NYT:
By some estimates, about 100,000 people were crammed together near midnight to celebrate the holiday of Lag b’Omer, when ultra-Orthodox Jews traditionally convene at the tomb of a prominent rabbi from antiquity on Mount Meron. The festivities include dancing and bonfires.
....
Some said people started fleeing after either a grandstand or a roof collapsed. Others said some of the celebrants had slipped on some steps, setting off what the news site Ynet described as a “human avalanche.”