The Then and Now would be quite amazing, actually. The Yanks stopped clearing out the fallen debris some time ago, as it would slow down the erosion.
There's a big dolomite disk in the Great Lakes, minus Lake Ontario. This disk ends around Niagara, which is why the escarpment is so defined. Underneath is limestone, which is much softer. Moving water erodes it and leaves the dolomite sticking out, until it breaks off like peanut brittle. The debris breaks the water's fall, and reduces its impact on the limestone. There's a big ramp at the bottom of the American Falls now, whereas they clean them out on Horseshoe Falls.