What is Quick Clay?

Quick clay is a type of marine clay with a very high water content that is subject to liquefaction when it is disturbed. This unusual clay is primarily found in the upper regions of the Northern Hemisphere, in places like Canada, Sweden, Norway, and Russia. It presents a significant safety hazard, as it can cause landslides and other public safety issues. The clay is often covered with a layer of seemingly stable topsoil, making it hard to spot when people are surveying an area for geologic hazards.

This clay consists of very fine particles of clay mixed with significant amounts of water. Surface tension creates a matrix, holding it together in a somewhat gelatinous state. When the surface tension is disrupted, as when the clay is agitated by an earthquake or by human activities like digging, the quick clay liquefies, turning into an oozing substance instead of a firm gel. This can be catastrophic if the clay happens to be in the wrong place.

In a quick clay landslide, disturbed clay starts to ooze down a mountain or hill, carrying topsoil and anything on it, such as homes and trees, along with it. The landslide will continue until the landscape flattens out or the clay encounters an obstacle. Such landslides are a big concern in geologically active areas, as the clay can be disturbed during earthquakes, even relatively small ones. Construction can also pose risks, as agitation from pile driving, digging, or heavy equipment may liquefy quick clay and turn a construction site into a landslide.

Known in some regions as Leda clay, quick clay can be tough to identify. When it is visible, soil samples will show the liquefaction tendency, but when it is covered with other layers of material, it is harder to find on a survey. Surveyors may clear an area for construction or other activities, not realizing that the underlying substrate is quick clay. Once a quick clay landslide starts, it can set off a chain reaction, disturbing other loose soils and clays in the area and creating a major disaster.

This clay appears to be millions of years old in many places, dating back to significant periods of glaciation. When glaciers slid across the surface of the earth, they ground up rock and soil into very fine particles, perfect for creating a suspension of clay and water like that seen with quick clay.