LAHARS

   Lahar is a word in Indonesian meaning Lava or mudflow..Lahars are like pyroclastic flows but have more water.Lahars form from debris avalanches that contain water from the snow and ice which mixes with loos debris.It also forms from pyroclastic flows that mix themselves with river water when they travel downslope.Lahars almost always travel down valleys.They usually travel at velocities of 1 m/s to 40 m/s. The velocity usually depends on channel width and slope,volume of flow, and grain size composition.

                                 MT.RAINIERMt.Rainier's hazards include crevasses, avalanches, and rock falls . Lahars aren't a huge risk unless there is a huge mudslide or eruption. The Puyallup River Valley is formed by the 500 year old Electron Lahar.Lahars can travel tens of miles from Mt.Rainier and reach Puget Sound. As you can see on the map above, a lahar from Mt. Rainier can get to Yelm, Puyallup, and even as far as Tacoma!

        The largest Lahar coming from Mt.Rainier in the last 10,000 years was the Osceola Mudflow. 6 other smaller lahars have happened in the last 5,600 years. The Osceola Mudflow was 10 times larger than any other mudflow coming from Mt. Rainier.  About 5,600 years ago, Mt.Rainier had a Catastrophic collapse similar to the much smaller collapse of Mt.St. Helens on May 18, 1980. The Debris from this mudflow caused the Osceola and the Paradise mudflows. These mudflows had traveled down the White and Nisqually Rivers, reached Puget Sound and pushed out the shoreline several miles.

http://www.geo.mtu.edu/volcanoes/hazards/primer/lahar.html

http://vulcan.wr.usgs.gov/Volcanoes/Rainier/Lahars/Historical/description_paradise.html