Bradyseism is the gradual uplift (positive bradyseism) or descent (negative bradyseism) of part of the Earth's surface caused by the filling or emptying of an underground
magma chamber and/or hydrothermal activity, particularly in volcanic
calderas. It can persist for millennia in between eruptions and each uplift event is normally accompanied by thousands of small to moderate
earthquakes. The word derives from the
ancient Greek words "bradus", meaning 'slow', and "seism" meaning 'movement', and was coined by
Arturo Issel in 1883.