The Holy Bible, Revelation 8:5-6

5 And the angel took the censer, and filled it with fire of the altar, and cast it into the earth: and there were voices, and thunderings, and lightnings, and an earthquake.

6 And the seven angels which had the seven trumpets prepared themselves to sound.

The Doctrine and Covenants, Section 43:25

25 How oft have I called upon you by the mouth of my servants, and by the ministering of angels, and by mine own voice, and by the voice of thunderings, and by the voice of lightnings, and by the voice of tempests, and by the voice of earthquakes, and great hailstorms, and by the voice of famines and pestilences of every kind, and by the great sound of a trump, and by the voice of judgment, and by the voice of mercy all the day long, and by the voice of glory and honor and the riches of eternal life, and would have saved you with an everlasting salvation, but ye would not!

The Doctrine and Covenants, Section 49:23

23 Wherefore, be not deceived, but continue in steadfastness, looking forth for the heavens to be shaken, and the earth to tremble and to reel to and fro as a drunken man, and for the valleys to be exalted, and for the mountains to be made low, and for the rough places to become smooth–and all this when the angel shall sound his trumpet.

The Doctrine and Covenants, Section 77:12

12 Q. What are we to understand by the sounding of the trumpets, mentioned in the 8th chapter of Revelation? A. We are to understand that as God made the world in six days, and on the seventh day he finished his work, and sanctified it, and also formed man out of the dust of the earth, even so, in the beginning of the seventh thousand years will the Lord God sanctify the earth, and complete the salvation of man, and judge all things, and shall redeem all things, except that which he hath not put into his power, when he shall have sealed all things, unto the end of all things; and the sounding of the trumpets of the seven angels are the preparing and finishing of his work, in the beginning of the seventh thousand years–the preparing of the way before the time of his coming.

The Doctrine and Covenants, Section 88:108-110

108 And then shall the first angel again sound his trump in the ears of all living, and reveal the secret acts of men, and the mighty works of God in the first thousand years.

109 And then shall the second angel sound his trump, and reveal the secret acts of men, and the thoughts and intents of their hearts, and the mighty works of God in the second thousand years–

110 And so on, until the seventh angel shall sound his trump; and he shall stand forth upon the land and upon the sea, and swear in the name of him who sitteth upon the throne, that there shall be time no longer; and Satan shall be bound, that old serpent, who is called the devil, and shall not be loosed for the space of a thousand years.

The Doctrine and Covenants, Section 88:92-95

92 And angels shall fly through the midst of heaven, crying with a loud voice, sounding the trump of God, saying: Prepare ye, prepare ye, O inhabitants of the earth; for the judgment of our God is come. Behold, and lo, the Bridegroom cometh; go ye out to meet him.

93 And immediately there shall appear a great sign in heaven, and all people shall see it together.

94 And another angel shall sound his trump, saying: That great church, the mother of abominations… is ready to be burned. And he shall sound his trump both long and loud, and all nations shall hear it.

95 And there shall be silence in heaven for the space of half an hour; and immediately after shall the curtain of heaven be unfolded, as a scroll is unfolded after it is rolled up, and the face of the Lord shall be unveiled;

Journal of Discourses, Orson Pratt 15:41

“… And the sounding of the seven trumps is the preparing and finishing of his work in the morning of the seventh thousand years.” This gives a clue to the time when the seven angels will sound. They will not sound their trumpets in the evening of the sixth thousand years, but when the six thousand years shall have passed away from the creation, and the morning of the seventh has commenced, then these great events will happen. Jesus does not come immediately at the commencement of the seventh thousand years, but as there was a work in the beginning which he performed on the seventh day, such as planting the garden and placing men therein, so there will be a certain work to be performed in the beginning of the seventh thousand years, namely, the resurrection and redemption of man, including the heathen nations and those people in prison who have died without the law and have been punished for their sins. When the Lord has caused these seven angels to sound their trumps, he will bring about all these purposes which he has ordained, and which must be accomplished in that morning. Before Jesus appears in the clouds of heaven they are to sound to prepare the way of the Lord before his coming.

Journal of Discourses, Orson Pratt 16:43

[T]he sounding of the trumpets does not take place, as many have supposed, in rapid succession, but certain events have to be accomplished between their respective soundings.

Journal of Discourses, Orson Pratt 16:45

We read there that when the first angel among the seven shall sound his trump, all nations and kindreds and tongues of the earth shall hear it. Will it be so much louder than any sound we now hear, that it will go to all the nations and tongues of the earth and all men hear it? “Every ear,” the revelation says, shall hear the sound of that trump; it will be something that all the kindreds, peoples, tongues and nations upon the face of the whole earth will be able to perceive and understand. Now, there must be some medium through which this sound is transferred, different from our atmosphere; or, in other words, the Lord, by his miraculous power, will cause this sound to proceed forth through the atmosphere in a different manner from what it now proceeds, for if it took the sound of that trump five seconds to go a mile, it would require a long time for it to travel eight, ten or fifteen thousand miles, so as to reach the ears of the different nations of the earth. Does not this prove then, that God will, at that time, either effect the ear of man or act upon some materials in connection with our globe, so that sound will be more rapidly conveyed than it is at the present time?

Journal of Discourses, Orson Pratt 18:28

These plagues named in John’s revelations, will take place literally–”The Lord God will curse the waters of the great deep, and they shall be turned into blood.” “The sea shall become as the blood of a dead man, and every living thing in the sea shall be destroyed.” And the time will come, when the seven angels having the seven last trumps will sound their trumps literally, and the sound thereof will be heard among the nations, just preparatory to the coming of the Son of man; and all the judgments foretold by John, which are to succeed the sound of each of the seven trumpets, will be fulfilled literally upon the earth in their times and seasons.