1. The forcible loss or a violent separation of a body part from another one, either by surgery or as a result of a trauma or physical injury in traffic casualties, industrial mishaps, domestic afflictions, shootings, stabbings, etc.: After the terrible car accident, Mr. Smith had to have an avulsion performed at the hospital which resulted in having his left foot removed.
2. A sudden change in the course of a river; usually, from one channel to another one: After months of rain and strong winds, the meandering stream went through an avulsion by rapidly altering its route and going around the back of the farm and not by the front as before.
3. The violent movement of soil from one property to another as a result of a flood or a shift in the course of a boundary stream: The earthquake caused an avulsion in the coastal area of California and some land sank considerably in some places and created more land in other areas.