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Hillock Geology
Courtesy of Professor Ray Weil, AGNR.
When these soils at the edge of the Hillock were disturbed by construction of the Comcast Center, massive erosion and flooding around the new buildings ensued.
The hillock is covered on its surface with a gravel deposit (called upland gravels by John Hack who mapped them). Most of these upland gravel deposits at Cherry hill (now cherry valley because of gravel mining) and other places have been mined out, so there are few remnants of this deposit and associated ecosystems left. Greenbelt National Park has a few hilltops with this deposit, but it was much more seriously affected by erosion. Our studies of erosion and runoff at Greenbelt Park indicate that these gravel topped hills are infiltration sites. Even during the highest intensity storms we do not see runoff from these sites. Water that infiltrates into these areas feeds the groundwater system.
Greenbelt park also shows how erosive these soils can be if overland flow (due to compaction, soil disturbance, or runoff from pavement) is directed onto them.
Hillock Soils
Courtesy of Professor Ray Weil, AGNR.
Sassafras pit on the shoulder of the Hillock.
The Sassafras soil exposed is a gravelly variant of the (as yet unofficial) State Soil of Maryland. It is an ideal teaching tool as it is highly typical of soils in the Ultisols soil order that is dominant in Maryland and Virginia. The only other relatively undisturbed soils I know if on campus are in the flood plain where any soil pit would be completely filled with water during much of the fall semester and all of the spring semester. The location of our Sassafras pit on the shoulder of the hillock slope has allowed us to build in a drainage system that keeps the pit dry enough for class use year-round. This is unique among the potential soil observation sites that I am aware of on or near campus.
Students at work in the soil pit.
The near surface O and A horizons (layers) of the Sassafras and related soils on the hillock, exhibit the effects of several centuries of forest vegetation and forest carbon and nutrient cycling. Here, students can also observe soil fauna and root-microbial interactions, first hand. The deeper horizons exhibit properties that reflect the longer term (millions of years) pedological and geological processes that shaped this area. These deeper features include clay accumulation, clay “skins” or cutans and well developed blocky structure in the B horizons. The prominent presence of rounded quartz gravels also bespeaks the former riverine history of the juncture between two of Maryland’s main physiographic regions, the Piedmont and the coastal plain.
The soil pit when drained.
For the past two years we have been monitoring the seasonal changes in soil water and temperature at several depths using sensors and an 8-channel datalogger. The resulting data and the opportunity to observe these parameter values on site in real time is another valuable aspect to this teaching facility. I have also used the hillock to train undergraduate and graduate students in making soil quality measurements as part of my collaboration with the U.S. National Park Service in monitoring the changing status of national park forest lands.