In the county directly south of me (Pierce county, Washington), a Lahar Warning system was set up 15 years ago in 1998, the original system consisted of 9 Whelen Public Services 3016 electronic sirens, 4 Federal Signal 2001 electro-mechanical sirens, 1 Whelen Vortex R4 electronic siren, and 1 Federal Signal 2T22 electro-mechanical siren. If you don't know what a Lahar is, a Lahar is a Volcanic Mudflow consisting of Ash, melted ice, Pumice, and superheated Pyroclasts that are created when Lava shoots out the crater of the volcano (Mount Rainier in this case), flows down the sides of the mountain, the mixes with melting ice and ash to form fast-moving sweeps of superheated mud, which will disintegrate everything in it's path.
The sirens were set up to warn the entire Puyallup River valley of one of these incoming monsters, signals of an incoming flow are picked up by 5 Acoustic Flow Monitors set up around the base of Mount Rainier, these monitors can also pick up seismic activity around the mountain. Lahars like this can be generated from Landslides, Flank Collapses of the mountain's crater, Avalanches, Earthquakes, and Volcanic Eruptions in general. Other than the original system being put in, three Fire sirens in the area are also used to warn of Volcanic Lahars, 2 of which have been deactivated, those were the Federal Signal Model 5 siren in Milton and the Federal Signal Model 2 siren in Orting (M2 has been replaced).
As of 2008, as part of a 10-year upgrade, most of the older CD sirens have been replaced by Federal Signal Modulator electronic sirens, about 17 of these went up throughout the valley. Now only 5 Whelen 3016 sirens, 3 2001 sirens, the Whelen Vortex R4, and an older Federal Fire siren remain in the system, with the additional Modulator sirens, as of April 2013, all the older sirens were silenced.
Whenever more information is received, I will update this post!
