[2] The observatory is named for United States Geological Survey (USGS) volcanologist David A. Johnston, who was killed by the 1980 eruption of Mount St.

[3] The observatory's current territory covers Oregon, Washington, and Idaho.

[4] The Cascades Volcano Observatory is part of the USGS, a scientific agency of the United States government.

[5] It is located in Vancouver, Washington in the Portland, Oregon metropolitan area.

USGS has noted, though less probable, that it is still possible for volcanoes to erupt on longer intervals than mentioned.