What They Are: Pressure ridges are places in frozen bodies of water where the ice has cracked and been forced upward.
How They Form: The ridges are formed by expanding and contracting ice. When the temperature drops, the ice contracts and cracks form. These cracks fill with water and refreeze. When it warms up the ice expands and it is forced upward along the cracks. The motion that forms the ridges is similar to how tectonic plates create mountain ranges.
How To Spot Them: You can usually see the ridges from miles away. They are long serpentine-like strings of ice sticking up vertically from a frozen lake or ocean, often 15 to 20 feet high in places.
Why They’re Dangerous: With the power of millions of pounds of ice cracking and being forced upward, water often leaks to the surface creating large slushy areas that can weaken the ice. Avoid the slushy areas or you could get your machine stuck and soak your boots. Often, in areas where the ice has separated by more 2 two feet, only an unassuming, thin layer of snow covers them. If you’re not careful, you can go through the ice. In some areas along a pressure ridge, ice has been forced down and water has seeped up from the lake covering it over. In areas like this you will get two layers of ice. If the crack happened recently, the top layer of ice may only be an inch or two thick and the bottom layer could be eight feet below it. It’s best to stay a safe distance away from them while following their route.
Why They Suck: Pressure ridges look pretty cool, but they stop looking that way quickly when there is one blocking your way. It can take hours to find a place to cross and you sometimes have to follow them for miles until you find one. In other words, they’re a navigation nightmare.
How To Cross Them: Stay tuned for Friday’s video post…