The Land Is Sliding.

          From earthquakes, flooding, and volcanoes, we continue the chaine of earth’s geological events on the blog this week by introducing Mass Wasting.

Mass wasting is the process of erosion whereby rock, soil, and other earth materials move down a slope because of gravitational forces. It proceeds at variable rates of speed and is largely dependent on the water saturation levels and the steepness of the terrain. A destructive, rapid mass‐wasting event is called a landslide; if the movement is slow enough that it cannot be seen in motion, it is called creep. Three kinds of movement are generally recognized: flow, slip, and fall. A mass‐wasting event is called a flow if the mass moves downslope like a viscous fluid. If the mass moves as a solid unit along a surface or plane, it is called a slip. A slip that moves along a surface parallel to the slope is called a slide. If the movement occurs along a curved surface where the downward movement of the upper part of the mass leaves a steep scarp (cliff) and the bottom part is pushed outward along a more horizontal plane, it is called a slump. Earth material that free‐falls from a steep face or cliff is termed a fall.  https://www.cliffsnotes.com/study-guides/geology/mass-wasting/introduction-to-mass-wasting 

     To pinpoint dangerous regions, geologists look for landforms known to result from mass movements, for where these movements have happened in the past, they might happen again in the future. Features such as slump head scarps, swaths of forest in which trees have been tilted, piles of loose debris at the base of hills, and hummocky land surfaces all indicate recent mass wasting.

In some cases, geologists may also be able to detect regions that are beginning to move. For example :

·         roads, buildings, and pipes begin to crack over unstable ground.

·         Power lines may be too tight or too loose because the poles to which they are attached move together or apart. 

·         Visible cracks form on the ground at the potential head of a slump, and the ground may bulge up at the toe of the slump.

·         In some cases, subsurface cracks may drain the water from an area and kill off vegetation, whereas in other areas land may sink and form a swamp. 

·         Slow movements cause trees to develop pronounced curves at their base. 

More recently, new extremely precise surveying technologies have permitted geologists to detect the beginnings of mass movements that may not yet have visibly affected the land surface.http://geologylearn.blogspot.com/2015/12/how-can-we-protect-against-mass.html 

       Mass wasting events are caused by gravity in combination with a variety of geologic, climatic, and in some cases human factors. One other factor which is often associated with dramatic mass wasting events is vegetative cover and particularly sudden changes to vegetative cover by fire or human activities. Particularly large scale mass wasting events frequently follow forest fires and heavy rains on steep slopes. Although it is impossible to anticipate all mass wasting events being aware of the factors which contribute to such events is essential to avoiding them.

       Climate can have a dramatic influence on mass wasting events. Areas with a moist temperate climate are subjected to frequent freeze and thaw cycles. Freeze-thaw cycles affect rocks because when water seeps into cracks in a rock and then freezes it expands putting tremendous pressure (24 tons per ft2) on the rock, forcing the cracks to expand. Over time this type of physical weathering can cause even the strongest rocks to break apart. Sometimes this process is referred to as frost heaving or freeze thaw action. Thermal expansion and contraction of rock bodies also may occur in areas with extreme temperature variations and this likewise affects the stability of rock. Moisture, in addition to its influence through freeze thaw cycles (physical weathering,) can actually dissolve some of the minerals that rocks are made of. This is called chemical weathering and it also affects the stability of rocks. Sometimes large mass wasting events (or large numbers of smaller events) are associated with heavy rains. Heavy precipitation can initiate certain types of mass wasting by creating hydrostatic pressure and serve to lubricate slides once they are in motion.

      Certain human activities are known to affect mass wasting, many of the potential problems can be avoided by using good land use planning techniques and engineering solutions where appropriate. Drainage diversion and irrigation projects may destabilize slopes and increase the probability of mass wasting by increasing the moisture in vulnerable areas. Likewise hillside excavation which changes slope gradient could destabilize slopes making them prone to mass wasting. Blasting, often associated with mining or construction activities, can result in vibrations and air blasts which may trigger mass wasting events. Other human activities which could potentially impact mass wasting include transportation vibration, increasing the load that the ground must bear (especially on slopes,) changing vegetative cover, and pumping. https://www.nature.nps.gov/geology/hazards/mass_wasting.cfm 

     Mass Wasting in my country, Morocco, is common even though it isn’t reported in the media; mostly because they happen in remote ares where the people don’t live. Unless it occurred in a known place.

The only time that I was able to see what mass wasting could cause as damages, was in the city where I lived in Morocco, couple of block from my house. It happened in 2007, when a project of buildings was under construction in a land that turns into a small lake during heavy rain in the winter. The team responsible for the project decided it was a good idea to create a wall of rock to stop the water from gathering in that location, and at the same time it will enforce the land. What they didn't know, or ignored, was that the land was already soaked with water. When they start building the complex, the land couldn’t handle the weight on top of it, so it slides bringing the buildings with her to the ground; leaving multiple deaths and a completely useful site. Till this day, the authorities can’t go into the site to remove the debris or demolish the rest of the buildings because they don’t what will happen. Instead, they surrounded the area with a metal like a wall so no one will enter it.

    An anther mass wasting that was i able to find was in Arroumd ( central Atlas Mountains of Morocco) as a Rock Avalanche.  The landslide itself have originated from the steep slopes in the background, traveled down the side valley and been deposited in the valley floor and in part in the main valley.  The resulting deposit has blocked the main valley to a degree. The image below shows the landslide deposit and the village from upstream. 

http://blogs.agu.org/landslideblog/2014/04/16/arroumd/ 

To prevent mass wasting,

Morocco has a region which is known for having many landslides. The Zoumi sector of the Moroccan Rif was used in a study because of the frequency and distribution of the landslides that take place.

 

The idea behind the study was to create a susceptibility map. This map will assist in providing needed information to better plan, protect the people and property when it comes to the rebuilding of structures and roads after the occurrence of such mass movements.

http://madonnamorocco2015.blogspot.com/2015/10/mass-wasting_63.html

1. Avoidance is the best method for limiting mass wasting hazards. It is recommended that people stay away from and limit development in areas prone to rock falls and landslides if possible.
2. Good land use and geohazard planning employing appropriate geologic maps is recommended prior to development activity in areas prone to mass wasting.
3. Engineering solutions may be appropriate for minimizing mass wasting hazards in certain situations, examples of such solutions include; removing the hazard through blasting or stabilizing the hazard using, rock bolts, mesh, steel, retaining walls, gabions, tension cables, grout, drains, etc. Other engineering solutions may not eliminate or stabilize the hazard but rather work to minimize or control rock fall and landslide run-out areas with ditches, specially designed tension cable nets, and talus walls.
4. Ensuring that projects in mass wasting prone areas have proper drainage is also crucial to minimizing potential hazards.
5. Proper maintenance and inspection of mass wasting prone areas is essential to spotting potential hazards.

https://www.nature.nps.gov/geology/hazards/mass_wasting.cfm