Volcanoes are a major geologic force throughout the Pacific Northwest. Immensely powerful, they only periodically erupt, but may cause major havoc when they do.
Of Washington's five major active volcanoes: Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens and Mount Adams, only Mount Rainier and Mount St. Helens pose potential danger for those living the in the King County region.
While regional volcanoes are lie enough eastward of Vashon to not present a threat of lava and lahars (mud flows) that threaten communities closer to the Cascades crest, volcanic ash could easily affect Vashon residents if the winds were coming from an unusual direction.Find out more about issues with ash at: http://volcanoes.usgs.gov/ash/index.html
Disruptions could easily affect Tacoma and Seattle - with ripple effects affecting Vashon.
For a historical view of volcanoes (& earthquakes) worldwide look at: https://volcano.si.axismaps.io/