A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very little amount of volcanic ash is produced. This type of eruption occurs most often on hotspot volcanoes such as Kilauea, though it can occur near subduction zones (e.g. Medicine Lake, California.) Hawaiian eruptions are usually the most attractive to tourists and are the safest because there is little danger from ash. Hawaiian eruptions may occur along fissure vents, such as during the eruption of Mauna Loa Volcano in 1950, or at a central vent, such as during the 1959 eruption in Kilauea Iki Crater of Kilauea Volcano, Hawaii, which created a lava fountain 580 meters (1,900 feet) high and formed a 38 meter cone named Puu Puai. In fissure-type eruptions, lava spurts from a fissure on the volcano's rift zone and feeds lava streams that flow downslope. In central-vent eruptions, a fountain of lava can spurt to a height of 300 meters or more (heights of 1600 meters were reported for the 1986 eruption of Mount Mihara on Izu Ōshima, Japan). Hawaiian eruptions usually start by formation of a crack in the ground from which a curtain of incandescent magma or several closely spaced magma fountains appear. The lava can overflow the fissure and form aa or pahoehoe style of flows. Eruptions from a central cone can form small lightly sloped shield volcanoes, for example the Mauna Ulu. When globules of lava are thrown into the air, they are often still fluid when it impacts the ground, flattening into "cow-dung bombs."
Petrology of Hawaiian Basalts
The key factors in generating a Hawaiian eruption are basaltic magma and a low percentage of dissolved water (less than one percent). The lower the water content, the more peaceful is the resulting flow. Almost all lava that comes from Hawaiian volcanoes is basalt in composition. Hawaiian basalts that make up almost all of the islands are tholeiite. These rocks are similar but not identical to those that are produced at ocean ridges. Basalt relative richer in sodium and potassium (more alkaline) has erupted at the undersea volcano of Loihi at the extreme southeastern end of the volcanic chain, and these rocks may be typical of early stages in the "evolution" of all Hawaiian islands. In the late stages of eruption of individual volcanoes, more alkaline basalt also was erupted, and in the very late stages after a period of erosion, rocks of unusual composition such as nephelinite were produced in very small amounts. These variations in magma composition have been investigated in great detail, in part to try to understand how mantle plumes may work.
References
Frankel, Charles (2005). Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io. Cambridge University Press, 21-22. ISBN 0521803934. Frankel, Charles (1996). Volcanoes of the Solar System. Cambridge University Press, 17. ISBN 0521477700. Casadevall, T.J. (ed.) (1995). Volcanic Ash and Aviation Safety: Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety. DIANE Publishing, 437. ISBN 0788116509. MacDonald, Gordon A. (1983). Volcanoes in the Sea: Geology of Hawaii (2nd edition). University of Hawaii Press, 156-157. ISBN 0824808320.
