What are the cause and effect of liquifaction?

Answer 1

Liquefaction is when a volume of densely packed material like sand or soil is infiltrated with enough water or fluid that the material loosens and begins to "flow" in an almost liquid fashion.

There were many examples of this in the huge earthquake that hit Japan recently. The earth beneath roads and structures became so saturated with sea water that whole sections of sidewalk or road would shift and roll with the changing water pressure. Here is one of the best videos on YouTube showing the slow movements of liquifaction during that event:

Liquefaction can also be responsible for landslides....

Another form of liquifaction is when a dry material can flow. This happens when the material has a smooth shape to each individual particle. Then it can't bind to itself and can flow in a very similar way to particles mixed with water.

You can experiment with grain smoothness and liquifaction by using ordinary play sand. Try piling it up dry. How high can you go when it's dry? How high can it go if you use wet sand? What happens if you push a water hose into one side of your hill and turn the water on low?

Grains of sand are not smooth at all and because they are so angular, they can settle into piles that don't flow too much, even when slightly wet. But, if you introduce enough water to overcome that angularity, the sand will flow and your hills will collapse.