A soil sequence including silt gravel, gravel-sand-silt, silt sand, sand, silt, peat, muck and swamp has what depth?

A soil sequence including silt gravel, gravel-sand-silt, silt sand, sand, silt, peat, muck and swamp has what depth?

• A. 1 ft
• B. 2 ft
• C. 3 ft
• D. 5 ft

Answer: (C)

Understanding how a soil profile is read helps with this question. A soil sequence lists horizons from the surface down to a bottom boundary, and the depth is how far you can see all those horizons in the vertical column. Here, the profile includes eight horizons in order—from silt gravel through peat, muck, and swamp. Peat, muck, and swamp are organic layers that commonly sit near the surface, so all of these horizons can fit within a shallow depth of about three feet. If you tried to push the depth to one or two feet, you wouldn’t reasonably accommodate all the horizons shown; going to five feet would imply additional layers beyond what’s listed. Hence the depth corresponding to this sequence is 3 feet.

Understanding how a soil profile is read helps with this question. A soil sequence lists horizons from the surface down to a bottom boundary, and the depth is how far you can see all those horizons in the vertical column. Here, the profile includes eight horizons in order—from silt gravel through peat, muck, and swamp. Peat, muck, and swamp are organic layers that commonly sit near the surface, so all of these horizons can fit within a shallow depth of about three feet. If you tried to push the depth to one or two feet, you wouldn’t reasonably accommodate all the horizons shown; going to five feet would imply additional layers beyond what’s listed. Hence the depth corresponding to this sequence is 3 feet.