MemberJanuary 26, 2021 at 4:25 am
I will just paste here some notes I have collected on this topic:
 The Jewish people numbered many thousands (see: The number of the Jews); they owned two-wheeled wagons pulled by pairs of oxen (Numbers 7,3-9), herds of cattle, sheep, and goats. On the move the wagons formed an endless column and the herds were scattered around it for miles since they had to be grazed along the way. To guide and coordinate the movements of such a mass posed a serious problem. Moses solved it in a simple manner, which presumably was common in those times: at the head of the column on the move, a large brazier of burning bitumen was placed on a wagon. A column of dense smoke arose from it which could be seen from a great distance, thus serving as a beacon during the march. At night the glow of the fire in the brazier served the same purpose (Ex. 13,21).
Barbiero, Flavio. “Crossing of the Red Sea.” Altri Occhi Come i Nostri (blog), December 2015. http://www.altriocchi.com/H_ENG/pen4/cronache/red_sea.html.
 Neither the Egyptian army nor the Israelites appear to have been fazed by the sight of a pillar of fire.
Baukal Jr., Charles E. “Pillar of Fire Theories.” Scandinavian Journal of the Old Testament 32, no. 2 (July 3, 2018): 217–35.
 During these marches it is related that the Lord went before the Israelites by day in a pillar of cloud to lead them the way, and by night in a pillar of fire to give them light. With reference to this Linant relates that in modern times the great caravan, which every year sets out from Cairo to Mecca, has a conductor on a camel leading the way. Day and night, whatever the weather is, he remains without any covering naked to the waist. With him march men with large torches, which are kept alight during the night and illuminate the column of smoke above them, so that it appears a pillar of fire. During the day, when the head of the caravan is difficult to see on account of intervening; hills and mounds of sand, the torches are kept burning, so that, instead of the light which served during – the night, a column of smoke rising vertically on calm days might serve as a guide to the straggling caravan from afar, and indicate the time and place of a halt. So was it also arranged in after days when the tabernacle was complete â€” ” the cloud covered it by day, and the appearance of fire by night,” and Israel journeyed or halted according as the cloud was ” taken up ” from the tabernacle or abode upon it.
Brown, Robert Hanbury. The Land of Goshen and the Exodus. London: Edward Stanford, 1899.
 Just as caravan guides in the wilderness are accustomed to carry in front of their caravans certain signals to guide the caravans in the right direction, smoke signals by day and fire by night…
Cassuto, Umberto. A Commentary on the Book of Exodus. Translated by Israel Abrahams. Jerusalem: Magnes, 1967.
 In Exodus 13, it is said that a pillar of cloud by day and a pillar of fire by night accompanied the host. Sir Hanbury Brown, in his book ‘The Land of Goschen and Exodus,’ explains this as being the torches carried by caravans when crossing the desert to mark the route for stragglers–the smoke showing for miles in the clear desert air, and at night the reflection from the torches on the cloud of smoke giving the appearance of a column of fire. This is a very feasible explanation…
Jarvis, Claude S. Yesterday and Today in Sinai. London: W. Blackwood and Sons, 1938.
 Pillar of cloud and fire: the practice of… a brazier… The troops took their cue as to the movement and direction from the smoke and the fire. [ref]
Sarna, Nahum M. Exploring Exodus: The Heritage of Biblical Israel. New York, NY: Schoken, 1986.
[397 n.1] Pillar of cloud and fire. The custom of guiding caravans by means of smoke and light is referred to by many authors.[refs] “Fire was to be the signal by night; smoke by day” [Alexander the Great’s marches] It is not that the pillar of fire and cloud which led the Israelites was not miraculous; but it is that its form and purpose were in the line of Oriental methods.[also Hajj caravans]
Trumbull, H. Clay. Kadesh-Barnea - Its Importance and Probable Site: Including Studies of the Route of the Exodus and the Southern Boundary of the Holy Land. London: Hodder & Stoughton, 1884.
 The text does not suggest that the pillar was supernaturally generated, only that it was the means of supernatural guidance. For this reason, some have suggested that it was the result of a brazier of some sort carried on a pole that  would be used by vanguard scouts. This was a method often used by caravans. On the other hand, the pillar is always portrayed as acting (coming down, moving) rather than being operated (no human is ever said to move it), so the vanguard theory is difficult to support.
Walton, John H., Victor H. Matthews, and Mark W. Chavalas. The IVP Bible Background Commentary: Old Testament. Downers Grove, IL: InterVarsity, 1997.
and a link re bitumen: