LIQUEFACTION - DEFINED

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When loosely packed and wet sand is shaken during an earthquake, it may flow like liquid. This is called liquefaction. Anyone who has walked on a beach may have seen a small-scale version of this process. Stamp your foot in the sand near the water’s edge and suddenly the area of your footprint vibrates like gelatin.

Earthquake-induced liquefaction is often accompanied by cracks in the ground surface and small eruptions of sand and water called sand blows. During the 2002 Denali Fault earthquake, people in Northway watched sand erupting 4 feet out of the ground. When a soil liquefies, it is unable to support the weight of the ground or any structures above it. Bridges and buildings may settle and tilt even though they withstood strong ground shaking. If the liquefied area is on a slope, massive landslides may result.

The Bootlegger Cove Formation is the name of a soil that underlies much of Anchorage. Liquefaction of a part of the Bootlegger Cove Formation caused much of the destruction in the Anchorage area during the 1964 earthquake, and it causes people to feel earthquakes more strongly in western Anchorage. Soils that liquefy are not limited to the Anchorage area, but are present in many low-lying parts of Alaska where soil near the surface is saturated with water.