This would be the alternate problem. If there was a crusted type by the time bodies hit the lava then it would not have the appearance of the lake described in the scriptures. There is one other point about this that the spirit has brought to my mind last night... A normal earthly fire cannot kill the soul so, based on this I would say that the only fire that could perform both destructions is the very presence of God himself.
I humbly offer these scriptures;
Nahum 1:6 Who can stand before His indignation? Who can endure the burning of His anger? His wrath is poured out like fire And the rocks are broken up by Him.
Deuteronomy 4:24 "For the LORD your God is a consuming fire, a jealous God.
Jeremiah 4:4 "Circumcise yourselves to the LORD And remove the foreskins of your heart, Men of Judah and inhabitants of Jerusalem, Or else My wrath will go forth like fire And burn with none to quench it, Because of the evil of your deeds."
Malachi 3:2 "But who can endure the day of His coming? And who can stand when He appears? For He is like a refiner's fire and like fullers' soap.
There is one small point that appears to be unreconciled though since i'm fairly certain that sulfur is not part of the fire spoken of in the above verses and it is in this verse;
Revelation 21:8 But as for the cowardly, the faithless, the detestable, as for murderers, the sexually immoral, sorcerers, idolaters, and all liars, their portion will be in the lake that burns with fire and sulfur, which is the second death.”
A normal earthly fire cannot kill the soul? Are you are that animals too also have souls, and their souls are destroyed when they die? The soul is kept or destroyed by the will of God, nothing to do with being near or far from his presence, and he can choose how he wants to destroy the soul of a man.