Decorah impact crater

a unique window into the history of life on earth


Buried one hundred feet under the city of Decorah, there is an ancient impact crater, formed approximately 465 million years ago when a football-stadium-sized meteor collided with the Earth’s surface in central Winneshiek County. The Decorah Impact Crater is one of fewer than 200 recognized impact structures on the entire planet. In 2010 the fossilized remains of a nearly 6-foot sea scorpion, Pentecopterus decorahensis, were discovered within the now-buried crater basin.

Scientific discovery, 465 million years in the making


The #Decorahimpactcrater is History beneath our feet

What's New?

See Decorah’s Oldest Resident!

@ Luther College – Valders Hall of Science

700 College Drive Decorah

Decorah’s giant sea scorpion, the Pentecopterus decorahensis, is officially home! Join in exploring and celebrating the life-sized model of Decorah’s most famous fossil discovery, now in its long-term home in Valders Hall of Science at Luther College. Learn more about the discovery and how this creature may have lived 465 million years ago.

  • Go to Luther College’s main entrance / 700 College Drive
  • Stay left for Upper Campus.
  • Park in a visitor spot near the first building on the left, Sampson Hoffland Laboratories. Enter SHL.
  • In the lobby of SHL, stay right to enter Valders Hall of Science.
  • See Pentecopterus decorahensis in its display in the hallway!

The Decorah Impact Crater

Approximately 465 million years ago during the Ordovician Period, an impact event occurred in what is now Decorah, Iowa. The result was a crater with a diameter of 3.5 miles (5.6 km). 

Soon after the crater was created through the impact of the meteor, it filled with ancient sediment and then was buried under even more sediment. Millions of years later, the Upper Iowa River eroded some of that sediment away and created the bluffs and hillsides that now surround Decorah.

The Decorah Impact Crater discovery provides scientists with a new opportunity to learn more about impact events and crater processes. The crater basin also created a unique environment in which an exceptional fossil record was preserved, offering insights into life on Earth during a critical period in the evolution of complex life.

The Decorah Crater might still be undiscovered if not for the curiosity and persistence of local resident Jean Young and her work for the Iowa Geological Survey. Learn more about Jean by clicking on “Crater Discovery” below.

Frequently Asked Questions

Crater Discovery

Fossil Discoveries

Crater Impact Studies

Listen to the Story

The Ancient Sea Scorpion

The most famous fossil discovery from the Decorah Crater made so far is Pentecopterus decorahensis, a giant sea scorpion. The term ‘sea scorpion’ is an informal name for a type of arthropod called a eurypterid (yew-RIP-ter-id). Like other arthropods (insects, shrimp, lobsters, etc.), eurypterids had a segmented body and jointed limbs with a flexible organic exoskeleton. While It looked like a scorpion, it lived in water and used its tail for navigating rather than stinging. It also had paddle-like rear legs adapted for swimming.

Pentecopterus decorahensis was a large apex predator during the Ordovician period, approximately 465 million years ago. Adult and juvenile fossil species were discovered in a fossil bed under the Upper Iowa River near Decorah. The fossils were preserved in sediment layers formed where the shallow sea covering Iowa at the time flooded the Decorah Crater.

Learn more by clicking on the “Fossil Discoveries” icon above!

Listen to the Story

In this episode of “Rhymes with Decorah,” host Benji Nichols of Inspire(d) Media tells the incredible story of geologist Jean Young and the discovery of the Decorah Impact Crater. Long-time educator and NE Iowa resident Birgitta Meade joins to tell the story of Jean, who she also called a friend, right up to her passing in 2007. This episode is dedicated to all those who are willing to follow a hunch in life, and take action in their beliefs, no matter what others may say. 

Shop at the Decorah Visitor Center

Grab a piece of history for the whole family! Celebrate our local fossil celebrity, the giant sea scorpion Pentecopterus decorahensis.  

Stop by the Decorah Visitor Center, at 507 W Water Street, to purchase sea scorpion shirts and postcards designed by local Decorah Artist Mark Whelan. Shirts are available in adult and kid sizes. When you stop by we will talk about who would win in an underwater battle — you or the Pentecopterus decorahensis?! 

Decorah Crater Project Support

Understanding and celebrating the Decorah Crater is an important and growing feature of community pride and self-identification in Decorah and Winneshiek County. Join community members and organizations in supporting public outreach, school-based education, and tourism-promotion efforts based around the Decorah Crater, the unusual life that inhabited it, and the unique regional geologic history of the Decorah area. 

Donations of all sizes are appreciated to help this project grow! Donations are received and held by Northeast Iowa RC&D, a 501(c)3 organization and one of the partnering organizations working on telling the story of the Decorah Crater. 

Project partners are currently focused on two initiatives.

Pentecopterus decorahensis Model
  • Project partners have “brought home” a life-size model of Pentecopterus decorahensis that had been housed at the University of Iowa. The colorful model is on long-term loan to Luther College, where it will be placed on display for public viewing. In late Fall / early Winter 2022-2023, the model will be temporarily displayed at Impact Coffee in downtown Decorah.
Around the Crater Tour
  • Because the Crater is buried deep underground, there are no physical places to visit or easy-to-see evidence. This makes it challenging to understand the story of the Crater and also makes it difficult for the local community to promote the Crater as a reason to come visit Decorah. An “Around the Crater” Tour with markers placed at points in and around the Crater, a brochure/map, and a website will help overcome both of these challenges by providing interpretive and educational information about the Crater and offering numerous opportunities to cross-promote natural resources, outdoor recreation, Luther College, and Decorah’s numerous crater-inspired local businesses.

Laura Peterson, Professor of Environmental Studies, Luther College

Birgitta Meade, Decorah Educator

Tom St. Clair, Decorah Resident

Steve St. Clair, Decorah Resident 

Lilly Jensen, Northeast Iowa RC&D

Stephanie Fromm, Winneshiek County Development

Alyssa Ritter, Visit Decorah

Jessica Rilling, Decorah Area Chamber of Commerce

Hanna Schmitt, Winneshiek County Conservation


If you would prefer to donate via check, please send a check with “Crater Projects” in the memo line to the address below. 

Northeast Iowa RC&D
PO Box 916
Postville, Iowa 52162


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