How the Susquehanna River and the Chesapeake Bay were formed

The Susquehanna River river drops 1,191 feet during its journey from Cooperstown, New York, to the Chesapeake Bay. It has seen many changes in the landscape through which it flows over the past 325 million years.



a large body of water with a mountain in the background: The Susquehanna River as seen from the Breezyview Overlook north of Columbia. Accomac Point is on the left side.


© Submitted
The Susquehanna River as seen from the Breezyview Overlook north of Columbia. Accomac Point is on the left side.

Today, the Susquehanna River is considered one of the oldest rivers in the United States — if not the oldest. The river flows over rocks that are younger than itself — and that is unique.

Loading...

Load Error

Rewind the earth’s geologic video to at least 325 million years ago. In the vicinity of Baltimore, Maryland, and Wilmington, Delaware, there were the Taconic Mountains, formed from an island arc collision some 425 million years ago. The Appalachian Mountains did not yet exist. An ocean occupied the area where that mountain range is located today. Although the Taconic Mountains have eroded, the river was flowing in the opposite direction of today, creating its early channel.

Start the day smarter. Get all the news you need in your inbox each morning.

Pangea

Fast forward to 300 million years ago, and a huge collision between Africa and North America occurred to help in forming the supercontinent Pangaea. This collision is known to geologists as the Alleghanian Orogeny, which seriously deformed our crust into a series of folds and broken pieces of crust containing faults. The Appalachian Mountains were pushed up during this episode, which lasted about 20 million years. The Appalachian Mountains were once as high as the present-day Rockies. Now, with the Appalachian Mountains the high point, the Susquehanna River reversed its course and flowed in a southeastern direction.

Geology’s role in flooding, mining: Jeri Jones, Pivotal Moments in York County History

UP NEXT

UP NEXT

For the next 150 million years, the constant downward erosion of the river cut into the crust, establishing its channel and claiming its real estate.

About 200 million years ago, Pangaea was well underway to splitting apart into the world we know today.  This series of rifts did not play a big role in the life of the Susquehanna. The river was flowing through a relatively flat plain as the crust would either go with Africa or stay with North America.



a man sitting on a rock: Example of a pothole in diabase north of the Falmouth Boat Launch and south of Three Mile Island. Roxann Barnett for scale.


© Submitted
Example of a pothole in diabase north of the Falmouth Boat Launch and south of Three Mile Island. Roxann Barnett for scale.

Meteor helped form bay

Advancing the video ahead to post Pangaea, severe weathering and erosion worked on the landscape, and the Susquehanna River carried much sediment downslope onto a continental shelf of the newly born North America. Some researchers suggest that some 4 to 5 miles of the crust were removed from over our heads by these processes with assistance by the river.

About 35.5 million years ago, our area was greeted with an extraterrestrial visitor.  An asteroid or meteor collided with Earth in what is today the southern portion of the Chesapeake Bay. Traveling at about 144,000 miles per hour, the object created a 25-mile wide crater a half mile deep. This event was the first step in creating the Chesapeake Bay. The Chesapeake Bay Impact is one of the best-preserved craters in the world, although today sediments have slumped into the large depression.



a rocky island in the middle of a body of water: “The Deeps” river channel below the Holtwood Dam on the Susquehanna River. The river is about 100 feet deep in this area.


© Submitted
“The Deeps” river channel below the Holtwood Dam on the Susquehanna River. The river is about 100 feet deep in this area.

Ice age

The final chapter of this story involves Pennsylvania’s last geologic event known as the Ice Age. From at least 770,000 to 17,000 years ago, four ice advancements brought a one-mile-high wall of ice into northern and northwestern Pennsylvania. Meltwater from each advancement found its way down the Susquehanna River, adding to its erosional rate.



diagram: This geological graph shows the slope of the Susquehanna River through much of Pennsylvania.


© Submitted
This geological graph shows the slope of the Susquehanna River through much of Pennsylvania.

Particularly at the end of the Ice Age, the additional meltwater from the glaciers created severe downcutting of the Susquehanna River, forming large potholes in the bedrock. It can be shown where the river once flowed about 200 feet higher than its present-day elevation. 

Eventually, around 10,000 to 8,000 years ago, the Susquehanna River had formed a 400-foot deep canyon where it flowed into the Chesapeake Bay. Today, sedimentation has filled in the canyon and helped create what we know of today as the Atlantic Coastal Plain.

Jeri Jones is geologist who lives in York County, Pennsylvania.

  • Intro: Killing the Chesapeake
  •    

  • The Winands: A family’s life from Susquehanna headwaters to the bay
  •  

  • Pennsylvania is failing the Chesapeake Bay – and how that affects you
  •  

  • Susquehanna River water goes south from Otsego Lake — figuratively and literally
  •  

  • Mountains & meteorites: How the Susquehanna River and the Chesapeake Bay were formed
  •   

  • How Amish farming practices and old mill dams harm the river & bay — and how to fix it 
  •    

  • Dammed if you dredge, dammed if you don’t: Conowingo’s toxic muck a vexing problem for bay
  •  

  • Raw sewage in the Susquehanna: Pa. ‘state government is basically defecating in the river
  •   

  • Dammed, drugged & poisoned: 3 iconic Susquehanna species struggle to survive
  •  

  • Hell-bent for Hellbenders: ‘The canary in the coal mine’ of the Susquehanna watershed
  •  

  • The ‘Dead Creek’: It literally runs red with acid mine discharge, poisoning the Susquehanna
  •   

  • The 444 Club: Boating the entire Susquehanna propels paddlers into another world
  •   

  • Fishing for monsters ‘out of the abyss’: Flathead catfish in the Susquehanna River
  •    

  • He got a brain-eating amoeba jet skiing on the Susquehanna – and beat the 97% fatality rate
  •   

  • He’s pulled 10,000 pieces of plastic from the Susquehanna – and he’s just getting started
  •     

  • Worst-case scenario for river & bay: climate change, flooding, dead zones, crab depletion
  •  

Continue Reading

About Antoinette G. Tucker

Check Also

Tremendous Bowl 2021 commercials: All the very best and worst ads, from Uber Eats and Jeep, to Geico and Cheetos

For numerous persons, Super Bowl Sunday is all about the large game. For other individuals, it is an excuse to indulge in delicious treats, even though all those ambitions are scaled way again this 12 months. And the sport always gives the spectacle of the halftime display. A huge element of the Super Bowl practical …