We commonly think of rocks as strong, solid materials, which can possibly break when squeezed or stretched hard enough. However, most rocks can deform in a viscous manner, that is, accumulate deformation over time at loads that are smaller than their ultimate failure strength. At elevated temperature and pressure, such as in the Earth's mantle and lower crust, the processes at the origin of viscous flow of rocks are similar to those in metals: the crystals forming the rocks deform by atomic scale processes linked to motion of crystal defects. At shallow depth, such as in the upper 10km of the Earth's crust, viscous flow may originate from well established chemical processes, such as dissolution and precipitation of minerals. However, even in apparently "dry" and "cold" conditions, rocks also creep, likely due to sliding between grains and slow growth of microcracks.
Much of the evidence for these creep phenomena can be found in Nature, for instance from geophysical or geological observations. Here, I will give an overview of creep processes in rocks from the point of view of laboratory experiments, which allow us to identify the exact creep mechanisms and determine mathematical representations of them that we can extrapolate to the natural scale. The lecture will cover some of the experimental devices and tools that have been developed to study rock deformation, and how this field draws from a wide range of disciplines to make progress towards a better understanding of our planet.