During the “Great Tribulation Period” and mainly during the “Wrath of God” time period, most of the population of the world will be destroyed by Volcanic Fire.
88. Earthquake, Fire and Brimstone.88
371. Volcanic Eruptions.371
378. Volcanic Ash Cloud. Part 1.378
379. Volcanic Ash Cloud. Part 2.379
380. Volcanic Ash Cloud. Part 3.380
383. Volcanic Ash Cloud. Part 4.383
384. Volcanic Ash Cloud. Part 5.384
Here are a few videos that show the meaning of the term:
Fire and Brimstone:
Psalm 11:  Upon the wicked he shall rain snares, fire and brimstone, and an horrible tempest: this shall be the portion of their cup.
Ezekiel 38:  And I will plead against him with pestilence and with blood; and I will rain upon him, and upon his bands, and upon the many people that are with him, an overflowing rain, and great hailstones, fire, and brimstone.
Luke 17:  But the same day that Lot went out of Sodom it rained fire and brimstone from heaven, and destroyed them all.
Revelation 14:  The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:
Revelation 20:  And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
Revelation 21:  But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.