HAWAII NATURE NOTES
THE PUBLICATION OF THE
NATURALIST DIVISION, HAWAII NATIONAL PARK
AND THE HAWAII NATURAL HISTORY ASSOCIATION

HALEAKALA VOLCANO

Haleakala (the house of the sun) is the big volcanic mountain that forms the western part of the island of Maui. It started its growth as a typical shield volcano like Kilauea and Mauna Loa. Thousands of thin flows of olivine basalt and closely related lavas followed each other in rapid succession, until the shield had been built from the ocean floor to an altitude 8,000 feet above the present sea level. At that stage the frequency of eruption decreased, weathering produced soil layers on the surface of some flows before the succeeding flows buried them, and slow changes in the magma body beneath the volcano produced new rock types. This new group of lavas, known as the Kula volcanic series, consists largely of andesites, with some basalts, and picrite-basalts rich in big crystals of olivine and augite. The andesites were more viscous than the basalts, and formed thicker, more massive flows that are well exposed in the western wall of Haleakala "crater" beneath the observation station and along the Halemau'u trail. Picrite-basalt containing large black crystals of augite forms the surface in the vicinity of the observation station.

PLATE 17. Air view looking westward at the summit of Haleakala Volcano. The head of Kipahulu Valley is in the foreground, and Haleakala Crater is in the background.

Toward the end of the eruption of the Kula lavas volcanic activity decreased greatly in intensity, although it probably did not stop altogether. Erosion was able to more than keep pace with the building of the mountain, and streams cut great canyons into the slopes. Some of these were several thousand feet deep. Two of them, the Koolau and Kaupo canyons, cut far back into the heart of the mountain, and their heads coalesced to form one great central depression divided only by a low narrow ridge separating their drainage areas. This depression, modified by later erosion and volcanic activity, forms the present great "crater" of Haleakala (Plates 7, 17), which thus is erosional, not volcanic, in origin.

PLATE 18. Haleakala Crater from the Observation Station, at the end of the highest road in the Hawaiian Islands, 10,000 feet elevation. 1. Koolau Gap; 2. Hanakauhi Peak; 3. Paliku; to the left, the head of Kipahulu Valley, to the right, Kaupo Gap; 4. Haleakala Peak; 5. Puu Naue; 6. Ka Moa a Pele; 7. Puu o Maui; 8. Kamohoalii; 9. Ka Lua a ka Oo 10. Puu a Pele. The cinder cones were built by eruptions along the rift zone crossing the crater floor. (D. H. Hubbard, NPS).

At a still later time volcanism again increased in intensity, and a series of lavas and cinder cones known as the Hana volcanic series was erupted. Like the Kula rocks before them, the Hana lavas were erupted principally from a line of fissures that crossed the mountain from southwest to northeast. This line of fissures, forming the southwest and northeast rift zones of the volcano, crosses the crater (Plate 18). From the observation station at the crater rim a line of cinder cones and lava vents can be seen extending diagonally across the crater and up the far side (Plate 7). The original floors of the eroded valleys have been deeply buried by the lavas and cinder cones that form the present floor of the crater and of the Koolau and Kaupo gaps (Plate 17). The ridge that formerly separated the heads of the two valleys has largely been buried by the flood of later lavas, but part of it can still be seen projecting southward into the "crater" south-southwest of Hanakauhi Peak. The old lavas in the ridge are cut by many nearly vertical dikes, which are the congealed lava fillings of fissures many of which once fed surface lava flows.

Haleakala is the only volcano in the Hawaiian group, except the island of Hawaii, that has erupted during the last few hundred years. About 1750 lava issued from two vents on the southwest rift, one at an altitude of 575 feet and the other at 1,200 feet, and formed a flow that went into the sea. This fresh flow is crossed by the road that follows the coast line from Makena to Keoneolo, at the head of La Perouse Bay.

PLATE 19. Puu Naue, a fairly recent cinder cone on the floor of Haleakala Crater from the southeast. The conical outline and bowl-shaped crater are typical of fresh cinder cones. Plate 7 shows a view of Puu Naue and neighboring cones from the north. (11th Photo Section, USAC).