The explosion of the island was quotes as being 50,000 exajoules. Comparing this to the measurement of nuclear explosions converts to 11,950,287 megatons of TNT.
The largest nuclear bomb set off on October 30 1961 was Tsar Bomba which had a blast yield between 50-58 megatons of TNT.
At 09:40 a view of New York from above the East River shows the river and sea level is now way above that of the city, restrained by huge sea walls. Somehow the Manhatten and Brooklyn Bridges have been raised to maintain their positions above the water. In a later episode that view moves more and shows traffic crossing the Manhatten Bridge.