Delaware Water Gap - Geology

Geology

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 it.

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

The mountains consist of Silurian Shawangunk conglomerate. This is gray quartzite, which makes the mountain highly resistant to weathering. The Silurian High Fall formation of sandstone is on the western side of the gap near the base. The eastern side of the Gap has the Ordovician Martinsburg shale. Sedimentary rock is along the river. The Bloomsburg Red Beds—a red shale—are at the Gap under Dunsfield Creek.

The Delaware Water Gap is about 300 meters across at river level and about 1400 meters wide at the top. The river through the gap is 283 feet above sea level. The ridge of the Appalachians that the Delaware crosses is called the Blue Mountains in Pennsylvania and the Kittatinny Ridge in New Jersey. This is the first major ridge of the Appalachian mountains. The New Jersey mountain is Mount Tammany;named after the Native American Chief Tamanend. The Pennsylvania mountain is Mount Minsi, named after the Native American Tribe of the area. The summit of Tammany is 1,540 ft (470 m) above sea level.

Dunfield Creek drains the Mountain and flows into the Delaware River. This creek flows over the Bloomsburg Red Beds of shale.

To the east of the Gap is the Great Kittatinny Valley which goes northeast along Kittatinny Mountain. The Paulinskill River drains the valley in this area.