In geology, solifluction, also known as soil fluction, is a type of mass wasting where waterlogged sediment moves slowly downslope, over impermeable material. It occurs in periglacial environments where melting during the warm season leads to water saturation in the thawed surface material (active layer), causing a form of downslope "flow" to occur. This "flow" is due to frost heave that occurs normal to the slope, as well as to small-scale slippage. Where the underlying ground is permanently frozen (permafrost) the process is often called gelifluction.