“As we were walking towards Al Jamarat, the flow suddenly stopped withUm, I don't get why a "stop in the flow" is enough to cause a "stampede". The ones who push from behind may cause some concern among those who cannot move forward, but why do they keep pushing if it's achieving nothing? I think there must be some strange laws of crowd behaviour I don't understand here.
an apparent reason,” Mohammad, a pilgrim, told Sabq. “A few minutes
later, a large group of people came from the back and pushed us, causing
the stampede. Women started to cry and several old people fell on the
ground. Only the intervention of the security and medical authorities
saved us from a bigger tragedy,” said Mohammad who was still being
treated for his injuries.
Update: this explanation at the ABC suggests it might be more of a case of a "crowd crush" than a "stampede". Which would make a bit more sense. Still, it seems a bit odd to me that crowds, when not worried about escaping from a danger, simply can't stop when it's obvious no one is moving...
Update 2: some more detailed discussion of how crowd crushes happen is at Wired.