 Eruptive fissure on southeast rim of Kilauea caldera, Hawai`i. This eruptive fissure was active briefly during an eruption in July 1974. Note prominent spatter ramparts on right, and subdued rampart on left, built by the ejection of lava along the fissure. The smooth texture of the surface on the lip of the fissure (lower right) is evidence that lava drained back into the fissure toward the end of the 1974 eruption. |
Fissure
In geology, a fissure is a fracture or crack in rock along which there is a distinct separation; fissures are often filled with mineral-bearing materials. On volcanoes, a fissure is an elongate fracture or crack at the surface from which lava erupts. Fissure eruptions typically dwindle to a central vent after a period of hours or days. Occasionally, lava will flow back into the ground by pouring into a crack or an open eruptive fissure, a process called drainback ; sometimes lava will flow back into the same fissure from which it erupted. |
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Mauna Loa Volcano, Hawaii Lava erupts from fissures high on the northeast rift zone of Mauna Loa in the early morning hours of July 6, 1975. These fissures fed several lava flows, the longest of which traveled 5.2 km northward toward Mauna Kea (in background). |
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Mauna Loa Volcano, Hawaii This eruptive fissure broke out on the northeast rift zone of Mauna Loa about 15 hours after the eruption began in the summit caldera, about 15 km uprift (toward upper left). Initially about 1.6 km long, lava fountains along the fissure were soon restricted to six vent areas. These vents built a spatter rampart, a cinder and spatter cone, and a lava shield along the fissure. The most productive vent is in the upper left. |
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Kilauea Volcano, Hawaii Lava fountains rise from two eruptive fissures in the first week of the Pu`u `O`o-Kupaianaha eruption of Kilauea Volcano. The fissures cut through forest and older lava flows on a remote section of the volcano's east rift zone. See eruption summary for a description and additional photographs of this eruption. |
 Drainback on Kilauea Volcano. Lava fountains erupting from a fissure feed an `a`a flow that is pouring into an older crack (lower right) on the east rift zone of Kilauea. |
Drainback Lava will sometimes return to the subsurface by flowing into an open crack, fissure, or active vent, a process called drainback. Drainback is common in the late stages of an eruptive episode on Kilauea and Mauna Loa volcanoes, when lava reverses its normal direction of movement and flows back into the fissure or vent from which it was erupted. |