I recall driving US-101 in Oregon some years back and kept seeing "Tsunami evacuation route" signs.
https://www.oregon.gov/oem/Documents/Tsunami_Evacuation_Sign...
On the bright side, you won't need a siren, If the ground drops by 10 meters over the course of 5 minutes and you can't stand up because of the shaking, you can be sure a tsunamui up to 30 meters high will be there in an hour or two.
The remark is clearly only intended to give an impression of the magnitude of the worst-case scenario.
Eruption-related lahars and sedimentation response downstream of Mount Hood: Field guide to volcaniclastic deposits along the Sandy River, Oregon -- https://volcanoes.usgs.gov/vsc/file_mngr/file-59/Pierson%20e...
> The Sandy River was originally named the Quicksand River by Lewis and Clark in 1805 (Moulton and Dunlay, 1990). Expedition members noted that the river (a) was ~275 m wide at its mouth and for several kilometers upstream on the delta (30-150 m wide there today); (b) had a number of mid Channel Islands; and (c) had flow which was turbid and very shallow (resembling the Platte River in Nebraska, they noted). It was given its name because "the bed of this stream is formed entirely of quick sand."
https://pubs.usgs.gov/fs/old.2000/fs060-00/fs060-00.pdf
> What happened? The answer lay 50 miles away at Mount Hood. An eruption in the 1790's caused a tremendous amount of volcanic rock and sand to enter the Sandy River drainage. That sediment was still being flushed downstream when Lewis and Clark saw and named the river. Since 1806, the river has removed the excess sediment from its channel.
