2004 Japanese Landslide Video 1. What are the factors that contributed to the la
ID: 294675 • Letter: 2
Question
2004 Japanese Landslide Video
1. What are the factors that contributed to the large number of mass movement events shown in the video? How did weather, topography, tectonics, and development influence the two specific events shown at 0:25 and 0:55 minutes in the video?
2. What can be done to repair the damage and prevent future mass wasting events in the two examples shown?
3. What observations can you make about the character of the mass movements at 0:25 and 0.55 minutes in the video? Did the material move as a semi-coherent block or as a chaotic fluid? What is your evidence?
Explanation / Answer
1) The main factors that contribute for mass movement are gravity and steepness of slope. There are several factors like composition of slope material, Weight and Friction of Slope, Regional Climate Conditions, Water Content within Slopes & Gravity that influence mass wasting, but ultimately it is a battle between friction and gravity.
At 0:25 minutes:
The amount of water in the soil is a major factor in the stability of a slope. Little water can prevent slopes from sliding due to surface tension but too much water lubricates the individual grains of sediment decreasing friction between each grain, so the possibility of mass wasting increases. The increase of water within the soils due to rain was the clear reason of debris flow at 0:25 minutes.Slope material that becomes saturated with water may develop into a debris flow or mud flow. This flow of mud was initiated by slope movement. Since the slope was not too steep so the debris flow was relatively slow. Also the construction add & helps to build weight on slope so that debris can slide easier.
At 0:55 minutes:
This case was also initiated by the heavy rainfall activity but it is little different from the previous one as in this case the angle of repose or we can say the slope was very steep. The combination of small movements of soil or rock in different directions over time directed by gravity gradually tend to downslope. The creep & velocity of the material is proportional to the steep of the slope. The creep makes trees and shrubs curve to maintain their perpendicularity, and they can trigger landslides if they lose their root footing.
2) Proper designing during construction projects can help to eliminate increased mass wasting. Human activities which can promote mass wasting such as undercutting the base of the slope, adding weight to the upper part of the slope by building large structures, removing vegetation, and saturating the ground with water increase the risks of mass wasting. Nowadays, there are various geotechnical solutions also availablethat include barriers and retaining walls, drainage pipes, terracing the slope to reduce the steepness of the cuts, and immediate revegetation.
3) The road was buckling at 0:25 minutes & coherent block moved at 0:55 minutes. The material was a type of chaotic fluid at 0:25 minutes & it was like semi-coherent block at 0:55 minutes.
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