One month after its launch, the collapse of an enormous lava dome upon the Soufriere Hills Volcano on the Caribbean island of Montserrat put a notable aspect of CALIPSO to good use: detecting and tracking volcanic plumes. The ash clouds of this volcano traveled all the way to the lower stratosphere, which can put air traffic at risk. This fascinating feature of CALIPSO allowed it to locate and examine the properties of the aerosols mixed in the volcanic clouds.