What is basal ice?

Basal Ice: The Glacier’s Secret World Underneath

Glaciers: we often think of them as these massive, frozen rivers, right? But what’s really going on beneath all that ice? While we tend to focus on the fresh snowfall up top and the meltwater trickling down, there’s a whole other world hidden at the bottom – the realm of basal ice. And trust me, it’s way more interesting than you might think.

Basal ice is basically the foundation of a glacier, that layer right against the bedrock. But here’s the thing: it’s not just regular ice that froze from snow. It’s special. It’s formed and shaped by all sorts of crazy interactions with the ground below, and that gives it some seriously unique properties. Think of it as the glacier’s gritty underbelly, full of secrets about how it moves, erodes the landscape, and even what the environment was like thousands of years ago.

So, what makes basal ice so different? Well, for starters, it’s often packed with debris – rocks, sediment, you name it. The crystal structures can be pretty wild too, and in some glaciers, a lot of it is what we call “regelation ice.” But how does this stuff actually form?

There are a couple of main ways, and both are pretty fascinating. One is ice accretion. Imagine the glacier sliding over bumps and obstacles in the bedrock. The pressure on the upstream side causes the ice to melt a little. Then, that meltwater flows around to the downstream side and refreezes, adding a layer of ice to the bottom. It’s like the glacier is slowly building itself a new foundation, layer by layer.

The other way is through redistribution and incorporation. Basically, the glacier just bulldozes over whatever’s in its path – sediments, rocks, whatever – and mixes it all into the basal ice layer. It’s like a giant, icy blender.

All this gives basal ice some pretty distinctive characteristics. Like I said, it’s usually loaded with debris. I’m talking way more than you’d find in the ice higher up. Sometimes it’s just a little bit, but other times it can be up to 90% sediment! Can you imagine? That’s more rock than ice!

The crystal structure can be different too. Regelation ice, for example, often has a layered look. And all that squeezing and grinding near the bedrock can really mess with the crystal structure, making it even more unique.

The chemical makeup of basal ice is also a telltale sign. Depending on how it formed and what kind of rock it’s been in contact with, it might be rich in certain minerals. You can even find traces of gas that were trapped in the water when it froze. It’s like a chemical fingerprint that tells you about the glacier’s history.

And don’t forget temperature! If the base of the glacier is warm enough to melt, you might not find much basal ice at all. But in colder glaciers, you can get layers of basal ice that are several meters thick.

So, why should you care about all this? Because basal ice plays a huge role in how glaciers behave. For one thing, it helps them slide. That layer of water and sediment at the bottom acts like a lubricant, reducing friction and letting the glacier move faster. It also deforms more easily than regular ice, which helps the whole ice mass flow.

Plus, basal ice is a major player in erosion. As the glacier grinds along, the debris in the basal ice acts like sandpaper, scouring the bedrock and carving out valleys. All that sediment gets transported and deposited somewhere else, shaping the landscape in a big way.

But here’s the coolest part: basal ice can also be a treasure trove of information about the past. All that debris and organic matter trapped inside can tell us about what the climate was like thousands of years ago. We can find clues about past vegetation, temperatures, and even the composition of the atmosphere. It’s like a time capsule frozen in ice!

Scientists are constantly trying to learn more about basal ice. They drill ice cores, explore subglacial cavities, and study the ice that’s exposed at the edges of glaciers. They use all sorts of fancy techniques to date the ice and analyze the materials inside. For example, radiocarbon dating can tell us how old the organic material is, while cosmogenic nuclide dating can help us figure out how long rocks have been exposed to the elements.

Basal ice is a hidden world, but it’s a crucial part of the glacial system. It affects how glaciers move, erode, and transport sediment. And it holds valuable clues about the Earth’s past. So next time you see a glacier, remember that there’s a lot more going on beneath the surface than meets the eye.