What is a stratified drift?

Stratified Drift: When Glaciers Sort of Clean Up After Themselves

Ever stumble upon a pile of rocks and sand that looks like it was meticulously layered? Chances are, you might be looking at stratified drift. This stuff tells a fascinating story about glaciers and the wild power of meltwater.

Now, “glacial drift” is a pretty old-school term, dating back to when folks thought giant icebergs were responsible for spreading all sorts of sediment around the globe. While the iceberg theory didn’t quite stick, the term “drift” did, and it basically refers to anything glaciers hauled and then dumped. But here’s where it gets interesting: not all glacial deposits are created equal.

Think of it this way: imagine a glacier as a messy roommate. It bulldozes everything in its path – rocks, dirt, the occasional unfortunate tree – and leaves it all in a jumbled heap. That’s glacial till: a chaotic mix of unsorted stuff. Stratified drift, on the other hand, is what happens when the glacier’s meltwater decides to tidy up a bit.

So, what exactly is stratified drift? Simply put, it’s glacial drift that’s been sorted and layered by meltwater. The meltwater acts like a natural sifter, separating sediments by size and weight. Heavier stuff, like gravel and sand, gets dropped first, while the lighter, finer particles of silt and clay travel further before settling down. This sorting action creates those distinct layers that give stratified drift its signature look. It’s like nature’s way of making a layered cake, only with rocks and dirt instead of frosting.

There are a couple of main types of stratified drift, depending on where they end up:

• Ice-contact stratified drift: This is the stuff deposited right next to the ice, or even underneath it. It’s a bit of a free-for-all, with sediments changing abruptly and sometimes getting all warped and bent as the ice melts. Kames (those steep-sided mounds) and eskers (long, winding ridges) fall into this category. Eskers are particularly cool – they’re basically the fossilized remains of ancient streams that flowed underneath the glacier. Imagine that!
• Proglacial drift: This type is carried further away from the glacier by meltwater. Think wide, open spaces like outwash plains and valley trains. Outwash plains are like giant, sandy aprons spread out in front of the glacier, formed by braided streams depositing sediment far and wide.

Why should you care about stratified drift? Well, for starters, it can be a hidden source of clean water. Those sandy and gravelly layers make excellent aquifers, storing and filtering groundwater. Plus, all that sand and gravel is super useful for building roads and bridges.

But maybe the coolest thing about stratified drift is what it tells us about the past. By studying these deposits, geologists can piece together the history of glaciers, figure out which way the meltwater flowed, and even estimate how big the ice sheets used to be. It’s like reading a history book written in stone (and sand, and gravel).

You’ll often find stratified drift in valleys and lowlands that were once covered by glaciers or their meltwater streams. These deposits can be incredibly thick, with layers upon layers of different sediments stacked on top of each other.

Think about places like the plains of the Midwest or the river valleys of New England – a lot of that landscape was shaped by the deposition of stratified drift. Next time you’re driving through one of these areas, take a look around. You might just be cruising over a piece of glacial history.

Oh, and one more thing: you might hear the word “stratified” used in statistics, like in “stratified random sampling.” It’s a totally different context, but the basic idea is similar: dividing things into layers or groups to get a better understanding of the whole picture. So, whether you’re talking about rocks or data, “stratified” is all about recognizing the importance of layers.

So, there you have it: stratified drift. It’s more than just a pile of rocks and sand – it’s a window into a world of glaciers, meltwater, and the ever-changing landscape. And who knows, maybe next time you’re out for a hike, you’ll stumble upon some stratified drift and impress your friends with your newfound geological knowledge!