Pillow lavas more than two billion years old indicate large submarine volcanoes existed during the early stages of the Earth's formation.[19] Pelèan eruptions Peléan eruption: 1: ash plume, 2: volcanic ash rain, 3: lava dome, 4: volcanic bomb, 5: pyroclastic flow, 6: layers of lava and ash, 7: strata, 8: magma conduit, 9: magma chamber, 10: dike Peléan eruptions are violent eruptions characterized by fast-moving streams of hot volcanic gas and rock called pyroclastic flows or nuées ardentes.[23] Named for the stratovolcano Mount Pelée on the island of Martinique in the Caribbean Sea, Peléan eruptions occur when thick magma, typically of rhyolite, dacite and andesite type, is involved, and share some similarities with another type of explosive eruption known as Vulcanian eruptions.[23] The thick magma associated with Peléan eruptions can form lava domes and lava spines in the volcano's vent or on the volcano's summit.[23] Lava domes are steep-sided lava masses frequently circular in plan view and spiny, rounded, or flat on top.[24] If a lava dome is created, it may later collapse, forming an ash column and sending flows of ash and hot volcanic blocks down the volcano's flanks.[23] Lava spines are upright cylindrical masses of lava caused by the upward squeezing of pasty lava inside a volcanic vent.[22] Plinian eruptions Plinian eruption: 1: ash plume, 2: magma conduit, 3: volcanic ash rain, 4: layers of lava and ash, 5: stratum, 6: magma chamber Plinian eruptions are large explosive eruptions that form pyroclastic flows and enormous dark columns of tephra and gas that commonly rise into the second layer of the Earth's atmosphere.[23][26] Named for Roman natural philosopher Pliny the Younger, these spectacularly explosive eruptions are associated with magmas of high viscosity and gas content such as dacite and rhyolite and typically occur at calderas and stratovolcanoes.[27] The duration of these eruptions is highly variable, ranging from hours to days, and they commonly occur at volcanic arcs where the Earth's tectonic plates are moving towards one another, with one sliding underneath the other called a subduction zone.[27] Although Plinian eruptions typically involve magma with high levels of silica, such as dacite and rhyolite, they can occasionally occur at volcanoes characterized by passive basaltic eruptions, including shield volcanoes, when the magma chambers become differentiated and zoned to create a siliceous top.