Land slide is a form of ground movement where gravity is the primary driving force in the presence of other factors affecting slope stability. Slope stability is determined by shear strength vs. shear stress. Decrease in strength can be due to factors such as weathering, organic material and pore water pressure. Increase in shear stress can be due to loading, lateral pressure and transient forces. Rate of movement can be a slow creep in millimetres per year to fast in meters per second. The material sliding can be rock, sediment or soil. The material can slide, slump, flow or fall.
Triggering factors may be:
1.ground water (pore pressure),
2.absence of vertical vegetation,
3.soil structure,
4.erosion of the toe of the slope (undercutting), removal of slope base by a natural/man made process
5.weakening of the slope by water saturation from rain and snow melt, wetting and freezing, rain provides lubrication and increases mass
6. earthquakes, and volcanic eruptions.
Landslides are aggravated by human activities such as:
1. deforestation, cultivation, construction,
2. vibrations (traffic, machinery),
3. blasting
There are different types of land slides but we will focus on a specific landslide type occuring at this site called land slump. Here detached land blocks moved a short distances along a planar surface from a cliff like slope face called scarp. In some places it can form secondary slumps in a staircase pattern of displaced blocks.
To be able to log this cache as found you must email me answers to the following questions (do not post with your log):
1. What man-made structure is contributing to slope instability here? (Hint: see the list of triggering factors above)
2. What other triggering factors are contributing to the land slide (other than your answer to the first question).
3. If vibration is also a contributing factor here, what is the source of vibration?
4. In which compass direction did the slumps occur in this area?