A RE-INTERPRETATION OF WATCHUNG MOUNTAIN WIND AND WATER GAPS, NORTHERN NEW JERSEY

The Watchung basalt ridges of northern New Jersey resemble, in miniature, the Appalachian Ridge and Valley system to the west. In the Watchungs, as in the Appalachians, dry wind gaps and under-fit water gaps punctuate resistant ridges. Pioneers in geomorphology such as Davis and Johnson interpreted wind and water gaps in the Watchungs as similar to those of the Appalachians, developing from superposed drainage and stream capture. These early geomorphologists worked without knowledge of tectonic theory and endogenic factors that control landscape development. Modern interpretations of the Appalachian drainage landscape now incorporate westward migration of the East Coast drainage divide from the opening Atlantic basin to account for stream reversals and channel abandonment.

Geomorphic research in the Watchungs has declined since the advent of modern process theory. The geomorphology of the Watchung ridge system is due for an update. We found that structural relationships are probably much more significant than previously realized, and we propose that pro-glacial erosion may have played a significant role in developing the wind and water gap passages. Single faults or fault systems accompany most of the ridge gaps. Previous researchers identified similar structural relationships in the Appalachians, for instance, in the Delaware and Lehigh valleys. The weakened rock would be susceptible to erosion. Furthermore, erosion that developed the gaps may have occurred much more recently than Davis or Johnson supposed. The Watchung ridges were at some points completely over-run by glaciers, and acted to dam the Passaic and Rahway rivers to form glacial Lake Passaic. Gradual or catastrophic glacial lake drainage may have played a role in developing or expanding existing passages through the ridges. Direct evidence for this is difficult to find in the mostly-urbanized land surrounding the mountains.