Hugh Nibley
"This, like much else in the account (e.g., that God 'did send down fire and destroy them,' 3 Nephi 9:11), suggests nearby volcanic activity. And indeed, in many cases earthquakes are the preparation for the volcano that follows, as in the Chilean 1960 quake, which triggered the activity of long-dormant volcanoes in the area. Most of the victims of the great catastrophes of Pompeii, St. Pierre (Martinique, 1902), and Mt. Pelee (1906) died of suffocation when earthquake dust, volcanic ash, steam, and hot gasses (mostly sulfureted hydrogen gas) took the place of air. In some areas, the Book of Mormon reports, people were 'overpowered by the vapor of smoke and of darkness,' and so lost their lives (3 Nephi 10:13). Even without volcanic accompaniments, however, major earthquakes kick up a terrible dust and, according to Sieberg, are accompanied by phenomenal vapors and astonishingly thick air. In the Assam earthquake such contamination 'reduced [visibility] to a few feet and made breathing a nightmare.'
"According to 3 Nephi 8:20-21 the 'vapor of darkness' was not only tangible to the survivors, but defeated every attempt to light candles or torches for illumination. At present, intensive studies are being made of the destruction of the Greek island of Thera (today Santorini) in 1400 B.C. This catastrophe, well within historic times, is thought to have been eight times as violent as Krakatoa and is described in terms exactly paralleling the account in 3 Nephi. Among other things it is pointed out that the overpowering thickness of the air must have extinguished all lamps." (Since Cumorah, p. 236)