On a stormy winter day on the Great Lakes, a cone of ice on the shore suddenly blasts a plume of water and slush into the air. These “ice volcanoes” are built by waves, not magma, and they range from knee-high mounds to cones around 10 metres tall.
How ice volcanoes form
Ice volcanoes start at the edge of a shelf of ice that grows out from the shore. Researchers at Michigan Technological University, who documented the cones along Lake Superior, describe the sequence like this:
- Strong onshore winds drive waves towards the frozen shelf.
- The waves concentrate at irregularities in the ice edge and carve a V-shaped channel.
- Water and slush are forced up through the channel or through cracks, and the spray freezes and falls back around the opening.
- Layer by layer, the frozen spatter builds a cone. A single eruption can add several centimetres, and a cone can take shape in only a few hours.
Once the shelf extends further into the lake, waves keep running underneath it and push water up through existing cones, so even a cone surrounded by ice can still be active.
The weather they need
Three things have to come together. The air must be several degrees below freezing, so that spray freezes instead of melting the cone. The lake needs to be forming shore ice. And the waves must be big: roughly a metre high or more, which usually means storm-force onshore winds of at least 40 km/h (25 mph). That is why eruptions are most dramatic during snow squalls and winter storms.
Ice volcanoes are seen most often along the southern shores of Lake Erie and Lake Ontario and along Lake Superior, and a study published in 1973 described cones on Lake Erie near Dunkirk, New York.
Shapes, sizes and where cones line up
Cones range from under a metre to about 10 metres high, and eruptions taller than 10 metres have been observed. The biggest usually grow far from shore, where offshore sand bars and rock reefs make waves break hardest. The Michigan Tech team found that cones tend to form in evenly spaced arcs that follow the shoreline, a sand bar or a reef, and get larger towards the lake. Parallel bars can produce several arcs one behind another.
Borrowing terms from real volcanoes, the researchers sorted the cones into broad “shield” and steeper “stratovolcano” shapes. Cones at the very edge of the shelf are usually breached, open on the lake side, while those that form further back stay symmetrical. A rarer type, the “cold spot” cone, stands alone near shore and seems to form where water breaks through a weak point in the ice.
Watching ice volcanoes safely
Ice volcanoes draw winter visitors, but shore ice can hide open water and the cones themselves are often hollow. Watch from the beach or a lookout, keep off the shelf ice and never climb a cone for a photo.
For other Great Lakes ice spectacles, see Lake Superior Ice Stacking: Dawn LaPointe’s Duluth Shoreline Film and Lake Superior’s Mainland Ice Caves: Sandstone and Winter Formations.
Related reading
- Ten Volcanic Landscapes: Cones, Craters and Mountain Settings
- A Wingsuit Display Above Mount Bromo
- Kawah Ijen’s Blue Fire: Sulfur, Photography and the Crater Landscape
- Jamie Harkins and 3DSD: Anamorphic Beach Art in Full
- Tongariro National Park: Volcanoes, Māori Heritage and Changing Seasons
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