Eruption Style:

Nevado del Ruiz is an explosive, active, stratovolcano. Stratovolcanos form at a convergent plate margins, and have steep summit slopes and a surprisingly small crater. They are generally known as composite cones for their layered, cone shape appearance. They typically have a layered appearance with alternating lava flows, air fall tephra, pyroclastic flows, volcanic mudflows known as lahars, and debris flows. Nevado del Ruiz produces andesitic and dacitic lava, as well as andesitic pyroclastics. These pyroclastic and lava flows can abolish everything in their path, and travel for miles. Much debris and ash is also ejected from this volcano when it erupts. Lahars are one of the most deadly consequences of Nevado del Ruiz during an eruption. As hot pyroclastic flows sweep down the sides of Nevado del Ruiz, it causes a rapid melting of snow and ice and creates very large floods that sweep down the volcano and through valleys. As these floods flow more quickly, they pick up loose debris and soil, growing in density and volume to form extremely hot mood flows (lahars). These lahars can be as large as 50 meters thick and travel over 50 km per hour. They destroy everything surrounding them, and are the cause of thousands of deaths and destruction of cities. Many hazards come with a Nevado del Ruiz eruption, all harmful, and many deadly. Below is a picture of a lahar from Nevado del Ruiz's 1985 eruption.

http://membres.lycos.fr/lahars/resume2.jpg