To know how the U.S. national capital area was created geographically — the basic structures formed by millions of years of Earth’s dynamics — is to better understand not only why certain species of plants and animals flourish there, but also why they (and Washington. D.C.) are there at all.
Ford Cochran, a professor of geology and environmental science, is Director of Programming for National Geographic Expeditions — and a professor for National Geographic Great Courses. In celebration of the 100th anniversary of the National Park Service, he produced Wonders of the National Parks: A Geology of North America, a Great Courses series of 36 digital lectures about the titanic forces that shaped America’s parks.
In this interview, Cochran describes the fundamental geology underlying the 2016 National Parks BioBlitz in the Washington, D.C. area.
There are BioBlitzes all over the country today, but focusing on the National Capital Area to begin with, what should we understand about the way this area has been uniquely formed physically, and how does that in turn shape the biodiversity we are are celebrating?
It’s no accident that the National Capital Area Bioblitz is in a place where it is. It’s because it’s no accident that the great urban center of Washington is where it is. It’s one of many cities in the eastern United States that lies on the Atlantic seaboard fall line, which to geologists is an incredibly important boundary.
The fall line set the course of history for our country. It is the place that defines the upward limit of navigation on many rivers in the eastern United States. On one side of the line is the Atlantic coastal plain, a place where you have all sorts of relatively recent sediments that have been shed off the mountains to the west, the Appalachians, and even the predecessors to those mountains which had risen there. On the other side of the line, to the west, is the Piedmont. The line runs right through these two provinces, and the place where they come into contact together runs right through Washington, D.C.
What does that mean to someone on the ground here in D.C.? When you are looking around, what do you see?
Visually, it means that if you go to say Georgetown, to Key Bridge, or if you go to a place like Roosevelt Island, you will see on one side, the eastern side, relatively flat landscape. These eastern landscapes are underlined by lots of sediments, material that came from elsewhere — the material that was shed and carried by streams and deposited where it now lies. This happens often in flood events, when the Potomac River overflows its banks.
But if you look upstream, what you see is rocks in the Potomac River. And just a few miles upstream from Roosevelt Island is another part of the National Park Service, Great Falls Park and Mather’s Gorge, named for Stephen Mather, the first director of the National Park Service. What you will see there are rocks full of sparkling crystals — metamorphic rocks, as opposed to sedimentary rocks.
These are really ancient rocks. They have a tremendous history. They are the roots of mountains that were formed when Pangea, the supercontinent, was created, and even pre-date the formation of that supercontinent.
These are rocks that were buried miles deep in the Earth’s crust under tremendous pressures and elevated temperatures and the minerals within them crystallized. They were subjected to conditions unlike those at the surface of the Earth, so they are entirely different.
So upstream you see lots of this hard bedrock, but as you travel to the east you are going to see lots and lots of relatively flat, gently rolling landscapes, underlaid by what ultimately becomes well over a mile — nearly 8,000 feet –of sediment in a thickening wedge that travels right to the Atlantic Ocean, and continues offshore to the continental shelf and down the continental slope.
It is dramatic to look at from a geological point of view, and certainly it is spectacular scenery, but I imagine lots of niches have been created in this landscape for different plant species, and the animals that feed off those plants.
Absolutely. Soils are the consequence of the bedrock below and the sediments from which they are derived. Soil is tremendously important in determining what sort of plants are going to grow.
How much sunlight a location gets is determined in part by what the land is doing: a relatively flat land can host forests where the canopy is subjected to full sunlight. But you go to Rock Creek Park, in the nation’s capital, where we hosted our first BioBlitz ten years ago in partnership with the National Park Service, and you see the deep channels, the stream valleys that Rock Creek has cut for itself through the rocks. This is a place that has shaded banks which are home to a different set of plants and animals.
You have explored many of the parks in in the greater Washington, D.C., area. What are some of your favorite spots?
I love the banks of the Potomac River because it is where the land comes into contact with water and where you can see so much. If you make your way from the banks into the forest, sometimes the woods open up a little bit, and you may find shaded streams. There you see not only people enjoying themselves, including many in sporting activities on the river, but on a day when the water is clear you may see fish and all the other wonderful aquatic life, like insects on the surface. It’s a wonderful place to see so many distinct habitats in one outing.
A lot of animals move through our area, especially migrants such as the wonderful songbirds that stop over on their long hauls north ad then back south. There is a lot of refuge for them in the Washington wilderness, places to rest and be nourished.
That’s right. There is so much water. Not just the rivers and ponds, but also swampy grounds and coastal plains. Washington was known as “Foggy Bottom,” a swamp that was here on the coastal plain, where the Potomac would overflow its banks, accumulate and pool over sediment where trees wouldn’t grow. That water is great for migratory birds, and still today these are incredibly important locations for our birds that migrate through the capital area.
It’s a really wonderful city for people to live in, because it has so much green space, but also because it also has so much blue space, so much water.
You recently produced Wonders of the National Parks: A Geology of North America, a series of 36 of your lectures on DVD and for video download, published by Great Courses and National Geographic. Your explanation of the geology underlying the National Parks BioBlitz in the Washington area tempts me to ask for an overview of the geology of some other iconic parks.
One of the marvelous things about visiting National Parks all across the country, including those in Washington, D.C., is that many of them were set aside originally to preserve marvelous landscapes. When you see a dramatic landscape, typically what that landscape reflects is the drama of its own creation.
There are fantastic stories embedded in the places that we visit. Washington, D.C. is where it is because there is this incredible story of ancient mountains and the ripping apart of the continents to form the basin that is now filled by the Atlantic Ocean. Much of that story is now preserved in and around Washington, in the places that people will visit on the BioBlitz, like many of the parks that are also hosting BioBlitz events this weekend.
In our parks are stories of volcanism, stories of glaciers, of vast caverns formed underground. They really reflect the long history of the North American continent and of our planet. So it was a real treat for me as a person who loves geology, and who loves the beautiful, beautiful landscapes, and the wildlife, of our parks, to have the opportunity to dwell on them long enough to put together 36 lectures about them.
There are more than 400 units in the National Park Service, so wherever you live in the U.S., you are never far from a National Park. Use this centennial year of the National Park Service and, like we are all being urged to do, Find Your Park. And if you can, find a BioBlitz as well. They are happening all over the country. There is probably a BioBlitz near you.
Thousands of people are participating in a nationwide series of BioBlitzes this weekend, celebrating the centenary of the U.S. National Park Service. BioBlitzes also celebrate America’s natural heritage through scientific explorations and cultural events in the national parks. Washington, D.C., home to several parks within and around the city, is at the center of all this activity.
David Braun is director of outreach with the digital and social media team illuminating the National Geographic Society’s explorer, science, and education programs.
He edits National Geographic Voices, hosting a global discussion on issues resonating with the Society’s mission and major initiatives. Contributors include grantees and Society partners, as well as universities, foundations, interest groups, and individuals dedicated to a sustainable world. More than 50,000 readers have participated in 10,000 conversations.
Braun also directs the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship.