Lahars are a type of gravity driven mudflow or debris flow that originate on the slopes of a volcano.  They can be triggered by volcanic activity, for example, minor volcanic eruptions that melt glaciers, rainfall, breakout floods or other mechanisms.  These events all generate rapid discharge that can mobilize sediment, ash, rock and other debris and move quickly down the drainages on volcanic slopes.  Seasonal debris flows are common in the Tahoma Creek drainage on the SW side of Mt. Rainier and the north and west flanks of Mt. St. Helens.  The University of Oregon, USGS, and the PNSN recently deployed a dense array of seismometers in places where debris flows occur to record the seismic signature of these events.  The resulting data will be used to develop a framework to detect and quantify features of lahars and develop real-time warnings similar to the ShakeAlert earthquake early warning system.