Hawai‘i (Big Island)

Volcano Tectonic Style Temperature Kilauea Summit Hot Spot 1170°C Erta` Ale Divergent Plate 1130°C Momotombo Convergent Plate 820°C H20H C S H2H CO H2SH2S HCl HF Long-lasting Eruption of Kilauea Volcano, Hawai`i Leads to Volcanic- Air Pollution

Profile of Hawaiian shield volcanoes compared with the profile of Mount Rainier, one of the larger composite volcanoes of the Cascade Range, drawn at the same scale.

Aerial view of some of the prominent fissures within the southwest rift zone of Kilauea Volcano. The shiny dark lava was erupted from these fissures in September (Photograph by J.D. Griggs.)

Growth profiles of Kilauea's newest volcanic cone, built during the Pu'u 'O'o eruption.

Map of the Big Island showing the volcanic hazards from lava flows. Severity of the hazard increases from zone 9 to zone 1. Shaded areas show land covered by historic flows from three of Hawaii's five volcanoes (Hualalai, Mauna Loa, and Kilauea).

Pahoehoe Flows Dominate Extrusive Igneous Rock - Lava (Hawaii) A’a Lava on top of Pahoehoe Flows Pahoehoe Flows Dominate

Shiny strands of volcanic glass, called Pele's hair (above) are commonly found downwind from active eruptive vents. Volcanic spatter commonly becomes tightly welded to form mounds around active vents (below). (Photographs by Donald W. Peterson and Richard P. Moore, respectively.)

Graph illustrating the difference in average chemical compositions between lava erupted by Hawaiian volcanoes and by Mount St. Helens in The number given for each chemical element gives the amount (in weight percent) of that element (expressed as oxide) contained in the lava. Left: Note the contrast in color and texture between Hawaiian basalt (dark) and Mount St. Helens dacite (light).

The pyroclastic deposits exposed at Kilauea indicate that about two dozen major explosive eruptions have occurred during the past 70,000 years. Mauna Loa apparently has had less frequent explosive eruptions during the same time interval. Judging by their distribution and thickness, Kilauea's prehistoric pyroclastic deposits had to be produced by explosive eruptions at least as powerful as the 1790 eruption and, in some cases, several times stronger.

Kilauea's explosions Map showing areas covered by fallout from 4 explosions at Kilauea. This map is a work in progress, and the question marks indicate areas where more observations are needed

Areas to the right (east) and seaward of the dotted lines are closed due to the potential for major land collapse. Where can we see red lava? Currently, lava is flowing in a remote area of the park, 3 miles beyond the ranger station at the end of Chain of Craters Road:

Methane Gas Explosions Underground explosions occur in front of lava flowing over burning vegetation. Plants burn in methane from soils without oxygen as they are covered by lava, creating methane gas explosions. The gas fills underground lava tubes. When the methane ignites, the ground explodes up to 100 yards/meters in front of the advancing lava flow. Rocks and debris blast in all directions. DO NOT APPROACH LAVA FLOWING THROUGH VEGETATION!

The new land where lava enters the ocean is poised to collapse without warning. The area has been closed to the public. USGS 06/28/2005 When Lava Enters the Sea: Growth & Collapse of Lava Deltas

The island of Hawai'i, known as the Big Island, is the largest in the Hawaiian Chain. Greater than twice the area of the remaining main eight Hawaiian Islands combined, Hawai'i encompasses 10,432 sq km (4028 sq mi). The island was formed from five major volcanoes. The volcano of Mauna Kea is the tallest mountain on Earth, reaching nearly 9 km (5.5 mi) from the seafloor to the summit. Although shorter, Mauna Loa's massive size makes it the largest volcano in the world. Kiluea, long thought to be part of Mauna Loa, is the only currently active subaerial volcano in the Hawaiian Island chain and is home to Pele, the Hawaiian volcano goddess.

Kilauea is a shield volcano that rises approximately 6100 m from the ocean floor and 1239 m above sea level. Its summit area consists of a caldera that is 4 km long and 3.2 km wide. This caldera formed by subsidence when magma was withdrawn from beneath the summit (Stone 1926). The main vent of Kilauea is a collapsed crater in the floor of the summit caldera, called Halemaumau. Until the 1959 eruption, the volcano had erupted about once every 4 years.

Once considered a curiosity, explosions at Kilauea are now recognized as an important type of eruption with significant hazard to people on the ground and in the air. How did this revolution in thinking come about? Deposits of tephra (anything solid exploded by a volcano) known as the Keanakako`i Ash are a familiar sight at Kilauea's summit, particularly southwest of the caldera, where the trade winds often blew ash during eruptions. Geologists thought that the ash formed during eruptions in, or within a few years before, 1790, when people were killed. Some older explosion deposits, such as the Uwekahuna Ash, were known but had not been studied carefully. In the late 1980s, Jocelyn McPhie, an Australian on a Fulbright fellowship at UH-Manoa, studied the Keanakako`i Ash and found two ash beds distributed southeastward, though most of the ash, slave to the trade wind, went southwestward. She had no time to continue her work, but her important discovery set the scene for what was to follow.

Kilauea is capable of exploding debris into the westerly jet stream, which then transports the fallout into areas where people live. Small explosions, more numerous than the larger ones, may be driven by groundwater. They may happen when the floor of Halema`uma`u or of the caldera drops down to about the level of the water table, more than 500 m (1,600 feet) deep. Such a drop would serve as a warning that explosions, dangerous to people in the summit but less so in outlying areas, could occur.

What drives such powerful explosions? Around 1,000-1,200 years ago, the largest explosion brought up rocks several kilometers (miles) from the volcano's depths. This explosion was likely caused by rapid expansion of carbon dioxide bubbles within Kilauea's deep plumbing system. Were the Keanakako`i explosions also driven by CO2? What is the interplay between gas from the magma and steam from groundwater? These and other questions will take time to answer.

Glowing lava flows erupt from vents on the south flank of the Pu‘u ‘O‘o cone. Ongoing collapse of the southwest (left) side of the cone has formed a scallop-shaped scar, revealing red layers of welded spatter (deposited as clots of molten lava) that underlie loose tan-colored cinders (bubble-filled, glassy lava pieces that solidified while still airborne). (USGS photo by Richard Hoblitt, January 2004.)

During the first 3½ years of the eruption, fallout from lava fountains at Pu‘u ‘O‘o built a cinder-and- spatter cone 835 feet (255 m) high, more than twice as high as any other cone on Kilauea’s east rift zone. Cone growth ceased after the activity shifted to Kupaianaha in mid When the eruption returned to Pu‘u ‘O‘o in 1992, lava flows from flank vents built a “shield” against the west flank of the cone (top). In 1993, collapse pits appeared on the west flank of Pu‘u ‘O‘o as subsidence over the flank vents undermined the cone. When the crater floor dropped in January 1997, the weakened flank also failed, leaving the prominent “west gap.” Note growth of the shield (bottom). (USGS photos by Tari Mattox and Christina Heliker.)

Kilauea's south flank is moving seaward at up to three inches per year. This area experienced a magnitude 7.2 earthquake in 1975; it is also where the most spectacular palis (the Hawaiian word for cliffs) are found. The southeast flank of Mauna Loa is also moving seaward, but at a slower rate. This region of Mauna Loa experienced a magnitude 6.7 earthquake in Although these motions are a small fraction of those that occurred during the earthquakes, they indicate that the forces that produced the earthquakes and created the palis are still active.

ERUPTION STATISTICS 1983 TO 2004 Lava flows Area covered: 45.1 square miles (116.9 km 2 ) New land: 560 acres (225 ha) Volume: 0.6 cubic miles (2.6 km 2 ) Thickness along coast: 33 to 115 feet (10-35 m) Coastal highway covered: 8.9 miles (14.3 km) Structures destroyed: 189 Pu‘u ‘O‘o Maximum height, 1987: 835 feet (255 m) Height, February 2004: 595 feet (181 m) Crater size: 820 x 1,312 feet (250 x 400 m)