One of the most common geomorphic hazards is Landslides. In the majority of cases, landslides are caused by excessive rainfall. This rainfall saturates the surrounding terrain, increasing the weight acting on a particular part of a hill. It then becomes too weak to support its own weight. The result is a landslide, where a whole area of rock and materials falls down one side of the hill, leaving behind it, a trail of destruction.
LANDSLIDE, THE MAMAYES, PUERTO RICO
In October 1985, a landslide destroyed 120 houses and killed at least 129 people-the greatest number of casualties from any single landslide in North America. The catastrophic block slide was triggered by a tropical storm that produced particularly heavy rainfall
Like many other landslides, this one in the Mamayes, Puerto Rico was triggered by a natural disaster. The very heavy rainfall that triggered the landslide was result of a tropical storm that passed over the area. The soil in this densely populated area could not withstand the increased ground saturation and collapsed.
ROCK SLIDE, FRANK, ALBERTA, 1903
1. When did the Frank Slide take place?
On April 29, 1903 at 4:10 AM, 30 million cubic meters (90 million tons, 82 million tonnes) of limestone fell from Turtle Mountain in just 90 seconds.
2. What caused the Frank Slide?
Secondary causes were coal mining inside the mountain and weathering.
3. How many people were killed?
Of the 600 people living in Frank at the time of the rockslide, approximately 70 were killed.
4. What was destroyed in the slide?
There were 7 miner's cottages (6 with people in them) destroyed, a dairy farm, ranch, shoe store, livery stable, cemetery, 2 km of the road and CPR rail line, 3 km of the Frank and Grassy Mountain Railway, a construction camp and all of the surface buildings for the Frank mine.
Avalanches occur in mountainous areas all over the world. They occur when a slab of snow is worked loose and slides down a mountain. Although, in many incidences, the weight of a person on the snow can cause a slab of snow to break away and start an avalanche, they also frequently start without any human intervention. Wind is the most common cause of avalanches. Wind can deposit snow 10 times faster than snow falling from storms. Wind erodes snow from the upwind side and deposits snow on the downwind (lee sides)." This is called "wind loading".
The added weight from snowstorms also causes avalanches. If the weight of new snow is added faster than the buried weak-layer can adjust to its load, then it fractures and forms an avalanche. Quick warming or rapid melting of snow can also cause avalanches. For example, rain on new snow almost instantly causes avalanches. Strong sun or warm temperatures can also cause rapid melting of the snow and creates wet avalanches.
Rock and snow avalanche, Mount Huascaran, Peru. In 1970, a rock and snow avalanche caused by an earthquake on Mt. Huascaran, Peru, buried the towns of Yungay and Ranrahirca. The death toll from the Debris Avalanche was 18,000 (total fatalities from the earthquake and the debris flow was 66,000). The avalanche started as a sliding mass of glacial ice and rock about 3,000 feet wide and one mile long. The avalanche travelled about 11 miles to the village of Yungay at an average speed of more that 100 miles an hour. The fast-moving mass picked up glacial deposits and by the time it reached Yungay, it is roughly had about 80 million cubic yards of water, mud, and rocks.
How do landslides affect us?
Landslides cause property damage, injury and death and critically affect a variety of resources. For example, water supplies, fisheries, sewage disposal systems, forests, dams and roadways can be affected for years after a slide event.
The negative economic effects of landslides include the cost to repair structures, loss of property value, disruption of transportation routes, medical costs in the event of injury, and indirect costs such as lost timber and lost fish stocks. Which could then affect the local economy and quality of life as landslides can affect water availability, quantity and quality.
With the case studies I have discussed and presented in this essay, and the contrasts of such geomorphic hazards, you can conclude that mass movement processes is one of the most costly and deadly of all hazards as the speed of the landslides is so high that reaction times are very small, meaning higher death rates. With examples from LEDCs and MEDCs, the differences that are apparent are, that many areas in LEDCs are over-crowded and the poor housing and conditions do not help. For example with the Mamayes, Puerto Rico incident, the poor sewage services meant that raw sewage was pumped onto the mountainside, increasing the saturation of the soils etc. One other factor we must consider is the amount and accessibility to modern technology, which aids in increasing the reaction time, ultimately leading to a lower death and damage rate.
