We have been exploring the geology along the Wall of Manitou — the Catskill Front. From time to time we encounter bouquets of wilted flowers lying near the top of a Catskills Waterfall. These are most commonly found near the tops of Kaaterskill or Plattekill Falls. We found one again, at Plattekill, during our most recent visit. They are, we sadly suppose, the poignant reminders of loved ones who fell to their deaths at those falls. Our Catskills waterfalls are beautiful sights to see, but they draw people too close to the edge. A split second of uncertainty or carelessness and someone loses their life. It is tragic; it happens.
But, to geologists, there is a simple question. How did these waterfalls, with their hazards, come into existence? Haven’t waterfalls just always been there? Well no they haven’t; they were brought into existence by geological processes. We just have to be observant enough to figure out those processes.
Most waterfalls reflect the presence of something called cap rock. That is a horizon of very resistant bedrock found at the very top of the falls. That horizon of rock holds up well against the processes of weathering and erosion and it forms a table over which the water will fall. That explanation is most widely known for Niagara Falls. Most people, somewhere along the line, learn that the top of Niagara is composed of tough rock, a massive horizon of limestone that has long supported the falls. That is the case with Kaaterskill Falls; it too has a cap of very resistant rock; this time it is sandstone. That ledge was featured as a roof in a well-known Winslow Homer picture.
But there may be more to it. We have visited Plattekill Falls and have seen something else. Take a look at our second photograph. You will see a very convincing example of a cliff. Look at its smooth walls. This cliff actually lies at the edge of what is called the “Devil’s Kitchen” and it is just a little bit above Plattekill Falls. It lies just adjacent to Bridal Veil Falls. It deserves attention. It may tell us a lot about waterfalls in the Catskills and the origins of our region’s cliffs as well.
We recognized this cliff for what it was right away. Geologists call such a smooth vertical wall a “joint.” A joint is a major fracture in the rock. It is similar to the more widely known geological fault, but there is a big difference. A fault is a fracture, along which there has been motion. We call such motions earthquakes and they are just that. They shake or quake the ground at the moment they occur. A joint is different; it does not involve any motion. If you had been there when the Plattekill Falls joint snapped then you would hear a very loud cracking sound, but — then it would be all over. There would be no motion; houses would not fall down; people would not die. You might find yourself asking for a refund!
Well, actually not everything would be entirely over. That joint would lie there and be a plane of weakness in the bedrock. Eventually, and it would likely take centuries or millennia — or even a lot longer, something would happen. A glacier might come by and yank the lose rock out of the ground, leaving that sort of joint wall behind. Millennia of weathering and erosion might accomplish something similar and that wall of rock would come tumbling down. We are guessing that this Devil’s Kitchen wall was formed due to local events. If you have ever been there, then you know that powerful streams rush through there at rainy times of the year. We are guessing that stream erosion undermined this wall and it formed when adjacent bedrock tumbled down. In the end, we think that both Plattekill and Bridal Veil Falls began as joints — as did so many other falls in the Catskills.
We measured the compass direction of our Devil’s Kitchen joint and found it to be south-40-degrees west, almost perfectly southwest. That did not surprise us; we expected it. Starting about 300 million years ago there was a great plate tectonic collision in this part of the world. Something you would call Africa began colliding with North America. It approached from the southeast, so the compression was along a northeast to southwest line. That compression helped create our joint and many others throughout our region.
We have begun to perceive a complex chain of events. Hundreds of millions of years ago Africa collided with North America. Bedrock was compressed and joints formed. They lay there and did nothing for all that time. But, in recent millennia, processes of weathering and erosion, probably hastened by the Ice Age, accelerated changes. Joints were gradually turned into waterfalls and cliffs. When people came along, some of them fell to their deaths. Those geological processes created our scenic waterfalls, sometimes irresistible, but also dangerous attractions.
Be careful out there!