1)
What flames does Hashem's voice cleave?
1.
Rashi (from Mechilta Yisro 235): The Dibur of Aseres ha'Dibros came out of His mouth with flames and was carved onto the Luchos. Radak - it says "Es ha'Kolos v'Es ha'Lapidim" (Shemos 20:15).
2.
Radak (11): Just like thunder cleaves lightning flames, so Hashem's anger will burn [the nations] and consume them.
3.
Malbim: The land crumbled, and awesome flames exuded from the depths of the land on the entire Midbar, burning with a storm wind. The verse teaches that Hashem's voice cleaves these flames!
