The beginning of winter is a time of transformation. Ice coats the rocks and grasses of Lake Champlain’s shoreline, and begins to creep out over the freezing shallow water. Snow falls and melts away again. A cold night draws thick layers of fog over the lake’s surface, like a soft wool blanket, as the water gives up its summer heat to the air.
In the midst of these changes there is a lake phenomenon that seems more at home in the extreme cold of the arctic than familiar Lake Champlain. Commonly called ice volcanoes, this phenomenon is unique to large northern lakes and oceans, where powerful waves send “eruptions” of water through the ice. (See LCC’s video above of ice volcanoes forming along the North Hero shoreline.)
As the name suggests, ice volcanoes form in a similar way to geologic volcanoes. As erupted water falls back to the ice it freezes in layers, building up around the “vent” to form a cone. True volcanoes build up in the same way, only with layers of molten rock instead of ice. However, unlike their namesake, ice volcanoes are powered by wave action rather than heat.
When ice first begins to form along the shoreline it is fragile, and easily broken by waves. The waves then pile the pieces on top of each other, freezing and re-fragmenting them, until there is a thick ice shelf along the water’s edge. For ice volcanoes to form the temperature must drop below freezing, and the wind must be blowing at least 24 miles per hour. This strong wind drives powerful waves across the large water body, which are then forced under as they hit the ice shelf. With the ice shelf above and the rising ground below the waves’ power needs to go somewhere, and it finds an outlet in one of two ways.
Most commonly, the waves’ power is concentrated at irregularities in the ice shelf’s edge. The waves cut into these irregularities, and quickly erode a “V” into the ice. As the water hits the point of the V it sprays up, and the fallen spray freezes around the point in an arc. Over time the wide mouth of the V freezes over, and the layers of spray build up into a cone. Wave action from below continues to jet water out of the center, giving the ice mound the appearance of a volcano.
In other cases, the waves go deeper and don’t cut into the ice’s edge. Instead they roll under the ice shelf, where they seek out cracks and flaws to break through. There are often weak spots where the newly-formed ice broke and re-froze, and the waves are able to force these cracks open and vent water through the holes. The formation of this version of the ice volcano is then much the same – water falls and freezes in layers, while eruptions continue from the center.
Watch Lake Champlain continue to transform as winter sets in.