Landslides is one of the most destructive geological hazards in the world today. Due to the high speeds that slides can reach, up to 160 km/hour (100 mph) and the debris they carry with them, Debris Flow is capable of burying entire towns and communities, covering roads, causing death and injury, destroying property and bringing all transportation to a halt.
So how do we deal with them?
Debris flows, different from landslides and mudflows, are made up of "loose" particles that move independently within the flow. Mud flows are composed of mud and water, whereas debris flows are made up larger particles. It has been estimated that at least 50% of the particles contained within a debris flow are made-up of sand-sized or larger particles (i.e. rocks, trees, etc).
Causes of Flows:
Debris flows can be triggered in a number of ways. Typically, they result from sudden rainfall, where water begins to wash material from a slope, or when water removed material from a freshly burned stretch of land. A rapid snowmelt can also be a cause, where newly-melted snow water is channeled over a steep valley filled with debris that is loose enough to be mobilized.
Another major cause of debris flows is the erosion of steams and riverbanks. As flowing water gradually causes the banks to collapse, the erosion can cut into thick deposits of saturated materials stacked up against the valley walls. This erosion removes support from the base of the slope and can trigger a sudden flow of debris.
In some cases, debris flows originate from older landslides. These can take the form of unstable masses perched atop a steep slope. After being lubricated by a flow of water over the top of the old landslide, the slide material or erosion at the base can remove support and trigger a flow.
Some debris flows occur as a result of wildfires or deforestation, where vegetation is burned or stripped from a steep slope. Prior to this, the vegetation's roots anchored the soil and removed absorbed water. The loss of this support leads to the accumulation of moisture which can result in structural failure, followed by a flow.
In addition, replanting forests on hillsides to anchor the soil, as well as monitoring hilly areas that have recently suffered from wildfires is a good preventative measure.
Read more at: https://phys.org/news/2016-09-debris.html#jCp