A lahar is an avalanche of mud, rocks and water that has the consistency of thick concrete. It moves at a fast speed, taking many people by surprise and causing great destruction and loss of life. During the eruption of Nevado del Ruiz in Colombia in 1985, over 23,000 people died in the town of Armero from lahars unleashed by the eruption. Since Lahars are basically flowing concrete, they simply roll over anything and everything in their path. They will typically flow down river valleys which give them a clear path and exacerbate the threat they pose. 
 
When Nevado del Ruiz erupted in Colombia in 1985, it became one of the most destructive volcanic eruptions in history. Several towns were situated close to the volcano and were in the path of dangerous lahars that flowed down the mountainside after the eruption. They did not have enough warning or any time to out run the lahars and 23,000 people were lost in the town of Armero in the tragedy. 
 
Hiroyuki Tanaka from the University of Tokyo engineered a technique to utilize muons, a decay product from cosmic rays, to penetrate through miles of rock to obtain images of the inside of volcanoes. Muons can penetrate through entire mountains and provide a graphic of the structure within unlike any method seen before by scientists. Using muons to see through rock, scientists, such as with the study of Vesuvius and Mount Asama, can obtain and image of the interior of a volcano and use the data collected to predict volcanic activity.
