Delaware Water Gap

en.wikipedia.org/wiki/Delaware_Water_Gap

A water gap is a geological feature where a river cuts through a mountain ridge. The Delaware Water Gap began to form 450 million years ago when quartz pebbles were deposited in a shallow sea, on top of the Ordovician Martinsburg shale. The Martinsburg Shale was uplifted when a chain of volcanic islands collided with North America around the same time. These islands went over the North American plate, and deposited rock on top of plate, forming the Highlands and Kittatinny Valley.

Then around 400 million years ago, a small, narrow continent collided with North America. Pressure from the collision twisted the Silurian Shawangunk Conglomerate, shattering the gray quartzite as it was uplifted. In addition, the pressure created heat, melted the quartzite, and allowed it to bind the quartz pebbles and conglomerate together. This layer was then uplifted, and the Delaware River slowly cut its path down through the shattered quartzite. If the quartzite had not been cracked, the river may not have been able to cut its path through the mountain.

Millions of years of rain, ice, snow and wind erosion shaped the area. The Wisconsin glaciation, which occurred between 21,000 B.C. to 13,000 B.C., covered the entire Kittatinny Ridge and ended near Belvidere.When the glaciers retreated, the gap assumed its present form.