Hmm, a solution...what is the solution anyway? I mean really, if the solution ain't firing Alpha halo, then what was it? It can't be killing the Gravemind either since he is not supposed to know where the portal leads to. Was it really a flood trap set up by the Gravemind because if it is, Cortana should have already been in a state of rampancy. While we're at it...


What he said.

Damn these plot holes are annoying.
-Zekilk

Kinda confusing what you're pointing at in the second quote, but as for the infected Covenant Cruiser, it was so easily stopped by glassing half a continent, if the Elites hadn't moved faster, all of Africa would have become flood controlled.

Why would the Gravemind allow its enemies to rush to a wealth of forerunner technology that might possibly destroy its kind? Or severely cripple it? Even in a tactical decision that sounds kind of stupid and the Gravemind is not really known for making split second decisions, everything it does is because of cold, calculated thoughts.
Moreover, as far as we know (according to canon thus far) the Flood never reached the Ark and thus, have no collective knowledge of what it does or what its capable of.