 The breakup of this ice dam would send a violent wall of water, ice and debris down the river valley causing massive flooding and sometimes devastation to local settlers' properties.The jökulhlaup occurred annually until it ceased in 1967 due to glacial recession, thought to be associated with the massive Good Friday earthquake of 1964.Early pioneers were said to hold a yearly lottery, gambling on the exact date when the jökulhlaup would break and flood the Knik River Valley.