The new photos seem to support my contention they split the switch and the speed was closer to 20 than 10 mph. If the engineer had plugged it well before the switch, I would have expected them to have stopped short or on the switch. The jack-knifed cars show that the front stopped yet the mass of the 15 car train continued to push unrestrained. Had an emergency brake application already been in effect prior to the derailment, I would not have expected as severe as a jack-knife.
10 mph is about 15 feet per second, and 20 mph would be 30 feet per second. Assuming the engineer plugged it within a few seconds of derailing, there was still a lot of momentum and mass without enough time for the brakes to take effect, with the derailment itself providing a good portion of the retarding force.
There has been debate over the years whether it is better for a derailed train to become separated to keep the derailing cars from pulling others with it. In this case, my feeling is that the safety chains probably saved passengers from more serious injuries because it helped keep the cars from overturning or overriding/telescoping each other.
Regardless of the root cause of splitting the switch, White Pass was lucky and dodged a bullet on this one. It potentially could have been far worse.
My opinion ...