Exercise 2: Mass Wasting
Mass wasting is a phenomenon that has resulted in over one million deaths and billions of dollars of damage in its recorded history. Mass wasting is classified by the rate at which debris moves down slope. For instance, rockfalls move at speeds of over thirty-MPH, while mudslides travel at around twenty MPH. This field trip explored two translational slides; one at the Gros Ventre River in Wyoming, and the other at the Madison River in Montana.
In Wyoming, the slide was caused by the clay and silt being saturated by rain and melt water, and occurred on a slip plane almost parallel with the slope. 40 million cubic meters of debris was moved and deposited almost 300 feet up the opposite slope. The debris caused a natural dam that created a lake, but the dam eventually failed, causing a nearby town to be nearly destroyed.
In Montana, the slide was triggered by an earthquake. As in Wyoming, the debris caused a natural dam, but the Army Corps of Engineers breached the dam to prevent failure. The rock that was displaced was mostly schist and gneiss, which is unstable.
The critical thinking section asked you to place a development. The northeast quadrant was the best because it had the proper amount of rainfall, a slope that was not too steep, and dense foliage. All of these are factors that help prevent landslides.
Exercise 9: Land Use
This fieldtrip takes us to the city of South San Francisco. This city has a diverse economy that includes tourism and technology. Also, the residential areas of town are separated from the commercial areas. There are also a good number of recreational and educational facilities in the city. As far as ethnic diversity, there are many types of ethnic groups spread throughout the city; there are really no ethnic boundaries as there are in bigger, older cities. There is a great deal of diversity in the physiography of the region. The eastern part of the city is made of filled land and subject to liquefaction. The western part of the city is quite hilly and poses a landslide threat. Both sections, however, are earthquake hazards.
Once again, in the critical thinking section you are asked if a development should be approved, based on landslide threat, earthquake threat, population density, and water supply. In this case the development should be denied due to the landslide threat of the area. There seems to be ample water supply, and the population density is not a problem as in many areas of California. Also, earthquake threat is not a serious concern in this region.