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Our transcription: The tragedy in Armero is an extreme example of the geologic process known as "mass wasting," the downslope movement of Earth materials under the influence of gravity. Mass wasting can take many forms, from a deadly mudflow rushing down a mountain slope, such as we saw at Armero, to destructive landslides such as this one, which in a few second delivered tons of debris, including these boulders onto the road below, to more subtle forms in which the downslope movement is almost imperceptible. Slopes are the most common of landforms, so mass wasting operates over virtually the entire surface of the Earth. Think of mass wasting as a continuous chain of processes that move Earth materials from the tops of the highest mountains down to the deep ocean floor. The two driving forces behind mass wasting are tectonic activity, the uplift and mountain building that continuously maintains the slopes, and gravity, which tends to pull the slopes down even out the landscape. Mass wasting is a natural process that continuously shapes the landscape, and it occurs without human involvement. However, it's important for us to recognize that our decisions, such as where we build our roads and structures, and the ways in which we alter natural landscapes can affect this process and sometimes trigger mass wasting events.
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