Pit craters, recent fissures and lava flows, and shields dominate the surface of Kilauea's upper east rift zone. The zone extends 11 km from the outermost ring fault of the summit caldera to Napau Crater. The ring fault is located just west of Puhimau Crater, about 3.5 km from the center of the caldera. The upper part of the east rift zone begins at an elevation of 1,100 m above sea level near Puhimau Crater and drops to about 790 m at Napau Crater.

Lava shields. The upper east rift zone consists of two prominent lava shields, Mauna Ulu and Kane Nui o Hamo. Lava flows from the Mauna Ulu eruption in 1969-1971 and 1972-1974 buried two nearby pit craters, `Alo`i and `Alae, and flowed south to the ocean. Kane Nui o Hamo was active more than 700 years ago and produced a flow field comparable in size to that of the Pu`u `O`o-Kupaianaha eruption (about 100 km²).

Spatter and cinder cone. The most prominent spatter and cinder cone in the upper east rift zone is Pu`u Huluhulu. Lava flows from Mauna Ulu partially surround the the base of the cone.

Pit craters. The most conspicuous feature of the upper east rift zone is a series of pit craters with diameters between 20 and 1,600 m. Hi`iaka and Makaopuhi Craters each consist of two craters; Pauahi Crater includes three craters, two of which overlap and a third that is nearly detached from the others. Some pit craters are intersected by eruptive fissures or partly filled by lava flows, and two were completely filled by the Mauna Ulu eruption. Pit craters form by collapse of the ground due to the underground movement of a significant volume of magma. The concentration of pit craters in the upper east rift zone suggests that magma accumulates in shallow pockets beneath this part of the zone, then subsequently moves up or down the rift zone to leave behind a void space. The complex histories of several pit craters, and the coarse ejecta exposed in the walls of at least two of them, indicate that they have long been sites of repeated collapse and, at times, phreatic explosions.

The locations of the larger pit craters coincide generally with a gradual bend in the orientation of the east rift zone between Hi`iaka and Makaopuhi Craters. The uprift segment trends southeast, whereas the downrift segment trends east-northeast. The reason for this curve is uncertain, but  scientists have proposed that the bend is caused by the gradual seaward migration of the axis of the rift zone (see explanation). The complexity of structures in the area of the bend apparently enables pockets of magma to be stored there. Draining of these pockets removes support for the ground above, which then collapses to form a crater.

References

Hazlett, R., 1993,Geological Field Guide, Kilauea Volcano: Hawai`i Natural History Association, 127 p.

Holcomb, R.T., 1986, Eruptive history and long-term behavior of Kilauea Volcano, in Decker, R.W., Wright, T.L., and Stauffer P. H., (eds.), 1987, Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, 1667 p.