The day was drawing to a close. All of us were tired, and some of us were getting decidedly cranky. We’d been paddling for hours along a narrow river, through country that had the character of a waterlogged sponge. In fact, that’s really what it was—a well-watered lowland forest, rich in black spruce, shrubby leatherleaf, and bog flowers. A great place for turtles, herons, ducks, muskrats and beaver. Not so great a place for camping, however. Still, we knew that a good campsite wasn’t far away. We were looking for an esker.

The sky darkened. Our shadows lengthened and then disappeared altogether. The sun sank below the horizon. Finally, just as the last of the light was going, we rounded a bend and saw a long, low ridge rising up alongside the river. We’d found our home away from home. We weren’t the first folks to do so. The scattered remnants of a fish-drying rack could be seen on the river bank, lying where some earlier gale had brought a wet-footed gray birch crashing down upon it.

We dragged ourselves and our gear up a short, steep trail to the summit of the ridge. The narrow crest was level and dry—scarce amenities in the watery lowlands of central Ontario. Birch and aspen leaves trembled in a gentle breeze that helped keep the evening mosquitoes at bay. Chickadees wished us good night. Then they were silent. The first notes of the frog chorus began. Somewhere, not too far off, a loon called. In no time at all we’d pitched our tents on the stoney, sandy soil and were busy making a late supper. It wasn’t the first time I’d camped on an esker, of course—eskers are common throughout the once-glaciated regions of the northeastern United States, eastern and arctic Canada, and Scandinavia—but it was the first time I’d actually gone looking for one.

Often known locally as “hogbacks” or “horsebacks,” eskers aren’t among the most spectacular landscape features. From the seat of a canoe or kayak, an esker looks like nothing so much as a long, low, undulating ridge. Seen from near its base, however, an esker rises steeply. If there isn’t a landing carved into the flank or a small beach at its foot, you’ll have a hard time scrambling out of your boat and up the slope. As you climb, you’ll notice that the esker is formed from gravel, cobbles and sand. Look closely at the stones at your feet, and you’ll see that they have very few sharp edges. Each stone looks as if it’s been tumbled about for a long time, like a rough-polished gem. And so it has. The gravels and cobbles of eskers have been polished by moving water, just like the stones in a riverbed. And, indeed, eskers mark the paths of long-vanished rivers.

Here are a few photos of an esker snaking along the forested flank of a mountain in the northern Adirondacks, beginning with a portion which is bifurcated, or split:

Note the steep sides. And here’s a view from further along, showing where a stream has carved down through the esker, allowing a pair of mountain tarns to drain off the slope and empty into a lake several hundred feet below:

And another view down the long axis of the esker:

So how, then, did eskers form? They’re a relic of the most recent Ice Age, and the mark the paths of ancient rivers. … Read more…

 
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