Image from David Byrne.com
A reader asks if anyone knows the name of the rocky outcropping just off the tip of Southpoint Park and slightly north of U Thant Island (also known as Belmont Island). It was the subject of an earlier post, Psycho Killer Visits Roosevelt Island – Shoots Cormorants , describing David Byrne’s bike trip to Roosevelt Island when he shot the above photo of Cormorants lounging on the rock.
Took the Roosevelt Island tram instead … , and rode down by the abandoned lunatic asylum. There was no one around. From the tip of the island one has a great view of the UN building and a rocky island filled with cormorants an odd sight for NYC.
I don’t know the name but could the rock islet be remnants from Roosevelt Island’s Delacorte Geyser ? 
Image by Judy Seigel
Concerning the larger U Thant or Belmont Island, it was the site of a daring, others might say stupid, nighttime East River raid during the 2004 Republican national convention. From Wikipedia:
During the 2004 Republican National Convention, NYC artist and film-maker Duke Riley, who has traveled to various “abandoned” islands around the New York City area, rowed a boat with a friend and a bottle of rum [1] to the island under cover of darkness, proclaimed it a sovereign nation and hoisted a 21 foot long pennant depicting two electric eels from the island’s tower. On their return voyage in daylight, they were apprehended by a United States Coast Guard boat, but were not arrested.
You Tube video of Duke Riley – Belmont Island S.M.E.A.C.C. Riley was also responsible for the Red Hook submarine last summer.