Mass Wasting is the down-slope (down-gradient) mass movement of Earth Materials, e.g., rock, sediments, mud, soil (and its associated plants), due to gravity and various "Triggering Events". It is part of the Natural Processes that reshape the land and includes characteristics of both Erosion and Deposition.
Though it is a Natural Process, we humans often play a role in facilitating the conditions leading up to the Triggering Events. Mass Wasting is one of those aspects of Earth Science that average people can learn for themselves, in an effort to avoid hazards and point them out to others, including authorities. The idea is not to live in fear, but to be educated and aware of the subtle warnings that Mother Nature often gives us. In other words, you don't have to be an Engineer to be aware.
Figure 1.
Sometimes, we can use "construction materials" as ways to illustrate Earth Processes. A couple of reasons are; 1) The setting is on a small scale and easily-observed; 2) There is no soil/vegetation cover; 3) In the cases of Figures 5 & 7 below, the piles are fresh, dry, and devoid of the Cohesion of clays. In this case, the pile of sand is of a uniform size, better still for illustrating the "Angle of Repose".
In regard to "Angle of Repose", different scientists will use somewhat different terms to define it, so you may need to read multiple sources before you completely understand the term. [And take notes to help you remember.]
The Angle of Repose is basically a natural angle of stability for earth materials. Strahler and Strahler (1997) define it in their Glossary as: "natural surface inclination (dip) of a slope consisting of loose, coarse, well-sorted rock or mineral fragments ... ". For loose, well-sorted, dry sand, the natural Angle of Repose is about 35 degrees. The degree of Angularity can affect how the grains "lock" against each other to support the slope. A pile of .5 mm diameter well-rounded beach sand will have a slightly lower Angle of Repose than a pile of .5 mm diameter angular river sand or quarry-crushed rock. Larger angular (or rough) clasts can support steeper angles, e.g., Cinder Cone slopes, Talus Slopes, and Talus Cones. (Figures 10 & 11 show Talus slopes and Talus Cones)
In the image of this construction sand pile (and Figure 6), you can see how the numerous, tiny landslides are "trying" to stabilize this "over-steepened", unnatural slope. When humans cut into the "Toe" of a natural slope, it removes that natural support at the base and it "Oversteepens" the slope.
Figure 2.
Figure 3.
Arid Climate Weathering is different from Humid Climate Weathering, partially because Chemical Weathering plays a bigger role in Humid Climates, whereas Physical Weathering plays a bigger role in Arid Climates. Monument Valley is a good place to illustrate Arid Climate Weathering. [Perhaps this video will help explain.]
In the arid climate of Monument Valley, the Organ Rock Shale forms a relatively-stable slope, easily seen from a distance. In this and other arid climates, cliffs are usually either Sandstones or Limestones. Unlike humid climates where rainfall and natural acids readily dissolve carbonate minerals, when it does rain, the dissolved carbonate in the water doesn't travel far, i.e., when water evaporates, fractures in the limestone are "repaired" as the dissolved-carbonate re-solidifies.
Using the Oklahoma example above: Here is a naturally-eroded slope and cliff "combo". The top of the Cliff could be referred to as the "Head", while the base could be referred to as the "Toe" (per the usage of some people). In the case of Figure 2, the "Toe" of the slope rests upon the somewhat stable floodplain of the Cimarron River.
If the Permian Flower Pot Shale was well-lithified, it would better "support" the gypsum cliffs of the overlying Blaine Formation. But as the Flower Pot Shale appears to be not-well-lithified and because Oklahoma's rainfall is higher than that of Monument Valley, Rockfalls are going to be a persistent occurrence at this site. Based upon the size and concentration of fallen clasts at the base of the cliff and/or slope, one could make a "snap judgment" of the frequency of rockfalls. In other words, pitching a tent at the base of the slopes would be a bad idea, besides, the floodplain at that site is very narrow.
Figure 4.
In the "Book Cliffs" image above, there are three "sets" of cliffs, underlain by shales in the upper portions of the exposure. Below is a long slope with the base obscured. It might be difficult to estimate a frequency of rockfalls, but I have pointed out two evident future rockfalls.
Figure 5.
The scene above is fairly common in the "Four Corners area". Similar to the Oklahoma image (Figure 2), just in a drier climate.
Figure 6.
Figure 7.
"Saprolite" literally means "rotten rock". Making an unsupported vertical construction cut in Saprolite is a bad idea. Others may differ, but because this mass didn't fall far enough to shatter, I call the Figure 7 Earth Movement a "Nontraditional Slump", i.e., it is still somewhat "coherent".
Figure 8.
Figure 9.
Figure 10.
Figure 11. Talus Cone, awaiting labeling for Educational Use.
[Editing currently in progress. More images planned, too.]
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