One thing we know for certain especially about the Cascadia volcano system: these things erupt frequently and when they do, they often blow up and are very deformed by these eruptions, they are not Mt. Fuji style in appearance. So we must assume that if they do erupt, they might have massive landslide collapses like Mt. St. Helens. This means that a major city and several smaller ones can be not only flooded badly by lahars but as these hit the Puget Sound, they will, no question about this, cause tsunamis. Which few people want to think about in that region.