General mechanism of a landslide
Diagram of the apparatus used to monitor Pore Water Pressure
Pore Water Pressure
Pore Water Pressure is the key to monitoring landslides. Pore water pressure is the pressure that develops as water fills in the pore spaces inbetween particles. Shear strength, a resisting force, decreases and the weight, a driving force, increases. The safety factor becomes less than one and a movement becomes possible.
Equipment such as this measures the Deep Pore Pressure and Shallow Pore Pressure. Data received from one of these monitors may look like this.
"Steady change in the extensometer output (vertical axis) indicates downslope movement, brief changes that return to a constant value, such as the spikes in the graph of E-4 (yellow), usually result from physical or electrical disturbances and do not indicate movement."