thumb|300px|An ice volcano over [[Lake Michigan]]
thumb|300px|Ice volcanoes in [[Ystad, Sweden, 2018]]
An ice volcano is a conical mound of ice formed over a terrestrial lake via the eruption of water and slush through an ice shelf. The process is wave-driven, with wind providing the energy for the waves to cut through the ice and create formations that loosely mimic the shape and activity of volcanoes. After being ejected into the atmosphere, the liquid water and slush freeze and fall back to the surface, growing the formation. Ice may also be erupted. The phenomenon is most often observed along the southern coast of Lake Erie and Lake Ontario, when the temperature is below freezing and the wind blows onshore with a velocity of at least . They are known to reduce coastal erosion there. The formations are temporary: they are frequently destroyed by storms and warm weather, and once the lake wholly freezes over, eruptions are no longer possible.
There is no consensus name for this phenomenon. Due to its visual similarity to volcanism and particularly cryovolcanism, the term "ice volcano" is frequently used, but it remains controversial.
Formation
These features are distinct from pressure ridges, which are uplifts formed by the compression of ice against a shoreline or another floe. Instead, ice volcanoes are created by waves colliding with irregularities at the edge of an ice sheet. The abnormalities concentrate the wave energy in a small area, where the ice is eroded to form a V-shaped channel. Spray, ice, and slush splashing out of the feature create a volcanic cone at the channel's shoreward end. This process takes only a few hours. Formation is more thoroughly suppressed by powerful storms, which erode the ice too fast for mound creation.