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

KILAUEA, HOME OF PELE, THE FIRE GODDESS

DESCRIPTION. Kilauea also is a shield volcano, closely resembling Mauna Loa in its structure, built against the side of its larger neighbor. Small compared to Mauna Loa, Kilauea is no pygmy. Its summit stands some 20,000 feet above the surrounding ocean floor. Kilauea has been built largely by eruptions from two rift zones, extending eastward and southwestward from the summit caldera. The rifts are marked at the surface by many cinder and spatter cones, pit craters, and open fissures. The Chain of Craters road passes close to several of the pit craters on the east rift zone, and cuts through the edge of a small cinder cone revealing its internal structure. Noteworthy among the fissures on the southwest rift are the Great Crack, continuous for more than 10 miles, from which issued the 1823 lava flow of Kilauea; and the large fissures crossed by the road at the southwestern edge of the caldera.

The summit caldera ("crater") of Kilauea is 2-1/2 miles long and 2 miles wide, and its floor has an area of approximately 2,600 acres. At its north eastern edge, below the Volcano House, and at its western edge, below the Uwekahuna overlook, the wall of the caldera consists of a series of steplike fault blocks (Plate 14). Just north of Uwekahuna the boundary cliff is about 400 feet high. The entire floor of the caldera, except for a narrow peninsula projecting from the southeastern side, is made up of new lava flows erupted within the last century. (See Figure 4.) Near its southwestern edge the caldera floor is indented by the depression Halemaumau, the "Fire Pit," a collapsed crater about 750 feet deep. Halemaumau is the focus of Kilauea's eruptive activity and the traditional home of Pele, the Hawaiian goddess of volcanoes.

PLATE 15. Lava lake in Halemaumau, showing islands of semisolid epimagma in the fluid pyromagman, September 9, 1920. (T. A. Jaggar, HVO).

The pit craters along the rift zones are formed by collapse caused by removal of support. Some of the smaller ones may be formed by draining of large lava tubes underneath, with resulting collapse of the overlying rock material into the tube. The larger ones, such as Makaopuhi Crater at the end of Chain of Craters road, probably form above pluglike bodies of magma that work their way upward along the rift zone. Partial withdrawal of the magma causes the unsupported mass of rock above to sink in.

Many fault scarps can be seen on Kilaueae. The walls of the great caldera are themselves fault scarps left by the down-sinking of the floor. Along the rift zones elongate blocks of rock known as grabens have sunk down between two parallel faults, leaving infacing fault scarps at their edges. Along the southern coast Hilina Pali and its associated cliffs are scarps marking faults along which portions of the mountain have slid downward and outward toward the ocean.

Kilauea differs from Mauna Loa in two principal respects, both minor matters volcanologically. One is the greater amount of explosive debris in the vicinity of the caldera. The other is the lava lake activity that existed for many years in the caldera (Figure 6). The explosive debris around Kilauea caldera is of two types. One consists largely or entirely of fragments of glass—the quickly frozen spray of lava fountains. Deposits of this type of material are buff to yellow in color, and generally sandy in texture. They are well exposed in road cuts, fault scarps, and walls of cracks around the southern and southwestern edges of the caldera. In the same area a thin layer of pumice fragments lies on the ground surface. The pumice is the frozen froth of lava fountains that played in the caldera early in the 19th century.

FIGURE 4. Maps and cross-sections of Kilauea caldera in 1825 (after Malden) (A), and in 1949 (B). Note that the large central pit of 1825 has been entirely filled with new lava. The structure beneath the caldera is hypothetical. (From Stearns and Macdonald, 1946). (click on image for an enlargement in a new window)

The second type of explosive debris consists largely or entirely of stony fragments of older lavas, ranging in size from dust to blocks several feet across, broken up and thrown out by violent steam explosions such as those of 1924 described later. Two such periods of steam explosions have occurred during recent times, one about 1790 and the other in 1924. Debris thrown out in 1790 covers the ground surface in the vicinity of the Uwekahuna overlook. Material from the explosions in 1924 forms the surface around Halemaumau, and is abundant near the parking area. One block weighing about 8 tons was thrown 1,000 feet east of the present parking area and 3,000 feet from the center of Halemaumau. A still larger block, weighing about 14 tons, formerly lay near the rim of Halemaumau just north of the lookout platform, but fell back into the pit during a collapse of part of the rim.

A special type of explosive debris is the black sand that comprises the beaches near Kalapana and at some other localities. Where aa lava flows into the sea the contact of the hot lava with sea water causes steam explosions that throw up droplets and fragments of the hot lava. The droplets of still molten lava are quickly chilled to a black or dark brown glass. The debris from the explosions accumulates to form one or more small hills at the edge of the water. These hills are attacked by the ocean waves and soon eroded away. Of three such hills formed by the 1840 lava flow of Kilauea, one is already completely removed. The sand-size fragments, moved along the shore by the waves and currents, accumulate at favorable places to form beaches of black glass sand.

Table 3 lists the historic lava flows of Kilaueae. Comparison with Table 2 indicates that during the historic period activity has been concentrated in the caldera to a much greater degree than has that of Mauna Loa. The table ignores the long periods of constant lava lake activity at Kilauea, except when overflows of the lake produced noteworthy lava flows on the caldera floor. Undoubtedly many more of the latter occurred then are shown, especially during the early part of the historical period when records of the activity were poor.

TABLE 3—Eruptions of Kilauea¹