Schematic illustration showing the inferred irregular conduit geometries of (a)

Schematic illustration showing the inferred irregular conduit geometries of (a) Old Faithful geyser, in Yellowstone National Park; (b) Velikan geyser, in Kamchatka, Russia, with boulders at the bottom depicted in brown; and (c) Geysir, in Iceland. The walls of the conduits are lined with white silica sinter similar to that exposed on the surface. From manuscript by Hurwitz and Manga (Annual Review of Earth and Planetary Sciences, 2017. Vol. 45, pp. 31–59).