Mass Movements

Turner Mason

Mr. Hoffman

L2K B104

10 October, 2013

Mass Movements

        Mass movements do not seem like a very threatening force of nature, but they take more lives than other natural disasters such as tornadoes. A mass movement is the movement of rocks or dirt down a slope, and it is usually caused by a weakness of the top layer of soil or rocks ("Landslide").

        A landslide is a type of mass movement, which is when sediment moves down a slope from the force of gravity. Mass movements can happen very fast in a matter of minutes, or very slow over a period of several years. Depending on the size of the weakened area, landslides can be very small such as a couple rocks sliding down a slope, or the whole side of a mountain falling off to the ground. A mass movement is caused when soil is separated from the bedrock that the soil or other substance sits on. The start of a mass movement then occurs when the force of gravity overcomes the force of friction. This separation is almost always caused from outside factors such as excessive rainfall. Bedrock is a very stable solid layer of rock so it will almost never move except in the case of an earthquake ("Landslide").

        The following are the four different types of mass movements: creeps, slumps, flows, and landslides. A creep is when the soil on top of the bedrock very slowly slides down the slope, and the process can take several years. Creeps are also not uncommon to find on gentle slopes unlike most other types of mass movements. The reason that creeps are so slow is because the connection of the sediment to the bedrock below it is not completely disjointed, but only slightly hampered. The main cause of creeps is from freezing in the winter and then thawing in the summer time. These two processes change the structure of the soil and its ability to cling to the bedrock ("Mass Wasting").

         The next type of mass movement is called a slump, and it is when one very large piece of sediment breaks off. The cause of this happening is from when the base of the sediment can no longer support the heavy sediment on top, and the bottom layer fails due to the major force of gravity. The reasons that the base of the sediment loses its ability to support the upper layer is because water from rainfall can increase the mass of the top layer. Water will also often erode the bottom layer away until the top layer falls. This is a much more dramatic and dangerous type of mass movement due to the speed at which it happens ("Mass Wasting").

        The last type of mass movement is called a flow, and it is caused from when very heavy rainfall mixes with loose sediment. As this flow moves down the mountain it picks up many other materials such as rocks and soil; and it will grow rapidly in size as it moves down the slope. Avalanches and mudflows are both example of flows, and they are probably the most dangerous type of mass movement due to how fast they can move over an area at speeds over 50 miles per hour (Miller).

        Lastly, human activity is another major cause of landslides. Since trees and their roots hold the top layer of sediment together, in areas where there are trees, the chance of landslides is greatly decreased. When humans take trees out of hilly areas, this connection is lost and mass movements are much more likely to happen ("Do People Have Any Influence over Whether Landslides Happen?").

        With all of the recent Colorado rain and flooding, quite a few of severe mass movements have happened in the area. When the flooding was happening, I looked at several videos of the damage and a lot of severe mass movements happened during this time. It was fascinating to watch them happen, and I wondered how they worked. After seeing all of the damage they did right in my backyard, I was inspired to write a log on this topic. Before writing this log, I did not know about the diversity of different types of mass movements. I did not even know what mass movements were, and that landslides are just a type of mass movement. I am a big weather guy, but until writing this log, I knew very little about some of the secondhand affects that weather causes on the ground. Now I see the true power of what weather can cause, and how mass movements are very closely related and caused by the weather in most cases.

        Before writing this log, I was also not aware that mass movements are such a popular occurrence in the world. Since landslides are rarely ever talked about, they do not seem to be very threatening, but now I know how dangerous these powerful disasters can be. I also had no clue about how mass movements are started. I figured that there was a cause, but I did not know that water was the most popular cause of mass movements happening. Overall, I am surprised at how little I knew about this topic before I wrote this log, and how much I know about mass movements now.