Lahars
A Lahar is a destructive mudflow on the slopes of a volcano.
Lahars always follow behind a volcano's eruption. They can crush buildings people and other objects in there way.
Lahars are almost always preceded by volcanic unrest, so in most cases there will be time to warn people when there is an increased chance of a lahar. Obtain a National Oceanic and Atmospheric Administration (NOAA) weather radio to receive alerts about possible lahars, as well as other natural hazards
This is a picture of a lahar following after the eruption of a volcano.
volcano eruptions are very devastating but since a lahar always will always follow it is two times a deadly. So be carful, because if a volcano erupts it will still never be safe because of the lahar afterwards.
The pick above shows that lahars basically looks like hardened magma when it dries up.
bibliography:http://volcanology.geol.ucsb.edu/lahar.htm
http://volcanoes.usgs.gov/hazards/lahar/index.php
http://geology.com/usgs/rainier/
http://volcanoes.usgs.gov/hazards/lahar/index.php
http://geology.com/usgs/rainier/