According to Hugh Nibley, the description of how people were driven out of a land by a plague of serpents that then "hedge up the way that the people could not pass" (Ether 9:31-35) may put a strain on some people's scientific credulity. Nevertheless it can be believed: "Pampa the Great, we are told, could not get his army into Hyrcania because the way was barred by snakes along the Araxes, a stream that still swarms with the creatures. . . Shah Sadrudin set his heart on the building of a capital which should surpass all other cities in splendor; yet the project had to be abandoned after enormous expense when during a period of drought the place so swarmed with serpents that no one could live in it." It is interesting in this connection that the plague of serpents in Ether is described as following upon a period of extreme drought (Ether 9:30). [Hugh Nibley, The World of the Jaredites, p. 221]
Geographical [Theory Map]: Ether 10:1 - 10:16 People Begin to Spread Over All the Land (Chronology)
The Serpents Did Hedge Up the Way
If the serpents "hedged up the way" (Ether 9:33) so that the people couldn't follow the flocks into the land southward, then this seems to imply that there was a "limited" passage into the land of Zarahemla. This migration of animals "into the land southward" seems to be talked about by Mormon in Alma 22:21 when he says, "the land on the southward (of the land northward [Desolation]) was called Bountiful, it being the wilderness which is filled with all manner of wild animals of every kind, a part of which had come from the land northward for food." Mormon also goes on to say in Alma 22:32 that there was "a small neck of land between the land northward and the land southward." Perhaps this "small neck of land" was what allowed the serpents to "hedge up the way." [See the commentary on Alma 22:31-32; Ether 10:19; 10:21]
Glenn Scott notes that the river which flows across the Isthmus of Tehuantepec (a proposed area for the small neck of land and thus a proposed area where the serpents might have "hedged up the way" -- Ether 9:33) is named the Coatzacoalcos, which in the Nahuatl language means, "the place of serpents." (Robert Fishburn 1968, "Place of Serpents," FRAA Newsletter 2:4) [Glenn A. Scott, Voices from the Dust: New Light on an Ancient American Record, p. 51]