Kettle holes can also form when a lake has a large amount of ice blocking the outlet where water drains from it, and the ice breaks up all at once. The flood that this causes can carry blocks of ice and sediment similar to the glacier-calf activity described above. These floods are called "jökulhlaups," an Islandic term used wherever this occurs. In 1992, the geologist Judith Maizels made outdoor observations and reproduced the conditions in a laboratory simulation. She found that protective walls (called ramparts) (protective walls) form around the edge of kettle holes made by jökulhlaup floods. The type of ramparts that develop depends on the how concentrated are the rock fragments contained in the melted ice block, and also on how deeply the block was buried by sediment.