The editors of the 1852 LDS edition realized that (in the biblical language of Early Modern English) verbs ending in -(e)th (such as ascendeth) should take third person singular subjects, so flames was edited to flame. But in the original Book of Mormon text, the -(e)th ending is frequently used with plural subjects, so that an alternative editorial decision would have been to keep the plural flames and change the verb to ascend (and also change the following verb to have ).
In two other instances, the earliest text also had flames and once more the associated verb form was ascendeth, so the plural flames was changed to flame in favor of the singular:
Again both of these changes in number were implemented by the editors of the 1852 LDS edition. These two examples could have also been edited to read “flames ascend”. Of course, the critical text will restore the original “flames ascendeth” in all three cases. For further discussion, see infl al endings in volume 3.
The plural use of flames in this context of the “lake of fire and brimstone” is in fact expected, as in the following two examples where the verb is the plural are:
Summary: Restore the original “flames ascendeth” in 2 Nephi 9:16, Mosiah 2:38, and Alma 12:17; two other passages use the plural flames, not the singular flame, to refer to the lake of fire and brimstone (“whose flames are unquenchable”, in Jacob 6:10 and Mosiah 3:27).