- People & Economy
- Nature & Environment
- Heritage & Recreation
- Issues in the Basin
The Basin’s last significant geologic event occurred relatively recently in geologic time with the beginning of the Ice Age approximately 3 million years ago. During this time, glaciers advanced and retreated across North America. During the last glacial advance, the Champlain Valley and most of the surrounding mountains were covered with a sheet of ice over a mile thick!
The movement of the ice caused intense erosion and weathering of the mountains, which is shown by their rounded shape today. Evidence of glaciation can be seen throughout the Lake Champlain Basin, from rounded glacial valleys to eskers (rocky ridges resulting from stream deposits).
When the earth began to warm some 15,000 years ago, the ice retreated and acted as a dam in the north end of the Champlain Valley, forming Lake Vermont from melted glacial waters. During this time period, both present day Plattsburgh, NY and Burlington, VT were underwater and Mount Philo was an island. Today we can identify layers of clays in the lake bottom that are further evidence of Lake Vermont.
Approximately 13,000 years ago, further retreat of the glacier and depression of the earth’s surface from the weight of the ice allowed marine waters from the St. Lawrence estuary to flood the Basin. The Champlain Sea, an arm of the Atlantic Ocean, formed. Many marine animals, including beluga whales, Atlantic cod, seals, and blue mussels lived in the Champlain Sea. In 1849, railroad workers found a beluga whale skeleton in Charlotte, VT, which is now on display at the University of Vermont. Many other fossils of the Champlain Sea time period have been found in Canada and in sediment beneath today’s Lake.
With the weight of the ice removed, the earth’s surface slowly rebounded, cutting off the supply of salt water from the St. Lawrence River around 10,000 years ago. Rainfall and runoff turned the saltwater of the Champlain Sea back to freshwater, creating present day Lake Champlain.