Among proponents of the theory that Mount Sinai must be in Saudi Arabia, some have suggested that the Hala-‘l Badr volcanic mountain is the best candidate. This candidacy is largely based on an assumption that the phenomenon described in the Exodus story must be the result of volcanic activity in the immediate vicinity of Moses and the Israelites.
Supporters of this theory believe that Mount Sinai must be in ancient Midian and, more specifically, northwestern Saudi Arabia and southern Jordan. The Hala-‘l Badr candidacy is based on the assumption that the “devouring fire” described in the Exodus story is a description of a volcanic eruption, thus requiring Mount Sinai to be a volcano. They also suggest that the Israelites equated Yahweh with the god of the volcano, and so their version of God is a slightly evolved version of ancient, polytheistic religious beliefs.
The theory was first proposed by a German scholar of the Old Testament named Hermann Gunkel who lived from 1862 to 1932. He first advocated for Hala-‘l Badr as Mount Sinai in his book, Genesis, published in 1901.
In his book Genesis, Gunkel wrote:
The characteristic Israelite narratives of Yahweh’s appearance in the burning thorn bush (Exod. 3:2), in the burning and smoking Sinai (Exod. 19:9, 20:18; Deut. 4:11), and especially in the pillars of smoke and fire (Exod. 13:21)…can be explained originally from the fact that, in Israel’s earliest belief, Yahweh was the god of the Sinai volcano. 
The biggest difficulty with this candidate and the overall theory that Mount Sinai must be a volcano it requires the Exodus story to be exaggerated, inaccurate and/or to be missing important details. This theory is therefore discarded by those looking for a literal match with the criteria so that it does not contradict the text.
The destructiveness of a volcanic eruption would have killed Moses if he was on the mountain when it occurred, as well as likely destroyed the Israelite encampment in front of the mountain. The Exodus story does not describe the phenomenon as causing massive casualties, forcing the Israelites to flee away or destroying the area where they settled. It is also probable that the brook that is described as coming down from Mount Sinai would have been contaminated and no longer usable for the population.
The most well-known advocate of the candidacy of Hala-‘l Badr Saudi Arabia is Hermann Gunkel.
Other authors who believe that Mount Sinai must be a volcano in northwestern Saudi Arabia include Charles Beke, Sigmund Freud, Immanuel Velikovsky, Colin Humphreys, Eduard Meyer, and Martin Noth.
 Hermann Gunkel, Genesis (trans. M.E. Biddle; Macon, GA: Mercer University Press, 1997), 181.