 It is not uncommon for large boulders to fall off the Bürgenstock into Lake Lucerne, though this presents little risk of a tsunami because of the relatively low amount of energy released in such falls.A study by a team from the University of Geneva, led by Stéphanie Girardclos and Guy Simpson, has found that the tsunami of 563 may not have been directly caused by the landslide, but by the collapse of sediments on the lake bed.The team found a giant fan of turbidite – a mixture of sand and mud deposited by a rapid flow of water – spread across the lake bed.