Lake elevation monitoring gage on Spirit Lake, Mount St. Helens. Do...

The USGS operates a real-time lake elevation monitoring gage on Spirit Lake to ensure water level does not exceed a safe limit. In 1985, the U.S. Army Corps of Engineers completed a tunnel under Harry's Ridge into the South Coldwater Creek valley to serve as the lake outlet, and to prevent the lake from rising and spilling over easily eroded debris avalanche deposits.