Rumble. Rumble. The roaring grows. Suddenly a wall of boulders, trees, rocks, and mud appears around a bend in a narrow canyon. More than 100 Californias have been killed by debris flows during the past 25 years. Most of these 100 deaths occurred when debris flows buried persons who were sleeping in lower-floor bedrooms that were adjacent to hazardous slopes. California has lots of mudslides.
Mudslides disrupt electric, water, sewer and gas lines. They wash out roads and create health problems when sewage or flood water spills down hillsides, often contaminating drinking water.
Power lines and fallen tree limbs can be dangerous and can cause electric shock. Alternate heat sources used improperly can lead to death or illness from fire or carbon monoxide poisoning.
Mudslides are also associated with volcanoes and earthquakes and can result in respiratory problems due to breathing of ash, fumes, heat or gases.
A mudflow or mudslide is the most rapid of up to 50 mph and fluid type of downhill mass wasting. The mass of stuff finds the stream channel at the bottom of the canyon and continues its destructive journey to the bottom of the mountain. Mudslides contain more water than landslides. They can contain solid material, too, but generally have fewer large rocks and trees than landslides. Mudslide consistency is a lot like cake batter -- with a few sticks and pebbles thrown in.
Heavy rains and rapid snowmelt can trigger mud flows on unstable slopes. Mudslides formed after Mount St. Helens erupted, because the heat and lava quickly melted the snow blanketing the mountain. Mudslides usually start on steep slopes and can be activated by natural disasters. Areas where wildfires or human modification of the land have destroyed vegetation on slopes are particularly vulnerable to landslides during and after heavyrains
Wildfires can also lead to destructive debris-flow activity. In July 1994, a severe wildfire swept Storm King Mountain, west of Glenwood Springs, Colorado, denuding the slopes of vegetation. Heavy rains on the mountain in September resulted in numerous debris flows, one of which blocked Interstate 70 and threatened to dam the Colorado River.
Some landslides move slowly and cause damage gradually, whereas others move so rapidly that they can destroy property and take lives suddenly and unexpectedly. Gravity is the force driving landslide movement. Factors that allow the force of gravity to overcome the resistance of earth material to landslide movement include: saturation by water, steepening of slopes by erosion or construction, alternate freezing or thawing, earthquake shaking, and volcanic eruptions.
Landslides are typically associated with periods of heavy rainfall or rapid snow melt and tend to worsen the effects of flooding that often accompanies these events. In areas burned by forest and brush fires, a lower threshold of precipitation may initiate landslides.
The health hazards associated with landslides and mudflows include, rapidly moving water and debris that can lead to trauma, broken electrical, water, gas, and sewage lines that can result in injury or illness, and disrupted roadways and railways that can endanger motorists and disrupt transport and access to health care.
The single most important action that should be taken by residents on rainy nights is NOT to sleep in lower-floor bedrooms on the sides of houses that face hazardous slopes.
Know about the hazard potential where you live, take steps to reduce your risk, and practice preparedness plans. Better yet, move to Kingman, Arizona and get away from the mud slides.