Ice-marginal volcanism

Ice-marginal volcanism can occur when volcanic vents are adjacent to, rather than beneath, glaciers. It is common in volcanically active regions with steep topography, such as British Columbia's Garibaldi Volcanic Belt. During the waning stages of large-scale glacial events, ice may have retreated from high elevations but still occupy valleys. Thus, when lava erupts from high-altitude vents, it may flow downhill to be impounded against ice. An excellent example of this type of feature is the Barrier, located in Garibaldi Provincial Park, British Columbia.

The diagram to the left shows the sequence of events in the development of an ice-marginal lava flow. Initially, the flow behaves as any subaerial flow, but after reaching the ice, the lava flow front cools rapidly and forms a barrier behind which lava begins to pool, preventing further direct lava-ice contact. This results in an unusually thick flow front. After the ice retreats, the flow front consists of a steep, unstable cliff, which is rapidly broken down by erosion.