Geomorphic characteristics of fens in the San Juan Mountains, Colorado
K. Jeon, J.R. Giardino, and B.K. M. Gonzalez


Fens are abundant in the formerly glaciated valleys of the San Juan Mountains, Colorado. Fens function as critical sedimentary sinks in alpine regions and record anthropogenic and natural phenomena that occurred in vicinity of the fens. For example, increased rates of sedimentation resulting from mining activity or forest fires can be identified. Whereas ecologists have contributed much in the study of fens, unfortunately, geomorphologists have almost ignored their study. Thus, no consistent classification systems of alpine fens based on geomorphology exists. We investigated geomorphic and sedimentary properties of alpine fens in the San Juan Mountains. Based on this, we developed a geomorphic classification scheme for fens, which consists of three classes: 1) valley-bottom, 2) valley-side, and 3) terrace. Morphometric measures of fen circularity and elongation were obtained for seventy fens. Valley-side fens are more elongated than either valley-bottom or terrace fens of similar elongation. Overall, the elongated fens have less circularity. Sediments were also sampled at the field sites. The sieved sediments yielded distinct mean phi values that conformed to the three categories. Coarse-grained particles were associated with valley-side fens, and medium-grained particles with valley-bottom and terrace fens, respectively. Thus, from a geomorphic perspective, our criteria of locational, morphometric, and grain-size analysis provide a consistent classification for alpine fens.


  1. Jeon, K.; Giardino, J.R.; Gonzalez, B.K. M., 2017, Geomorphic characteristics of fens in the San Juan Mountains, Colorado, in: The Geology of the Ouray-Silverton Area, Karlstrom, Karl E.; Gonzales, David A.; Zimmerer, Matthew J.; Heizler, Matthew; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 68th Field Conference, pp. 187-194.

More information...