Analogue Model for the Gravity Sliding of Sediments

Abstract

The gravity-driven sliding of soft sediments is modeled using a simple and reusable experiment. Sand, mud and water are shaken in a sealed plastic bottle. When the sand has partially settled, the bottle is tilted by several degrees and left on a stable surface for several hours, until a layer of mud is deposited above the gently dipping sand surface. Gentle squeezing or tapping of the bottle causes the sand to liquefy and pack more closely. Water is expelled from the sand and becomes trapped beneath, and therefore supports, the mud. The water beneath the mud becomes overpressured because it supports the weight of the mud. Friction between the mud and sand drops to zero, so the mud slides under gravity. Extensional structures develop towards the top of the slope, and buckle folds and thrusts develop in the mud towards the bottom of the slope. The experiment illustrates how earthquakes or storms can trigger liquefaction and overpressuring, and therefore gravity sliding of soft sediments.