APPALACHIAN TRAIL: TECTONICS AND GEO-POETRY (Invited Presentation)

For a century the national parks have been among our most treasured collective possessions, not only for outdoor enjoyment but also as places for deeper understanding of human events in relation to those of Nature. In a few locations this almost transcendental experience includes the fourth dimension of geologic time, nowhere more evident than the Grand Canyon. Its Trail of Time enhances that understanding with human footsteps as proxies for the magnitude of time while boulder samples of distant outcrops bring visitors face to face with an older, more complex world than most can imagine, their exposure to tectonic “geo-poetry” of Harry Hess’s classic History of Ocean Basins.

The Appalachian Trail along the backbone of one of the world’s great mountain systems has similar possibilities but unless placed clearly in geology’s vast expanse of time and change its outcrops are unlikely to stir public souls. Geology as a discipline conveys that awe of time rather poorly. Perhaps a human tectonic time scale would help, the basic unit as fingernail growth distance in km or miles ( 1 m.y. = ~ 25 FGK or ~ 15 FGM). The Appalachians formed by overlap of several mountain systems, each mashed and welded a bygone ocean's contents onto N America's edge. Collision of Africa, ~ 3750 -5000 FGM ago, detached great slabs of that margin and pushed them 100 - 200 km onto the continent, a tectonic bulldozer that plowed foreland debris as the Valley and Ridge's spectacular folds. For much of its length, the AT winds back and forth along that Great Valley tectonic boundary before turning east across the old continental margin to pass through cooked remnants of a vast former ocean. The NPS could do much more to convey and display the AT's potential geo-poetry: simplified tectonic descriptions, more signs at significant tectonic boundaries, clearing of “green tunnels” for better viewscapes, all to help the AT public join Playfair and grow giddy by looking “so deeply into the abyss of time.”