The ‘blue’ in the Blue Ridge Mountains
Hue never ceases to fascinate, but will it last?
The Blue Ridge Mountains are every shade of green these waning days of May, what with all the rain of late in Rappahannock County. But it won’t be long until the sultry dog days of summer arrive, and with them the distinctive blue haze that gives these ancient mountains their famous name.
The “blue” one often sees when beholding Rappahannock County’s splendid backdrop can be attributed in scientific part to the summer heat. In short, the mountain trees, particularly oaks, emit hydrocarbons— isoprene, specifically — during the hottest days of summer as a means of protection from the sun’s scorching rays.
“The bluish color of the mountains from a distance is produced as a result of the selective scattering of light in the atmosphere by tiny particles produced by a chemical reaction between hydrocarbon molecules released by vegetation and ozone,” Edgar W. Spencer, professor emeritus of Geology at Washington
& Lee University, educates in his 2017 Guide to the Geology and Natural History of the Blue Ridge Mountains.
When considering the captivating hue, observers often recall one of the earliest descriptions by Blue Ridge admirer Thomas Jefferson, whose Monticello home provided a constant view of the ever-changing mountains.
“The rapture of the spectator is really indescribable,” Jefferson wrote.
But it was actually the Cherokee Indians who christened the mountains “blue.”
“Humans arrived in the Blue Ridge perhaps as early as 12,000 years ago,” observes Friends of the Blue Ridge Mountains, a conservation group that works to protect the mountains from development and environmental deterioration.
“The Siouan Manhoacs, Iroquois, and Shawnee all hunted and fished the Blue Ridge in Virginia, and the Cherokee lived in the Blue Ridge,” the group observes. “Cherokee holy people have reported that when Andrew Jackson burned Cherokee villages and marched the inhabitants off to Oklahoma, Cherokee medicine people fled up into the Virginia Blue Ridge.”
Apart from their distinct color, the age and former height of the Blue Ridge Mountains have also fascinated observers.
“What we see today,” Spencer writes, “are the remains of mountains that may have been as high as the Alps or the Himalayas (20-40,000 ft.) when they were forming. Over the last 200 million years erosion has reduced the height . . . of what had once been high and rugged mountains.”
“At the time of their emergence, the Blue Ridge was among the highest mountains in the world,” the Friends add. “Today, as a result of age and erosion, the highest peak in the system, Mount Mitchell in North Carolina, is only 6,684 feet high — still the highest peak east of the Rockies.”
The highest point in Shenandoah National Park, comparably, is the summit of Hawksbill Mountain, with an elevation of 4,050 feet.
As mentioned, time and erosion have taken their toll on the Blue Ridge, although in a human’s span of life they’re not shrinking very fast.
“As best as we can figure our summits are coming down 30 feet per million years, which is pretty slow in the scheme of things,” William and Mary Professor of Geology (and Geomorphology) Gregory S. Hancock told this newspaper while he and his students took “rock weathering” measurements in and around Sperryville.
More intriguing, the Blue Ridge chain we see today — their oldest rocks 1.3 billion years old — replaced mountains that stood here before.
“The Blue Ridge contains a fascinating record of multiple mountain building episodes,” Spencer points out, “separated by periods during which mountains formed earlier were eroded away and seas advanced across the region before renewed mountain building took place.”
As for Shenandoah Park, Spencer describes it as “one of the most intensively studied sections of the Blue Ridge. It’s ecology and geology continue to be carefully examined by many scientists . . . Except for acid rain and the construction of road and tourist facilities, the environment in the park has been little disturbed by humans since 1935.”
Then again, destructive gypsy moth caterpillars are picking up where humans left off, defoliating numerous trees in the park, especially the biggest hydrocarbon emitting trees of all — the oaks.
In 1940, the Blue Ridge guide reveals, 72 percent of the trees in Shenandoah Park were chestnut oaks and northern red oaks. Today, oaks account for less than 60 percent of the park’s forest, their number continuing to fall.
Keep losing the oaks, in other words, and the “blue” could one disappear from the Blue Ridge Mountains.