Destruction of the snakes

Several scriptures found in the book of Ether help us to further define the Book of Mormon term "narrow neck of land."

You will recall that about 1300 BC, during the reign of King Heth (the 9th Jaredite king), the Lord cursed the people with a grievous famine.  It was so severe that even the king died.  The famine was accompanied by an infestation of poisonous snakes which migrated en mass southward afflicting both man and beast.  The surviving animals fled before the snakes, passing through the narrow neck of land, into the land southward (Alma 22:41), which later came to be known as the land of Zarahemla.  About 400 years later the plague of snakes was successfully destroyed giving the Jaredites access to the land southward which they hadn't had for many years.  The first series of scriptures that speak of this is found in Ether 9:29-34. 

But the people believed not the words of the prophets, but they cast them out; and some of them they cast into pits and left them to perish. And it came to pass that they did all these things according to the commandment of the king, Heth.  And it came to pass that there began to be a great dearth upon the land, and the inhabitants began to be destroyed exceedingly fast because of the dearth, for there was no rain upon the face of the earth.  And there came forth poisonous serpents also upon the face of the land, and did poison many people. And it came to pass that their flocks began to flee before the poisonous serpents, towards the land southward, which was called by the Nephites Zarahemla.  And it came to pass that there were many of them which did perish by the way; nevertheless, there were some which fled into the land southward.  And it came to pass that the Lord did cause the serpents that they should pursue them no more, but that they should hedge up the way that the people could not pass, that whoso should attempt to pass might fall by the poisonous serpents.  And it came to pass that the people did follow the course of the beasts, and did devour the carcasses of them which fell by the way, until they had devoured them all. Now when the people saw that they must perish they began to repent of their iniquities and cry unto the Lord.

About 400 years later, during the reign of King Lib (the 13th Jaredite king), Lib managed to

destroy the plague of serpents to the extent that men could travel thru the narrow neck 

without being bitten.  We are not told how this was accomplished, but my opinion is that they used repeated burning of the land which would have effectively annihilated the snakes over several years.  This repeated burning may also explain why there were few trees in the land northward when the Nephites later began to inhabit the land (Hel. 3:6-7).  

Sometime previous king Lib had built a large city near the narrow neck (presumably to the north), near a geographical feature called "the place where the sea divides the land."  These references thus relate the land northward, the narrow neck of land, the city of Lib, and the land southward (or Zarahemla) spatially.  These references are found in Ether 10:19-21.  

And it came to pass that Lib also did that which was good in the sight of the Lord. And in the days of Lib the poisonous serpents were destroyed. Wherefore they did go into the land southward, to hunt food for the people of the land, for the land was covered with animals of the forest. And Lib also himself became a great hunter.  And they built a great city by the narrow neck of land, by the place where the sea divides the land.  And they did preserve the land southward for a wilderness, to get game. And the whole face of the land northward was covered with inhabitants.

See also https://moriancumr2.blogspot.com/2014/01/seeking-city-of-lib.html