# Widespread Secondary Volcanism around Kauai

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The University of Hawaii (UH) research ship Kilo Moana returned recently from a four-week expedition mapping and sampling the sea floor around the islands of Kauai, Niihau Kaula, and Middle Bank (located just outside of the new Papahanaumokuakea National Marine Monument).

Pillow lava sample that will be displayed at the UH Manoa Museum.

(Public domain.)

There were two goals of the expedition: (1) to map and sample volcanoes formed by secondary Hawaiian volcanism around the northern Hawaiian Islands and (2) to evaluate the origin of large, broad features north and south of Kauai that were once thought to have formed from giant landslides, like the Nu'uanu slide off Oahu.

The primary features of a Hawaiian shield volcano develop over about 1.5 million years while the volcano is over the hotspot. Secondary volcanism occurs well after the shield-building phase and after the volcano moves away from the hotspot. Honolulu's Diamond Head is the classic example of secondary volcanism. It formed more than 1.5 million years after the end of shield volcanism on Oahu.

The sea floor around the Northern Hawaiian Islands was the focus of the submarine study, because Kauai and the adjoining area has produced more secondary lavas over a longer period of time (about 2.5 million years) than any other island.

The National Science Foundation is sponsoring this study to understand why there is a second period of volcanism in Hawaii and many other oceanic islands, such as Samoa, Society, Kerguelen, and the Austral islands. The project attempts to determine the location, ages, and chemical compositions of secondary volcanism to help determine the cause of this later volcanic activity.

The expedition accomplished a number of tasks, including bathymetric mapping around the northeast portion of the State, sampling submarine flows and vents, and interacting with school kids in near real-time. The scientists shared their on-board experiences virtually with all public schools on Kauai and the public through daily updates on the progress of the expedition and answered questions via the University of Hawaii website. The outreach program will continue on Kauai with teacher training workshops and public science demonstrations.

The expedition succeeded in mapping 17,000 square miles of the sea floor, which is approximately 50 percent larger than the total area of the State of Hawaii. In addition, they discovered many previously unknown small volcanoes around Kauai, Niihau, Kaula and Middle Bank. Scientists collected over a ton of lava and sedimentary rocks using JASON2, a robotic submarine.

Prior to this expedition, the sea floor had been poorly mapped, although it offered great potential for new discoveries. Expectations of finding submarine secondary volcanoes were greatly exceeded during the expedition. The new sea floor mapping shows that it is still possible to make discoveries about the nature of the ocean floor, even in well-traveled areas like Hawaii.

Moreover, secondary volcanism is significantly more widespread and voluminous than previously thought. The origin of this widespread volcanism is not adequately explained by existing models and requires major revisions to our overall understanding of the source and cause of secondary volcanism and how volcanism on the Hawaiian Islands evolves with time.

An international team of scientists from the U.S., Canada, Belgium, and Japan are participating in this study. New maps of the sea floor around the Hawaiian Islands will be produced and made available to the public at the UH School of Ocean, Earth Sciences and Technology (SOEST) Web site.

The team's geochemists will measure the chemical compositions, and the geochronologists will determine eruption ages for the new lava samples. The chemical and age information will be used to develop new models to explain the cause of secondary volcanism in Hawaii and on other oceanic islands in order to better understand how the Earth works.

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### Volcano Activity Update

Kīlauea summit and Puu Oo continued to deflate. Seismic tremor levels increased slightly but are still at low levels. Earthquakes were located mostly beneath Halemaumau Crater and the south flank faults.

The July 21 eruption continues to supply lava from eruptive fissure D, 2.3 km (1.4 mi) northeast of Puu Oo. For the last several months this lava was directed entirely into a perched channel, consisting of separate pools separated by bridges of cooled lava. At dawn on November 21, lava began to erupt directly from fissure D, outside of the perched channel. Lava supply to the perched channel appears to have been mostly redirected through this new outlet, dropping lava levels in the perched channel and cutting off supply to the eastward tube, which had been feeding flows in the vicinity of Puu Kiai.

The new outlet over fissure D initially fed lava flows directed southeast, along the south flank of Kupaianaha, that reached about 1.4 km (0.9 mi) from the eruptive vent. For the last several days, however, the erupted lava has stayed fairly close to the breakout point, with short flows spreading radially away from the vent. These flows have built a new lava shield over fissure D. As the level of the shield has built up, the lava level in the older perched lava channel has also risen back up, showing that the perched channel is still connected to the new breakout point. The result is rejuvenated overflows and seep-fed flows from the old perched channel. To make matters even more confusing, Webcam images suggest that the new breakout point is also beginning to build a perched channel.

At Puu Oo, no incandescence has been seen on the Webcam at night since August. The heavy fume coming from Puu Oo completely obscures any view into the crater. As in years past, Puu Oo likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially enroute to the erupting fissure. Sloughing of Puu Oo into its own crater since late August has left numerous fresh cracks on the north rim and south flank of the cone.

Vent areas are hazardous. Access to the eruption site, in the Puu Kahaualea Natural Area Reserve, is closed (http://www.state.hi.us/dlnr/chair/pio/HtmlNR/07-N076.htm).

One earthquake beneath Hawaii Island was reported felt within the past week. A magnitude-1.7 earthquake occurred at 6:53 p.m. H.s.t. on Saturday, November 24, 2007, and was located 12 km (7 miles) southeast of Waimea at a depth of 22 km (14 miles).

Mauna Loa is not erupting. No earthquakes were located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates.