THE FALLING SPRING OF VIRGINIA

The most pronounced thermal spring area in the eastern U.S. is centered in western Virginia, and extends into adjacent West Virginia, Maryland and Pennsylvania. The highest temperature springs within this area emanate from Ordovician limestones exposed in the Warm Springs anticline. The Warm Springs anticline is within 20 km of an Eocene dike swarm. There are several theories that explain the source of the heat in the springs.

The Falling Spring presents an interesting interplay between physical, chemical and biologic processes. Separate warm and cold water seeps occur in Warm River cave and mix before surfacing as the Falling Spring. Spring water mixes with runoff before cascading over Falling Spring Falls, a waterfall that is at least partially man-made by surface mining of travertine. The travertine is primarily a cascade deposit formed during a time when the waterfall was at a higher topographic position, possibly during the beginning of the present erosion cycle. Today, travertine forms preferentially at the base of the waterfall, apparently due to CO2 degassing in the cascade. Formation of the travertine is further catalyzed by bryophytes and algae.

The undercut cliff below the waterfall creates a sheltered surface that is not inundated by direct surficial flow of the spring, but is indirectly hydrated by spray from the waterfall. This moist microhabitat is designated as a spray cliff community. These community types are often species-rich and may support up to 268 bryophyte species, 14 of which are dominant in the Falling Springs spray cliff: Anomodon rostratus, Brachythecium rutabulum, Brachythecium salebrosum, Bryum pseudotriquetrum, Cratoneuron filicinum, Didymodon tophaceus, Gymnostomum aeruginosum, Hygroamblystegium fluviatile, Hygroamblystegium tenax, Hymenostylium recurvirostre, Hypnum lindbergii, Marchantia polymorpha, Philonotis muhlenbergii, and Plagiomnium ellipticum. Spray cliff communities on limestone in Virginia are considered rare.