Explain why would the debris fan (mound of deposition) be greener than the surrounding areas? Think of the slide mass versus the surrounding in‐place bedrock in terms of porosity and permeability; how would these parameters differ?).
The debris fan, or mound of deposition, can appear greener than the surrounding areas due to differences in porosity and permeability between the slide mass and the in-place bedrock.
Porosity refers to the amount of empty space or voids within a substance, while permeability refers to its ability to allow fluids to flow through it. In the case of a debris fan, the slide mass typically consists of loose, unconsolidated materials such as soil, rocks, and vegetation that have been transported and deposited by gravity-driven processes like landslides or debris flows.
These loose materials tend to have higher porosity compared to the surrounding in-place bedrock. Higher porosity implies that there are more empty spaces, which can act as storage for water and nutrients. This increased storage capacity can support better vegetation growth, leading to a greener appearance.
Furthermore, the permeability of the slide mass is often higher than that of the in-place bedrock. High permeability means that fluids, including water, can easily flow through the material. As a result, the water from precipitation or underground sources can infiltrate the debris fan more easily, providing ample moisture for vegetation growth.
On the other hand, in-place bedrock is typically composed of solid and compacted rock, which generally has lower porosity and permeability compared to the loose materials of the slide mass. The lower porosity limits the storage of water and nutrients, while the lower permeability restricts the flow of fluids. As a result, the surrounding in-place bedrock may have less moisture available for vegetation, making it appear less green compared to the debris fan.
To investigate the differences in porosity and permeability between the debris fan and the surrounding in-place bedrock, you would need to conduct field surveys, collect samples, and perform laboratory tests. These tests can include porosity measurements using techniques like volume displacement or water saturation, as well as permeability assessments using methods like constant-head or falling-head permeameter tests. By comparing the results, you can quantify the variations in porosity and permeability and better understand their influence on the greener appearance of the debris fan.