For most of us, our first exposure to geology in school was the study of the Grand Canyon. Awed by its immense size and varying nature, it seemed improbable that a mere river could cut such a wide, and deep swath through the earth, even with millions of years to get the task completed. At close to 300 miles long, up to 18 miles across, and a mile deep, the Grand Canyon inspires awe, with about 5 million visitors going to see this wonder each year. Even though new evidence suggests part of the canyon formed millions of years before the Colorado River existed, the power of water, and erosion are on display at this American landmark.
For those who grew up in the Upper Valley (of which I am not one), I’ll bet that alongside the study of the Grand Canyon was the study of the Quechee Gorge. Dubbed ‘Vermont’s Little Grand Canyon,’ the gorge runs a mile long, and 165 feet deep. Miniscule by comparison with the behemoth Grand Canyon – yet the largest such feature in Vermont – thousands each year visit the Quechee Gorge. Many observe it from the Route 4 bridge (which has a fascinating history itself), while others make the trek to the bottom of the gorge by accessing the trails in the Quechee Gorge State Park.
Unlike the new evidence showing the Colorado River might not be the sole contributor to creating the Grand Canyon, water – and the Ottauquechee River in particular – are responsible for the creation of the Quechee Gorge. The Quechee Gorge is a new phenomenon by comparison to many of the world’s gorges, dating back thousands of years, but not millions. Still, how the gorge happened to be is an interesting story, and one regional geologists and geology students have studied for some time.
As we all learned in school, thick glacial ice covered much of North America during the last ice age. Almost 20,000 years ago, as temperatures warmed, that glacial ice retreated northward. Ice turned to water, forming rivers and lakes. In New England some 14,000 years ago, what is now the Connecticut River Valley, was once a glacial lake named Lake Hitchcock.
The lake formed because of a glacial moraine (or rock and earthen dam) that formed in the area of present-day Rock Hill, Connecticut. Lake Hitchcock – named after 19th-century American geologist Edward Hitchcock – stretched for about 200 miles south to north, and up to 20 miles across, at its peak about 14,000 years ago. Arms of this massive lake extended into the river valleys that feed into the present Connecticut River. The Ottauquechee River was one such river that fed into the lake.
Lake Hitchcock existed for about four thousand years. Around 13,000 years ago, the land in present-day Connecticut holding back the voluminous waters of this glacial lake broke down, causing the lake to drain, and form the Connecticut River basin.
Forming the gorge
The draining of Lake Hitchcock resulted in the forming of the Quechee Gorge. Soft, loose, sandy soil covering the area of the gorge was one reason. Ed Meyer, research scientist and senior lecturer at Dartmouth College, says a contributing factor to the gorge creation was the fact the Ottauquechee formed a delta where it flowed into ancient Lake Hitchcock. That delta left sand and soil that quickly washed away as the lake drained. In fact, the ancient Ottauquechee took a different course before the lake drained, says Meyer. The river’s current course was established with the draining of the lake, and the creation of the gorge.
According to David West, professor of geology at Middlebury College, there were factors other than the soft delta soil that contributed to forming the gorge. “It was a combination of things that resulted in the formation of such a deep gorge in this location,” says West. “First, there were likely some zones of weakness in the bedrock prior to the formation of the gorge,” he says. “The catastrophic draining of post-glacial Lake Hitchcock... likely resulted in the channelization of tremendous amounts of water which scoured out the gorge to essentially its present configuration.”
Meyer adds that the draining of the lake was not a single event, but likely happened in stages over time. According to research scientist Matt Bigl, the actual draining of Lake Hitchcock began 13,300 years ago, with the lake lowered to near the level of the Connecticut River about 12,300 years ago; meaning a 1,000-year draining event. The forming of the gorge, from the beginning with the draining of Lake Hitchcock, to what we see today, is a very short time for the formation of such a natural occurring edifice, Meyer says.
Though the forming of the gorge happened relatively quickly with the draining of Lake Hitchcock, we all surmise that erosion continues in the present day, though at a much slower pace than we might expect. “I can’t give you an exact number on that rate; probably less than a millimeter a year,” says West. “Of course there are higher erosion rates during times of flooding, but normally erosion is occurring very slowly.”
A recent weather event that altered the gorge was Tropical Storm Irene in 2011. Meyer says there were some “spectacular landslides,” in certain areas of the gorge, upriver from the bridge, as a result of Irene.
An area of study, work, and beauty
Having a deep cut into the earth such as the Quechee Gorge offers an excellent opportunity for geologists and students to study local geological conditions. “It offers good exposure to the local bedrock and schist,” says Meyer. His Dartmouth students make regular trips to the gorge in their geology studies, Meyer says. “It’s a great natural lab for students.”
Meyer notes that in most areas, the regional bedrock is covered with earth and vegetation; that’s not the case at the gorge. West concurs, saying, “Usually bedrock in a deeply eroded mountain belt like the Appalachians is mostly covered in sediment, and we only see glimpses of it at the surface, but here we have a very long and uninterrupted view of the upper part of the Earth’s crust, and that’s helpful.”
The creation of the Quechee Gorge resulted in many benefits beyond the ones enjoyed by those that study geological history. Recent history points to the establishment of mills and water powered energy sources founded along the churning waters of the Ottauquechee. Of course, it also contributes to the vital tourist industry of the area today.
Those interested in a close-up view of the rich geologic history of the gorge can explore this unique and interesting part of Vermont's geography by taking the hiking trails to the river below.
As one descends down the hiking trails into the gorge, it is not difficult to imagine torrents of rushing water from the ancient lake spilling over the bedrock found in the gorge. The power of water, carving out a deep crevice in the land, is apparent even today. What remains from the events of the past 12,000 or so years is truly a wonder of the region.