A Hawaiian eruption is a type

Types of volcanic eruptions

During a volcanic eruption, lava, tephra , and various gases are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed...

 of volcanic eruption where lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaii

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

an 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

Volcanic ash

Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

 is produced. This type of eruption occurs most often at hotspot

Hotspot (geology)

The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...

 volcanoes such as Kīlauea

Kilauea

Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...

, though it can occur near subduction zones (e.g. Medicine Lake Volcano

Medicine Lake Volcano

Medicine Lake Volcano is a large shield volcano in northeastern California about northeast of Mount Shasta. The volcano is located in a zone of east-west crustal extension east of the main axis of the Cascade Volcanic Arc and the Cascade Range. The thick shield is from east to west and from...

 in California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

) and rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

 zones. Another example of Hawaiian eruptions occurred on Surtsey

Surtsey

Surtsey is a volcanic island off the southern coast of Iceland. At it is also the southernmost point of Iceland. It was formed in a volcanic eruption which began 130 metres below sea level, and reached the surface on 15 November 1963. The eruption lasted until 5 June 1967, when the island...

 from 1964 to 1967, when molten lava flowed from the crater to the sea.

Hawaiian eruptions may occur along fissure vent

Fissure vent

A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...

s, such as during the eruption of Mauna Loa Volcano in 1950, or at a central vent, such as during the 1959 eruption in Kīlauea Iki

Kilauea Iki

Kīlauea Iki is a pit crater which is next to the main summit caldera of Kīlauea.- Kilauea volcano eruption :In August 1959, a swarm of deep earthquakes was detected by the Hawaiian Volcano Observatory. In October it was indicated by seismographs that Kilauea summit was filling with magma...

 Crater, which created a lava fountain 580 meters (1,900 ft) 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

Rift zone

A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...

 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

Mount Mihara

is an active volcano on the Japanese isle of Izu Ōshima. Although the volcano is predominantly basaltic, major eruptions have occurred at intervals of 100–150 years....

 on Izu Ōshima

Izu Oshima

is a volcanic island in the Izu Islands and administered by the Tokyo Metropolitan government, Japan, lies about 100 km south of Tokyo, 22 km east of the Izu Peninsula and 36 km southwest of Bōsō Peninsula. serves as the local government of the island...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

).

Hawaiian eruptions usually start by formation of a crack in the ground from which a curtain of incandescent magma

Magma

Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 or several closely spaced magma fountains appear. The lava can overflow the fissure and form aā or pāhoehoe style of flows. When such an eruption from a central cone is protracted, it can form lightly sloped shield volcano

Shield volcano

A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...

es, for example Mauna Loa or Skjaldbreiður

Skjaldbreiður

Skjaldbreiður, meaning the broad shield in Icelandic, is an Icelandic mountain from whose name the term "shield volcano" derives. It was formed in a huge and protracted eruption roughly 9,000 years ago...

 in Iceland

Iceland

Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

.

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

Basalt

Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

 in composition. Hawaiian basalts that make up almost all of the islands are tholeiite

Tholeiite

The tholeiitic magma series is one of two main magma series in igneous rocks, the other magma series being the calc–alkaline. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...

. These rocks are similar but not identical to those that are produced at ocean ridges. Basalt relatively richer in sodium and potassium (more alkaline) has erupted at the undersea volcano of Lōihi 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

Nephelinite

Nephelinite is a fine-grained or aphanitic igneous rock made up almost entirely of nepheline and clinopyroxene . If olivine is present, the rock may be classified as an olivine nephelinite. Nephelinite is dark in color and may resemble basalt in hand specimen...

 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 plume

Mantle plume

A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...

s may work.

Safety

Hawaiian eruptions are usually the most attractive to tourists and are the safest because there is little danger from ash. However, Hawaiian eruptions are not always safe.

In 1790, 80 warriors marching on Kīlauea were killed in an eruption. On May 18, 1924, a plantation accountant named Truman Taylor who was sightseeing on Kīlauea's caldera, was hit with debris from an explosion. Although rushed to hospital, Taylor succumbed to his injuries later that day.

External links

• Hawaiian Volcano Observatory