thumb|320px|3-D perspective view of the southeastern Hawaiian Islands, with the white summits of [[Mauna Loa ( high) and Mauna Kea ( high)]]

The evolution of Hawaiian volcanoes occurs in several stages of growth and decline. The fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch across the North Pacific Ocean, called the Hawaiian–Emperor seamount chain. Hawaii's volcanoes rise an average of to reach sea level from their base.

Hawaiian islands undergo a systematic pattern of submarine and subaerial growth that is followed by erosion. An island's stage of development reflects its distance from the Hawaii hotspot.

Background

500px|right|The characteristic "V" shape, a separation between the older Emperor and newer Hawaiian sections, is easily visible in this image|thumb

The Hawaiian–Emperor seamount chain is remarkable for its length and its number of volcanoes. The chain is split into two subsections across a break, separating the older Emperor Seamount Chain from the younger Hawaiian Ridge; the V-shaped bend of the chain is easily noticeable on maps. The ratio of magnesium to silica in the lava is a sign of what stage the volcano is in, as over time the volcano's lavas shift from alkalic to tholeiitic lava, and then back to alkalic. Due to stretching forces, the development of two or more rift zones is common. The lava accumulates in a shallow magma storage reservoir.

Because the eruptions occur with the volcano underwater, the form of lava typically erupted is pillow lava. Pillow lava is rounded balls of lava that was given very little time to cool due to immediate exposure to water. Water pressure prevents the lava from exploding upon contact with the cold ocean water, forcing it to simmer and solidify quickly. This stage is thought to last about 200,000 years, but lavas erupted during this stage make up only a tiny fraction of the final volume of the volcano.

The Koʻolau Range and West Maui volcanoes are examples of volcanoes in this stage of development. Note, however, that because in this stage eruptions are very infrequent (occurring thousands or even tens of thousands of years apart), erosion is still the primary factor controlling the volcano's development. After this stage the volcano becomes extinct and never erupts again.

Coral atoll stage

400px|thumb|right|An animated sequence showing the erosion and subsidence of a volcano, and the formation of a [[coral reef around it – eventually resulting in an atoll.]]

Eventually, erosion and subsidence break the volcano down to sea level. At this point, the volcano becomes an atoll, with a ring of coral and sand islands surrounding a lagoon. All the Hawaiian islands west of the Gardner Pinnacles in the Northwestern Hawaiian Islands are in this stage.

Atolls are the product of the growth of tropical marine organisms, so this island type is only found in warm tropical waters. Eventually, the Pacific Plate carries the volcanic atoll into waters too cold for these marine organisms to maintain a coral reef by growth.

See also

  • Geology of the Canary Islands – a group of volcanic islands in the Atlantic Ocean that follow a similar sequence of growth and decline stages
  • List of volcanoes in the Hawaiian – Emperor seamount chain

References

Further reading

  • Volcano Watch – Evolution of Hawaiian Volcanoes