Kilauea`s lower east rift zone is marked by many young volcanic featuresfissures and cones, lava flows, and ground cracks. The area is also the site of many commercial activities, including residential developments, farms, and cinder-mining and geothermal-power operations. The lower east rift zone extends 23 km from the Heiheiahulu shield to Cape Kumukahi, dropping from an elevation of 520 m to sea level. It is the most populated part of the volcano, one of the fastest growing areas in the state, and the site of at least 111 separate eruptions during the past 1,500 years. Lava flows from those eruptions paved virtually the entire lower east rift zone by adding 4.5 to 6 km3 of lava to the area. The most recent eruptions in the lower east rift zone occurred in 1955 and 1960.
The crest of the lower east rift zone rises 50 to 150 m above the adjoining terrain and is marked by low spatter ramparts and cones as high as 60 m. The lava flows typically spread from a vent along the rift zone toward the northeast or southeast, depending on vent location relative to the topographic crest of the zone. The axis of the rift zone is 3-4 km wide, and several subdivisions sit astride the crest, including Leilani and Nanawale Estates.
Heiheiahulu is the only shield along the lower east rift zone; it marks the boundary between the middle and lower segments of the east rift zone. The shield erupted an estimated 0.4 km3 of lava, sending many flows 5 km south to the ocean. Early episodes of the eruption formed spatter ramparts along a 3.5-km-long fissure.
Pyroclastic deposits when lava mixes with water
Scientists have recognized the deposits from two series of explosive eruptions in the lower east rift zone that resulted from the interaction of magma with shallow groundwater. The oldest deposit is associated with activity just before the collapse of Pu`ulena Crater. Rock fragments were exploded over an area of more than 4 km2. The youngest deposits are those associated with the eruption of Kapoho Crater between about 250 and 400 years ago; violent explosions caused by the interaction with seawater threw glassy lava fragments over an area of about 6 km2.
A future explosive eruption similar to these would be potentially life-threatening and may be difficult to predict. As shown by the 1960 eruption in the village of Kapoho (left), some water-driven explosions should be expected when magma intrudes into the lower east rift zone between Pu`ulena and Kapoho Craters because of the shallow ground-water and perched water tables in the area. Click on image to learn more about the 1960 activity.
Frequency of recent eruptions. The frequency of eruptive activity and the increasing population in the lower east rift zone make it almost certain that future eruptions will affect many more people than ever before. The oldest flow found on the surface erupted 2,400 years agoevery other place in the lower east rift zone has been covered by at least one lava flow since then. Between 1,500 and 200 years ago, the average interval between eruptions was about 12.4 years; between 1790 and 1961, the time interval between eruptions was 42.8 years. Clearly, the eruption rate on the lower east rift zone is not constant. Eruptions are infrequent during periods of frequent summit activity. Most recently, in 1960, many farms and structures in Kapoho village were covered by lava. All residents were evacuated in time (see 1960 eruption summary).
Intrusions. In addition to the eruptions that created new cones or sent lava flows pouring across the ground, scientists have found evidence for many intrusions of magma in the lower east rift zone. These hidden magma bodies can be located with geophysical methods. Measurements suggest that three hot, intrusive bodies underlie Heiheiahulu, Pu`u Kali`u and Pu`u Honua`ula. Scientists assume that intrusions in the lower east rift zone are about as frequent as eruptions.
Hazlett, R. W., 1993, Geological Field Guide Kilauea Volcano: Hawai`i Natural History Association, 123 p.