)  the Tribulation through the vial judgments (chapters 15-19). Each account goes through the Tribulation from start to finish, with some parenthetical material inserted (chapters 7, 10, 12, 13).

Eric