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INTRODUCTION. Inland and distant from tectonic boundaries, Pennsylvania is not well known in the geological community for its volcanic activity. Despite this, “ice volcanoes” are a phenomenon well known to those who frequent the southern shore of Lake Erie during the winter. These volcanoes are not volcanoes in the traditional sense of molten rock and ash; they are cones of ice, sand, rock, and snow formed when wind and wave action sprays and freezes water into shapes that resemble volcanoes. Because these features have somewhat ambiguous shapes and there are not many firsthand observations of how they form, these terrestrial features have also been locally referred to as mounds, cones, and dunes. These terms do not convey the mechanisms of formation particularly well, so I follow the standard of referring to them as “volcanoes” as referred to by Fahnestock and others (1973) in their discussion of features found offshore of New York. As detailed in the 1973 article by Fahnestock and others, ice volcanoes form when the air temperature is below freezing but the water is still liquid, the wind direction is toward the shore at greater than 11 meters/second, and there is lake ice anchored to land (also known as “fast ice”) for waves to break against. Weather conditions in Presque Isle State Park in Erie, Pa., created chains of ice volcanoes that were observed on February 12 and 13, 2022. ICE VOLCANOES IN PENNSYLVANIA. The ice volcano shown in Figure 1 is roughly one meter tall from its base, approximately one meter wide at its “caldera” rim, and five meters from the shore. The slush, small ice blocks, and thin ice in the background all formed overnight. Ice volcanoes form when waves break against fast ice, gradually building up a large levee that is tallest near the water and slopes gradually away. The irregular scalloped shape of this ice levee causes waves to focus energy on the recessed surfaces of the levee that are more inland. Here, the water, slush, beach sand, and ice blocks crash against the funneled surface, resulting in some of this material being deposited on top of the ice levee and frozen into place, and the remainder draining through a lake-facing vent. Even one wave can add several centimeters of new material to a volcano. With enough time and sustained wind, a large ice volcano of up to 5–10 meters can form. Although shown as refrozen (Figure 2, right side), open water during a period of warm weather earlier in the week was able to Figure 1. A well-formed, representative ice volcano. reach the ice volcanoes. Wave action then caused some disintegration of the ice volcanoes into ice blocks. The glistening and polished surfaces of the foreground volcanoes indicate new accretion before the lake rapidly froze over the night before. Note the vents in the central throats that face the lake. If temperatures remained consistently cold after this photograph was taken, a new ice levee and set of ice volcanoes could form off to the right of the photograph. Page 20 Pennsylvania Geology Spring 2022 One of the extinct ice volcanoes is approximately 2.5 meters high from its base, 1.5 meters wide at its crater, and 10 meters from shore (Figures 3 and 4). This feature is included in the nearer of two parallel chains of ice volcanoes, and the blocky rubble shown at the base indicates a Figure 2. Older ice volcanoes reinvigorated by a recent thaw and refreezing. deposition of a “conglomerate” of lake water, slushy blocks, rounded ice cobbles, and a matrix of lake sand during the formation of a new ice levee behind the farther ice-volcano chain. Chains of ice volcanoes and ice levees can protect beaches at Presque Isle State Park from erosion during winter storms. CRYOVOLCANISM. Volcanism where nonsilicate volatiles are erupted into an environment below their freezing point is generally referred to as “cryovolcanism.” While technically applicable to circumstances at Lake Figure 3. Internal structure of an ice volcano. discovery of possible cryovolcanoes on Pluto, Titan, Ceres, Europa, Enceladus, Triton, Quaoar, and other icy bodies in the solar system. The image here (Figure 5) may resemble the surface of Jupiter’s moons Ganymede and Callisto; both are silicate Erie, this term may be more familiar to those following scientific developments in planetary science, such as the bodies with water-ice crusts and paradoxically Figure 4. The exterior of the ice volcano in Figure 3. The base of this volcano is approximately 8 meters wide. Page 21 Pennsylvania Geology Spring 2022 dark albedos. In the case of Jupiter’s moons, impacts from foreign bodies and/or clays from the silicate crust coat the surface and darken it. At Presque Isle State Park, wind and water help to cover sand over snow and ice. A FRIENDLY REMINDER. Winter signs in Presque Isle State Park warn visitors to avoid climbing on ice volcanoes; this is due to the inherent instability of these ice features. As the central conduit of an active ice volcano is liquid water, it is very possible to fall into Lake Erie. If you intend to explore ice volcanoes on the Great Lakes, please heed posted regulations and take every safety precaution to avoid hypothermia, injury, and even drowning.