I'm one of the admitted Columbia EES students. A PI I didn't list on my application contacted me via email in late January and we had a Skype interview.
It sounds like they might admit by discipline, since my prospective PI said she was hoping to get many admitted SGT (seismo geophysics tectonics) people to come on the same day, and had already had contact with a few. Don't know why notification time matters, but I received an "unofficial" admit w/funding details at 11:30ish AM and then an "official" admit the next day around 1pm. My early notification might also have to do with funding, though (Dean's Fellowship), so who knows.
alpha1002 got a reaction from wandering95 in 2018 Applicant Profiles and Admissions Results