October 22, 2012
WHERE’D ALL THE SAND COME FROM?
EAST MONTPELIER, VT – Driving south on Vermont Route 14 from Woodbury to East Montpelier, you can’t help but be struck (if you’re paying attention at all) by the high banks of fine sand on the far side of the tiny Kingsbury Branch of the Winooski River. The stream is far too small and far down in the valley to have deposited that sand so far above it; and the valley is too big to have been carved by so little water just since the last Ice Age. So what happened?
Heading south on Interstate 89 and approaching Sharon, you look across the White River valley, and there they are again: great high banks of sand and gravel far above the river, obviously created by a stream or a lake, or a combination of both. They’re a town road agent’s dream: enough material for a lifetime of sanding and repair work. But how’d it get there?
My career in geology started off with a show of early foot in 1953. Our Physical Geology 101 class had been studying land forms – mountains, volcanoes, beaches, swamps – and their origins, and we had just the day before been introduced to solifluction, the flowing downhill of saturated soil in muddy little waves. Now, on our first field trip, Professor Moke stood with us in the valley of Killbuck Creek and pointed out a series of little terraces running horizontally across the grassy hillside above us. “What do you suppose caused those?” he asked.
Solifluction was the universal learned consensus. Some freshman Presbyterians were even writing it in their notebooks. But I didn’t go to school in New England for nothing; I could smell a trick. “Looks to me,” I said, “like cow paths.” Which indeed they were. Imagine my amazement that my smart-ass answer had not made me popular with my new classmates.
In subsequent semesters, as I further pursued a major in what’s now called Earth Science, I foundered on the reefs of classes more esoteric than geomorphology, and retreated into the humanities, where I belonged. But that early interest in land forms, and how they got that way, has persisted. How is it that the water of Lonesome Lake above Franconia Notch is alkaline and supports a healthy brook trout population, even though it’s cradled in a basin of acidic bedrock? If Mount Ascutney is indeed the ancient granite plug of a volcano, why is there no evidence of eruptions around it? The sloping sides of West Wheelock Street in Hanover are, beneath their ground cover, pure, fine-grained sand What’s with that?
Paddling down the Tree River in Arctic Canada toward Coronation Gulf during the brief summer of 1991, my friends and I were intrigued, as we crossed the 700-foot contour, to find the river water changing from crystalline to silty, and the banks from rock to gray mud pocked with ground squirrel holes and littered with unfossilized clam shells. It was clearly the bottom of a fairly recent, but extinct ocean. What had happened? We puzzled about it for a while, and finally figured it out.. The glacier had retreated there only about 8000 years earlier, and since then the land, relieved of the massive weight of the ice, had been rising; we knew that from the number of canyons and abandoned channels we’d encountered. But 700 feet in 8000 years? That’s about an inch a year, which seems unlikely. But once we got to salt water, we found ancient Thule stone houses that had once been on the seashore – as evidenced by middens of shells – hundreds of feet higher.
I was glad we didn’t have a scholarly text or person with us, because the mystery of the silent, rising land and the roar of the infant canyons were far preferable to a monograph.
Our local geological mysteries have been pretty well teased out by generations of graduate students and their distinguished professors. Probably the most spectacular is the formation and disappearance of Glacial Lake Hitchcock. It once stretched all the way from Middletown, Connecticut, where it was impounded by a dam of glacial till and boulders, to near present-day St. Johnsbury, Vermont. Paddling down the Connecticut River between, for example, Newbury and Lyme, you can see here and there in its banks layers of sand and silt, (“varves”) thick and thin, deposited by annual fluctuations in the river’s flow – thick in the summer, when the ice sheet to the north melted more rapidly, and thin in the winter, when the flow slowed to a trickle. The top of the banks more or less mark the floor of the lake.
Leaving Hanover and driving eastward up Greensboro Road, you’ll see no stone walls anywhere on the floor of the valley. But at the foot of Etna, Mink Brook starts to rise, and within a few hundred yards you encounter a homestead named “Mending Wall,” and just above it, another stone wall-enclosed yard. Glacial Lake Hitchcock penetrated up the Mink Brook valley to what’s now the foot of Etna and buried it in sand. The best way to experience it is in a kayak or canoe during spring spate: Suddenly the bottom changes from boulders to silty mud.
The road agent’s treasure high up in Sharon? Lake Hitchcock made the White River valley a lake for centuries. The huge gravel banks south of US Route 302 in East Barre, where now the Rail Branch flows toward downtown Barre, were deposited in Glacial Lake Winooski, formed when ice dammed the river’s normal westward flow and diverted it south toward the White River.
It’s nice to know all this stuff, though, like cow trails, it doesn’t win you any friends. But it’s really exciting to consider what these places looked and felt like as the ice retreated northward: woolly mammoths, caribou, muskoxen, elk, migrating waterfowl by the millions, and early human hunters tentatively following the herds northward onto the newly fertile tundra.