Materials left behind by a mudslide may keep ____ from going down as quickly.

Water.

Materials left behind by a mudslide may keep water from going down as quickly. 

Mudslides are natural disasters in which rocks, mud, soil, trees, etc. are detached from their original location and rapidly move down a slope. A mudslide can be triggered by a number of factors including heavy rainfall (most common), earthquakes, erosion by streams of water, human activities, volcanic eruptions, or alternate freezing and thawing of water. These events can cause the soil and rocks to become loose and move down a slope. This downward motion gains acceleration as it spreads and covers more and more area as it travels down. When caused by heavy rainfall, the soil becomes fully saturated with water and tends to move down natural channels in the slope. Not all of the material is carried down by the mudslide, some being left behind. This material will obstruct the path of water and may cause it to go down slowly.

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