Big Rock and other glacial erratics

Up in the small patch of woods in back of my house is a large granite boulder that has been there for as long as I can recall.
It’s roughly a little under five feet tall by five to seven feet in width depending on where you measure it. As children, my siblings and I dubbed it ‘Big Rock’ and needless to say it was quite the kid magnet. We routinely played around and on top of it without anybody scolding us about how ‘dangerous’ it was. I don’t recall that any of us or the neighborhood kids who joined in, ever suffered any serious injury, unless you count the occasional skinned knee.

Noting other smaller rocks in the vicinity, we proceeded to name them Little Rock, Baby Rock, etc, but none of them had the charisma of Big Rock itself. Unfortunately I never asked my parents who built their house on the property if Big Rock was there to begin with or if it was dug up during construction. Given its size, resembling a beached whale, I suspect it was there all along while the forest grew up around it.

New England is filled with an abundance of rocks, stones and boulders of varying size and heft, causing annoyance to any one attempting to clear the land, creating challenges for hikers and food for thought to geologists. Large boulders like Big Rock are often referred to as glacial erratics , stones moved from their point of origin by glaciers. Depending on how the ice flowed, they may have traveled a great distance or only a short jaunt from the ledge they were torn off. Madison Boulder, one of the largest erratics located here in New Hampshire, is thought to have originated from the Whitten or White ledges located 12 and 4 miles respectively to the northwest. At 83 by 23 feet in size, it is thought to weigh in at 5000 tons so it gives an idea of the power of the ice sheets that came grinding down across our state during the Laurentide.

Countless other erratics can be found throughout the state, some with odd ball histories such as Boise Rock. This large boulder earned its name during the 1800’s after Thomas Boise, a teamster, was trying to make his way through Franconia Notch when he was caught in a fierce blizzard. According to local folklore, in order to avoid freezing to death he unsentimentally killed and skinned the horse he had been riding and used its hide to protect himself while hiding under the rock now bearing his name. His ploy paid off and searchers found him alive when hunting for him the next day.

Glaciers have left their mark everywhere here in New Hampshire. Crawford Notch shows the classic U-shape characteristic of valleys ground down by ice rather than eroded by a river. Glacial striations are visible in many places where ledge was exposed to the relentless scrapping of the Laurentide Ice sheet.

Other features such as moraines, kettles, potholes and cirques can be found scattered throughout the White Mountains. A good example of a natural pothole is the Basin, located in Franconia Notch. Rushing mountains waters that originate from Profile Lake and form the beginnings of the Pemigewasset River, wash out pebbles and sand which over the millennia have scoured an area of the local granite forming a beautiful natural basin 30 feet in diameter and 15 feet deep. Its polished appearance looks like the product of some sculptor but in reality it is Mother Nature’s work. Mount Washington’s Tuckerman Ravine, a popular magnet for adventurous skiers is a classic example of an old glacier cirque. Its classic bowl shape is the result of a local alpine glacier which formed during The Pleistocene age.

But above all else it is the glacial erratics strewn everywhere that are the main characteristic of New Hampshire and other New England states, adding expense to construction projects when they have to be moved, or aggravating farmers trying to plow their fields. But while we may curse their ubiquity, that hasn’t stopped us from making use of them, either as objects of interest for tourists or just as building materials to make a familiar sight in our state.