plasticoviscous deformation

Plasticoviscous deformation describes a material's response to stress, combining both plastic and viscous behaviors. Initially, the material behaves elastically, returning to its original shape when the stress is removed. However, once a certain yield point stress is reached, the material undergoes continuous, permanent deformation, similar to a viscous fluid. This means it flows under sustained force without fracturing.12

This type of deformation is significant in geological processes, such as the movement and flow of rocks under high temperature and pressure, which shapes the Earth's surface over millions of years. It is also relevant in understanding the behavior of materials like ice and certain rocks at depth, where slow, permanent deformation occurs over long periods under constant load.31