Mass movement hazards – reply post #2


Mass Movement is the movement in bulk of soil and rock debris down slopes in response to the pull of gravity, or could also be the result of gradual or rapid sinking of the Earth’s ground surface in a downward vertical direction. Mass movement is also known as mass wasting. This downward slope movement occurs by the force of gravity and does so without the aid of a transporting mechanism such as ice, water, or wind. Landslides are formed mostly of soil and/or rock, while snow avalanches are formed mostly on snow and/or ice. Landslides are categorized into two different categories: Rockfalls and Flows. Rockfalls typically occur in rock cut slopes when rock blocks become dislodged by weather, flowing water, or due to the surrounding rocks and soil being eroded. Because of the irregular, unpredictable nature of rock joints and weathering patterns, rockfalls cannot be precisely predicted (Robbins, 2021). Flows are when fluidized rock and soil fragments move in the form of a viscous mass. This happens when loose materials are saturated and behave as fluids rather than as solids. Tropical cities such as Hong Kong and Rio de Janeiro are susceptible to debris flows and landslides (Smith & Petley, 2013). These areas are densely populated increasing the risk of landslides on the deforested hillsides. Landslides may be caused by earthquakes or human behavior such as construction or excavation. Snow Avalanches occur with slopes ranging from 30-45 degrees and generally recur at the same spots, and so it is possible to detect future avalanches by recognizing avalanche paths. Mudslides develop when water rapidly accumulates in the ground and results in a surge of water-saturated rock, earth, and debris. Mudslides usually start on steep slopes and can be activated by natural disasters. Areas where wildfires or human modification of the land have destroyed vegetation on slopes are particularly vulnerable to landslides during and after heavy rains. These hazards are geographically indicative of the risks that the communities surrounding these locations might have to face, and possibly recurrently. Areas that are particularly mountainous with substantial snowfall may experience an avalanche if the conditions are right just like a community that has road construction going through mountainous areas with rocky edges (we’ve all driven through areas with signs that say “Watch Out For Falling Rock”) which indicates there is rock that may become dislodged and fall into the roadway, whether it be from weather or weakness in the rock surface such as the bedding or slip in the joint. Rain will play a major role in the majority of these mass movements from the landslides, mudslides, avalanches, to loosening of rocks in a rockfall. Areas that are more susceptible to rain are more likely to have these types of hazards than those that are in dryer climates, which would experience different types of hazards. I lived at the beach for many years and used to go surfing all the time so I watched out for hurricanes and such, so I used this website all the time to track them but I found a very good article on avalanches with some good information and some videos with some statistics as well for the States up until 2019. Hope you guys find it interesting (and helpful).



Robbins, B. A. (2021). Rockfall. Rockfall – an overview | ScienceDirect Topics. Encyclopedia of Geology. Retrieved October 14, 2021, from