Under what environmental conditions would you expect to find the thickest vadose zone?

• A. Forest
• B. Desert
• C. Submerged
• D. Tundra

Answer: (B)

The thickness of the vadose zone reflects how deep the groundwater table sits below the surface. It’s the unsaturated region from the land surface down to where groundwater begins. In climates with very little rainfall and high evaporation—desert conditions—the recharge of groundwater is minimal, so the water table stays deep. That pushes the boundary between the vadose zone and the saturated zone far down, producing the thickest vadose zone.

In a submerged environment, the pore spaces are saturated from the surface, so there isn’t a vadose zone to speak of. Forested areas and tundra generally have more recharge or different processes that keep the water table relatively closer to the surface, resulting in a thinner vadose zone.