Walking on Clear Ice
Most of the time when we see a frozen body of water, like a lake or a pond, the ice is cloudy or white. You typically cannot see to the bottom, or anywhere below the ice’s surface. However, Youtuber Thomas N and a friend were hiking in the High Tatras Mountains in Slovakia when they happened upon this perfectly clear lake. The ice is so clear beneath his feet that it looks like he is floating above the pebbles at the bottom of the lake.
So what is it that makes the ice so clear here? Is the water different? The temperature? The key is to figuring out what makes the ice crystal clear, is actually to think the opposite way. Think about magma as it flows from a volcano. When it cools it forms in a few different ways. When it cools quickly, you get lava rock. Rough rock with many holes that formed as air escaped when the magma rapidly cooled. When the magma cools slowly, you get Obsidian, or volcanic glass. Obsidian is smooth, shiny, black, and sharp.
Now, think about ice. When ice cools quickly it gets that cloudy effect. Air bubbles, oxygen, and water impurities get trapped inside the ice. It freezes too quickly to let those all escape. With the lake in the video, it is likely that the water is more pure than water you may see regularly in ponds, lakes, or even ice cubes. It may have run down from a melting glacier and then proceeded to freeze slowly, perhaps in layers, allowing all the air and impurities to escape.
It probably helps that it appears the hikers are walking on a shallow portion of the lake. This allows for less light to refract and for the ice to appear more crystal clear. Either way, the video is absolutely amazing!