Question

The fatal La Conchita landslide, discussed in this week's video, started moving like a landslide or slump, but then it began to flow more fluidly downslope. The geologic investigation showed that water and weak sedimentary rock were major contributing factors. Which of the following describes how water was able to mobilize this flow exceptionally rapidly? Select one: a. Water percolated the weak sedimentary bedrock via fractures and joints b. Days of heavy rain saturated the landslide material so it flowed down slope like mud c. Groundwater in the landslide pooled up on a buried fault surface, which consisted of impermeable clay (i.e., fault gouge) and increased the pore pressure d. A recent wildfire in the area destabilized the topsoil and made the slope vulnerable to erosion. e. All of these

Answer 1

b. Days of heavy rain saturated the landslide material so it flowed down slope like mud

Step-by-step explanation:

In 1994, La Conchita experienced a landslide as a result of water infiltration through multiple open cracks which had opened on the hillside and surface runoff was infiltrating into the subsurface this resulted in the landslide slumped as a coherent mass of material.

in 2005, the results of the 1994 landslide contributed to the 2005 landslide. Before the La Conchita landslide occurred, the area experienced two weeks of heavy rainfall. It was estimated that the new rainfall did not enter the deposits left behind after the 1995 landslide, but slid off it taking surface debris and few new materials with it resulting in a shallow and rapid fluid flow