Photograph by S.R. Brantley on
14 August 1998
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.
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.