That's what I was wondering about...people don't consider that a retaining wall is actually a dam, the hydrostatic pressure behind the wall can build up quite a bit, especially if the drainage behind the wall is old and it has become plugged up...
It's right after the George Washington Br. heading north, at the beginning of a stretch where there are these massive old stone retaining walls. And I mean massive... I always thought they look like ancient Roman ruins, with aches and aqueducts, etc.
NYC has had a very rainy spring. This, plus the age of the structure, would add to the danger of collapse.