Hawaii Volcanoes National Park

Pahoehoe And Aa Lava
Hawaii Volcanoes National Park, Big Island, Hawaii
Hawaii Volcanoes National Park (courtesy, NPS)

During eruptions, lava may assume two different physical forms, with gradations in between. The most common type on the caldera floor is pahoehoe, which has a smooth, billowy, or ropy surface. The product of hot, gassy eruptions, pahoehoe is very fluid as it flows. A'a, the other type of lava, is either formed during cooler eruptions, or, more often, as a pahoehoe flow moves over the ground, it cools very slightly, and loses gas along the way. The lava then becomes more sticky and viscous; it begins to move more slowly and the crust breaks up. An a'a flow will have a clinkery surface, but a solid, dense interior.

In places on the caldera floor, escaping gasses speed up the aging and breakdown of the lava flows. The reddish orange lines that border cracks are evidence of the oxidation of iron in the lava. Over millions of years, the solid, black lava flows become the red soil that is prominent on the older islands. Also noticeable at places where gasses are escaping are crusty white areas, deposits of salts, sulfates, and opaline.

Pioneer Plant Life

The caldera is a good area to see how life returns to lava flows. Seeds blown in by the wind are deposited in cracks and take root. The spores of ferns and the tiny seeds of the 'ohi'a are often the first to gain a  foothold in the shady, damp cracks. The lava is porous arid brittle so roots are able to penetrate the rock easily. These plants, along with other species, are the beginning of future forests. If no new lava flows cover the area, generations of plants will grow, die, and grow again.

Spatter Ramparts

The spatter ramparts on the floor of the central caldera were built by a series of eruptions. At approximately 8:30 a.m. on April 30, 1982, geologists at the Hawaiian Volcano Observatory noted an increase "in the level of seismic activity" being recorded on their seismographs. The activity indicated the possibility of an eruption at the summit of Kilauea. The trails through the caldera, and parts of the Crater Rim Road were closed. At 11:37 a.m., only three hours after the initial burst of seismic warning, a fissure opened on the caldera floor in the same general area of the May 31, 1954 eruption. Hot fluid lavas poured out of a 112-mile-long fissure, and the volcano was in eruption. A crack also opened on the northeast wall of Halema'urna'u and a small outbreak occurred there. Lava fountains sometimes reached heights of 50 to 60 feet above the vents. The erupting lava added to the already existing spatter ramparts, the low lying black "hills" along the trail. Almost one million cubic meters of lava moved across the caldera floor.

During the early morning hours of May 1, the eruption ended. More than 45,000 people came to Kuala during the 19 hours of fiery spectacle.

Parts of the old Halema'uma' to Byron Ledge trail were buried under the April 1982 lava flow. It is particularly important, in the area of that flow, to stay on the marked trail. The lava was very hot and gassy, so a surface that appears to be solid may only be the surface of a lava tube or gas bubble.

Explosive Debris

The ground in the caldera that is covered with rock fragments and debris is pre-1924. The ejecta resulted from the 1924 series of steam explosions. At that time there was a major collapse of the summit and magma came into contact with ground water. Major explosions resulted which continued for two weeks. An eight-ton boulder was thrown out of Halema'uma'u and landed near the road across from the parking lot. A rock fell on a photographer and seriously injured his leg. He died enroute to a hospital from loss of blood, the only known fatality of an eruption since the 1790 steam explosions killed part of a Hawaiian army in the Ka'u Desert.


Traditionally, Halema'uma'u is believed to be the dwelling place of Pele and her family. The ancient people of Hawaii approached the crater with great respect. Times and traditions have changed somewhat, but it is still important for modern day visitors to approach the crater with caution.

From 1823 to 1924, Halema'uma'u contained a lava lake, which continually rose and fell. The 1924 series of explosions disrupted the activity there, and there hasn't been such a prolonged series of eruptions since. The crater of Halema'uma' is considered by many to be the main vent of Kilauea volcano, though eruptions often occur at other places as well. Halema'uma'u is approximately 300 feet deep and 3,000 feet across.

Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication

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