In Alma 12:14,16-17, Alma explains to the wicked people of Ammonihah
14 For our words will condemn us, yea, all our works will condemn us; we shall not be found spotless; and our thoughts will also condemn us; and in this awful state we shall not dare to look up to our God; and we would fain be glad if we could command the rocks and the mountains to fall upon us to hide us from his presence...
16 And now behold, I say unto you then cometh a death, even a second death, which is a spiritual death; then is a time that whosoever dieth in his sins, as to a temporal death, shall also die a spiritual death; yea, he shall die as to things pertaining unto righteousness.
17 Then is the time when their torments shall be as a lake of fire and brimstone
We know the story. A horrible scene unfolds in which the men who believe the words of Alma and Amulek are thrown out of the city and their women and children are burned in a great fire. In 14:14
Now it came to pass that when the bodies of those who had been cast into the fire were consumed, and also the records which were cast in with them, the chief judge of the land came and stood before Alma and Amulek, as they were bound; and he smote them with his hand upon their cheeks, and said unto them: After what ye have seen, will ye preach again unto this people, that they shall be cast into a lake of fire and brimstone?
The chief judge sarcastically refers to their preaching in Alma 12:17, where a lake of fire and brimstone was mentioned. The chief judge is trying to demonstrate who really has the power to cast people in the fire. Verse 15
Behold, ye see that ye had not power to save those who had been cast into the fire; neither has God saved them because they were of thy faith. And the judge smote them again upon their cheeks, and asked: What say ye for yourselves?
...and verse 19
Know ye not that I have power to deliver you up unto the flames?
OK, he made his point. But the wicked chief judge missed an important point of Alma's message in chapter 12: The lake of fire and brimstone has nothing to do with the first death or the physical death. It is what happens to the wicked as a second death, a death over which the chief judge has no power. Those who the chief judge had sentenced to a first death in the flames would not suffer a second death. Alma said about those in 14:11:
the Lord receiveth them up unto himself, in glory
Do you recall what Alma said in 12:14 about those whose thoughts, words and actions condemn them? In an ironic twist, after Alma and Amulek have suffered long enough, the following happens to the wicked city leaders:
And it came to pass that so great was their fear that they fell to the earth, and did not obtain the outer door of the prison; and the earth shook mightily, and the walls of the prison were rent in twain, so that they fell to the earth; and the chief judge, and the lawyers, and priests, and teachers, who smote upon Alma and Amulek, were slain by the fall thereof.
The prison walls (made of rock?) fell over them causing them to suffer the first death. Their fate would now be to wish the rocks could fall over them again but instead having to suffer the second death in a lake of fire and brimstone.