The island in the alt timeline

What happened to the island in the alt timeline is a big question for me, we see it at the bottom of the ocean, but we also know that Ben and his dad still went there so it was fine say at least 30 years ago.
Any ideas on what caused it to sink? We did see a massive tsunami like wave land the black rock, and of course maybe jughead played a part.

Maybe in the alt timeline someone else caused there very own incident.

But more importantly, what were the consequences for Jacob & MIB in the sunken island alt timeline?