The Delaware Water GapWater gaps are a name for the geomorphological result of a river cutting throu

The Delaware Water GapWater gaps are a name for the geomorphological result of a river cutting through a mountain chain or ridge of rock, often because the stream already existed as tectonics made the rock rise and the water cut through as it rose. Here we have an iconic one from the Appalachians whose underlying rocks were first deposited some half a billion years ago. Over 100 million years two sedimentary stacks built up as mountains rose and were eroded twice, each starting with a basal conglomerate and shading upwards into deep marine (including turbidites deposited by continental slope landslides), sediments after the mountains had returned to dust. There is a major unconformity (called the Taconic) recording a long period of non deposition of sediments when the second mountain range rose and was eroded, with the next stack forming from the products of this erosion.The Ordovician Martinsburg Shale rose as a volcanic island arc collided with North America, followed by a ribbon of continent that gave us the subsequent folding and uplift and the Silurian Shawangunk conglomerate. All the while the Delaware River was eroding away through the resistant ridge forming quartzite (metamorphosed sandstone, tough and resistant to erosion) that had been cracked and shattered by the second collision, creating points of weakness in the first main ridge of the mountains that the river could exploit in its downwards rush towards the ocean. The area remains folded and faulted, testament to the last time it was tectonically active.The surface geology has been marked by several ice ages waxing and waning over the last couple of million years, and includes standard ice sculpted features and the resulting sediments left behind by several generations of glaciers and meltwater. There are several iconic waterfalls in the area, and the place was a centre of early tourism from the early 19th century CE and remains so today.Some 300 metres wide at the valley bottom, the river passes through a notch and past the deciduous forests that cover the modern hilly landscape, accompanied by a railway and interstate 80 clinging to the cliffs or bridging the gap. In both pre and post Columbian times the gap served as a corridor for humans, both Indians and pioneers, culminating in the 19th century creation of the road and railway.LozImage credit: 1: National Parks 2:Nicholashttp://bit.ly/2GqefsEhttp://bit.ly/2tJWaTMhttps://on.doi.gov/2tM9Yxjhttp://bit.ly/2FGLpmB -- source link

More pics about