Rejuvenation Stage Volcanoes

As one of the geologic stages in the formation of the Hawaiian Islands, rejuvenation volcanic eruptions formed some of our iconic landforms. Rejuvenation stage volcanoes are the last eruptions to occur after the main shield volcanoes have stopped erupting, and experienced significant erosion, landslides, and coral reef growth. Some of these puʻu (hills) inspired moʻolelo that explain their creation and connection to Hawaiian gods. Learn the traditional names of these famous puʻu in Hawaiʻi.

Kukulu Kahua

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Vocabulary

Craters, Calderas, and Cones

Calderas are craters more than 1.6 km (1 mi) in diameter formed by the collapse of the summit of a shield volcano. Throughout the shield-building, or primary activity stage, the caldera repeatedly settles and fractures as magma withdraws, and refills as magma returns. Haleakalā “crater” on Maui is not a caldera or a crater, but a depression formed by the cutting back and joining of valley head walls by stream erosion.

Volcanic cones are hills built by fragments of lava that fall around a vent. There is usually a crater or depression at the summit of the cone. In Hawai’i, the southwest side of a cone will frequently be higher because northeast trade winds pick up and deposit ash or cinder there as the cone erupts. Cones associated with shield building or primary activity are found along the major rift zones of a volcano. These are still visible on the island of Hawai’i. Many cones associated with secondary activity can be found on Ni’ihau. Kaua‘i, O’ahu and Maui. Secondary activity has also occurred on Kaho’olawe and East Moloka’i. Examples of secondary eruptions include Diamond Head, Koko Head and Punchbowl on O’ahu, Kalaupapa on Moloka’i, the Kilohana Shield on Kaua’i and the cinder cones in Haleakalā, Maui.

Ash and tuff cones farm when hot magma encounters water and the resulting steam explosion causes the lava to break into small particles of volcanic ash— fragments less than .5 cm (.2 in) across. Tuff is formed when volcanic ash fragments become cemented together, often with bits of coral and sand that blew up during the explosion. Ash cones may become tuff cones over time. The explosive eruptions from tuff or ash cones send fragments high into the air. These dispersed fragments tend to pile up in broad cones with wide saucer-shaped craters. Some less explosive tuff cones, such as Koko Crater, are taller and narrower. Since they are the result of hot magma coming in contact with cold water, tuff cones tend to be close to the ocean or former shorelines. On O‘ahu Diamond Head and Koko Head are examples of tuff cones.

Cinder and spatter cones are usually found on higher ground farther from the shoreline. Cinder cones are built of lava cinders, fragments greater than .5 cm (.2 in) across, which are solid when they hit the ground. Spatter cones are farmed by fragments of lava that fall back to the ground in a partly liquid state and spatter when they hit the surface. Cinder and spatter cones are narrower and have smaller craters than ash and tuff cones because their eruptions tend to be less explosive. Cinder cones can be found at the summits of Mauna Kea and Haleakalā. Examples of cinder cones on O’ahu are Pu’u Ualaka’a (Round Top), Pu’u Kākea (Sugarloaf) and Pu’u ‘Ōhi’a (Tantalus) behind Honolulu.

tuff cone drawing from Ohia Project — tuff cone drawing from ʻŌhi‘a Project

cinder cone drawing from Ohia Project — cinder cone drawing from ʻŌhi‘a Project

According to one theory the period of secondary activity that produced these cones extended over several tens of thousands of years and occurred more or Iess at the same time on the main islands. There were also long periods of quiet between periods of eruptions. An alternative theory contends that secondary activity occurred at separate times when a volcano was approximately 150 km (90 mi) beyond the hot spot. On the Ko’olau volcano of O’ahu, this renewed activity appears to have occurred after more than a million years of volcanic quiet on an island 400 km (250 mi) away from the hot spot. Why? Scientists are actively seeking answers to the mystery of secondary activity.

*Scientist now refer to “secondary” activity as “rejuvenation”.

ʻŌhia Project

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