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Harbor To Lead Brushy Hills Walk Saturday
At the Brushy Hills Preserve this Saturday morning, March 9, from 10 to noon, David Harbor, a professor of Earth and Environmental Geoscience at Washington and Lee University, will lead a walk entitled “Landscape Shaped by Water.”
The walk will focus on weathering and erosion features in the Preserve, including changes wrought by water over both geologic and more recent times.
“Brushy Hills is a great example of the Great Valley carbonate uplands (as opposed to, for example, a river bottom) with its residual soils, deep weathering and hillslope erosion,” said Harbor, a geomorphologist who has studied how rivers erode mountains over tens of millions of years, as well as during floods in the blink of an eye.
“Dissolution of the underlying carbonates leads to prominent sinkholes, as well as angular clasts of insoluble chert, largely from the Beekmantown Formation,” he continued. “Furthermore, stream erosion and deposition are still recovering from the disturbance caused by former land use.”
The walk will begin at the springhouse trailhead, on the Up and Over trail, where Harbor will point out some dramatic limestone outcrops revealed along the former roadbed. Walkers will then continue onto Ol’ Yeller, where the group will explore a line of four ancient sinkholes, and then to the Tanager and Middle Way trails, where recent collapse has created a couple of steep-sided sinkholes near the valley bottom.
Sinkholes are typical of karst topography, Harbor said, noting that the word “karst” comes to us from scientists in Eastern Europe, where limestone formations are widespread. Karst is also common in the Great Valley of Virginia and a few other parts of the Appalachians as well, he said, where just onefifth of rock material traveling downstream is sediment, with the rest being chemically dissolved rock.
Finally, on the return down Tanager, walkers will find an old stream bed with valley floor fans and gullies, the result of 19th century human agriculture and habitation. “So we can see in this valley the response to changes by human hands,” Harbor observed. He noted that while indigenous peoples also affected the land, by the late 1800s the land was much more hard-used.
Walkers are encouraged to wear footwear appropriate for rough woodland trails.
This is the 25th year of Preserve advocacy and events sponsored by the Friends of Brushy Hills.
Rain date for the geology walk is the following Saturday, March 16. For weatherrelated and other questions, contact friendsofbrushyhills@ gmail.com. For directions to the Preserve and a trail map, visit www.friendsofbrushyhills. org.
