I've been to Mt St Helens several times, since the eruption, and the evidence of the awesome power of the devastation is almost unbelievable. There's one campsite we go to near Ghost Lake and it's on the fringe of the blast zone and you can see trees that are still standing that have been scoured smooth on the mountain facing side and intact on the opposite side. The level of Spirit Lake rose 600 feet that day. There is a raft of logs of downed trees that wanders about on the surface of the lake like a little swirl of foam on your mocha, but it's hundreds of giant logs. If you make a trip to the park, be sure to go all the way to the end of the road and stop in at the
Johnstone Ridge Observatory center. It is extremely informative and entertaining.
It's not "Seattle" exactly, but an incredible trip, very worthwhile. Highly recommended.