As lava erupts under a large glacier, the heat of the lava would immediately start to melt the overlying glacial ice to produce meltwater.[12] The resulting meltwater would quickly harden the lava to produce pillow-shaped masses called pillow lava.[12] In places, the pillow lava will fracture to create other types of volcanic deposits called pillow breccia, tuff breccia, and hyaloclastite.[12] If magma intruded and melted a vertical pipe through the overlying glacier, the partially molten mass would cool as a large block with gravity flattening its upper surface to form a flat-topped, steep-sided subglacial volcano called a tuya.[12] The term tuya originates from Tuya Butte in far northern British Columbia.[12] While still in graduate school in 1947, Canadian geologist William Henry Mathews coined the term "tuya" to refer to these distinctive volcanic formations and was one of the first people on Earth to describe in detail these types of subglacial volcanoes.[12] Tuya Butte is the first such landform analyzed in the geological literature, and its name has since become standard worldwide among volcanologists in referring to and writing about tuyas.[12][16] Other subglacial volcanoes, including subglacial mounds, are formed when the erupted magma is not hot enough to melt through the overlying glacial ice.[12] Once the glaciers melt away, the tuyas and subglacial mounds would reappear with a distinctive shape as a result of their confinement within glacial ice.[12] Because volcanic activity in Western and Northern Canada was contemporaneous with the ebb and flow of past glaciations, other volcanoes display ice-contact features.