What are surface lakes glaciers?

Glacial Lakes: More Than Just Pretty Pools on Ice

Glaciers and ice sheets – those immense, slow-motion rivers of ice – are anything but static. They’re dynamic landscapes, constantly changing. And one of the most fascinating, and frankly, increasingly worrying, features of these icy realms are glacial lakes. These meltwater-fed lakes come in all shapes and sizes, each with its own quirks and profound effects on the glacier’s behavior and the surrounding world. Let’s dive into two key types: supraglacial lakes, those shimmering pools you see on the ice, and subglacial lakes, the hidden reservoirs lurking beneath.

Supraglacial Lakes: Puddles with a Purpose (and a Problem)

Imagine a bright summer day, and instead of a snow-covered expanse, you see brilliant blue lakes dotting the surface of a glacier. That’s a supraglacial lake. They’re basically any body of liquid water chilling out on top of a glacier. Now, these aren’t your typical permanent lakes; they’re often ephemeral, meaning they come and go. Some might stick around for months, even years, growing to be surprisingly large – we’re talking kilometers across and several meters deep! But get this: some can drain away in just a matter of hours. It’s like watching a giant bathtub empty in real-time.

How Do They Form? Think of it this way: the sun’s out, the ice is melting, and that meltwater needs somewhere to go. It collects in dips and hollows on the ice surface, forming these lakes. Simple, right? Most of this melting happens during the summer, or even from a good rain shower. Down in Antarctica, the party really gets started between November and February, when the sun is high in the sky.

Where Can You Find Them? Pretty much anywhere there’s a glacier. But they’re everywhere on the Greenland Ice Sheet, especially at lower elevations early in the melt season. As things warm up, they creep further inland. And in Antarctica? You’ll mostly find them on ice shelves, where the flat terrain makes for perfect meltwater pooling. Fun fact: in coastal East Antarctica, these lakes tend to cluster near where the ice shelf touches land.

Why Should We Care? Here’s where it gets serious. These lakes, as beautiful as they are, can seriously mess with the ice.

• Albedo Effect: The Dark Side of Blue: Water is darker than ice, right? That means it absorbs more sunlight. So, these lakes soak up the sun’s energy, leading to even more melting. It’s a vicious cycle.
• Speed Demons: Ever heard of a glacier suddenly speeding up? Supraglacial lakes can be the culprit. When they drain, the water can reach the base of the ice sheet, lubricating it and making it slide faster. We’re talking about drainage rates comparable to Niagara Falls!
• Ice Shelf Trouble: These lakes can be a warning sign. A bunch of them popping up can indicate that an ice shelf is unstable, and they’ve even been linked to collapses. Remember the Larsen B ice shelf in Antarctica? It basically disintegrated in 2002, and a proliferation of these lakes was a major red flag.
• Crevasse Creators: Imagine a lake big enough to crack the ice beneath it. Lakes over ~300m across can actually force water down into the glacier, creating a direct path to the bedrock. These “moulins” act like plumbing for the ice sheet.

The Climate Change Connection: Here’s the kicker. Since the 1970s, we’ve seen these lakes popping up at higher and higher elevations. Why? Because warmer air is causing melting further up the ice sheets. And because there’s more meltwater around, these lakes are expanding inland, a trend that’s only expected to continue.

Subglacial Lakes: The Hidden World Beneath

Now, let’s head beneath the ice. Subglacial lakes are bodies of water hidden under a glacier, typically under an ice cap or sheet. They form at the boundary between the ice and the bedrock below.

How Do They Form? Imagine immense pressure from miles of ice above. That pressure lowers the melting point of water, allowing it to exist as a liquid even in freezing temperatures. Over time, the ice melts, and that meltwater flows and pools, creating these hidden lakes. Some of these lakes have been isolated for millions of years! And get this: they’re probably refilled by water draining from those supraglacial lakes above, not just from the ice melting at the bottom.

Where Are They? Most of the subglacial lakes in Antarctica are found near ice divides, where huge drainage basins lie under the ice sheets. But we’re also finding more and more near ice streams.

What Are They Like? The water stays liquid because geothermal heat from the Earth balances the heat loss at the surface. And remember that pressure? It keeps the melting point low. Some lakes are also super salty, which helps keep them liquid.

Why Are They Important? These hidden lakes can affect how the ice flows by reducing friction at the base. They also create unique environments for microbes to thrive. Who knows what secrets they hold?

Glacial Lakes and Climate Change: A Two-Way Street

Glacial lakes, both on top and underneath, are deeply connected to climate change. As the planet warms, glaciers shrink, dumping more freshwater into these lakes. The increase in supraglacial lakes speeds up melting and ice flow, adding to sea-level rise.

And while these lakes can provide freshwater, that supply might not last as the melt becomes too much. Plus, glacial lake outburst floods (GLOFs), caused by dams failing, are becoming a bigger threat to communities downstream.

Final Thoughts

Glacial lakes are a vital part of glacial systems, influencing how ice moves, how much ice there is, and how much the sea level rises. Understanding these lakes is key to predicting the future of glaciers in a warming world. As climate change keeps changing our planet, studying these lakes will become even more important for managing the risks that come with these dynamic environments. They’re more than just pretty pools; they’re a window into the future.