A bifurcation or a distributary is the navigational term that means that a river splits in two. Both of these words are used to describe the splitting of the waterway.
a fork
the two rivers are called ganga and jmuna
Two of the most important rivers in India are the Ganges and the Indus rivers
The Mississippi river and something else
The two tribes, Judah and Benjamin, were collectively called Judah or Judea. See also:More about the split
bisect is to split a figure into two congruent parts.
The place where the two rivers join to flow together is called a confluence.
If the split is complete then it's just two continents with names of their own (the current condition of the world). If they're in the process of splinting, the split is called a rift valley (biggest ones today are in Africa).
a confluence
DOAB
a confluence
Pangea
Land between two rivers is called a "river valley" or a "river basin."