In winter, the Hudson River is not only dynamic in its tides and currents, but also in the tremendous power of its ice.  Standing on the river's western shore in Cornwall, I was astonished at the roar it made as it floated on the south flowing current, crashing into enormous masses of previously shattered ice.  I imagined it to be a model of what tectonic plates must be like as they fracture the earth's crust in their inexorable movement.  In several months, the ice will be gone, but the rocks it has rearranged, the piers and landings it has damaged, and the newly carved scars in the banks of the river will remain.