Final answer:
Tunnel gully erosion often occurs in soils with alternating layers of different permeability, which may be impacted by soil drainage, structure, and local vegetation. On Mars, these gullies suggest dynamic erosional processes that are very young and change with the martian seasons.
Step-by-step explanation:
Tunnel gully erosion is a type of severe land degradation that happens when water rapidly flows through subsurface soil paths, leading to the collapse of the surface soil and the creation of gullies. These events are usually associated with soil profiles that have alternating layers of different permeability, such as medium- to coarse-grained sand layers and silty clay layers. The conditions that promote tunnel gully erosion can be influenced by factors like soil drainage, soil structure, root structures, and local vegetation.
When looking at Mars' landscape, the gullies observed by the Mars Global Surveyor and the Mars Reconnaissance Orbiter indicate that there could be occasional flows of liquid water or transport of sediment, suggesting dynamic erosional processes. These gullies seem to be relatively young, as indicated by the lack of impact craters and their tendency to cut across recent wind-deposited dunes, complicating their direct comparison to specific Earth soil orders.