# Volcano Watch — Scientists explore Mauna Loa's submarine flanks

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Last month, some readers may have noticed a ship cruising back and forth off South Point and the South Kona districts of the Island of Hawaii.

Using an oceanographic research vessel, scientists from the Universities of Hawaii, Massachusetts, and British Columbia, and from France and Australia, teamed up with colleagues from Woods Hole Oceanographic Institution and the U.S. Geological Survey to look at Mauna Loa's submarine flanks. The ship was the modern, fully equipped research vessel Thomas G. Thompson, stationed at the University of Washington in Seattle. The funding for this oceanic expedition came from the National Science Foundation.

This ship was equipped with a high-resolution bathymetric mapper and Jason II, a remotely operated vehicle (ROV). The bathymetric mapper has the ability to image features on the sea floor the size of a house. Previous attempts to map the bottom resulted in maps that were, at best, able to resolve features the size of a football field.

Jason II is a new generation ROV; its predecessor was used to help find the Titanic. This ROV is equipped with three cameras that provide real-time video to a control van located on the deck of the ship. Pilots in this van control the movement of the ship and the ROV. In addition, the ROV has mechanical arms that allow scientists to collect samples in the ocean's depths.

The oceanic expedition is part of a continuing effort to study the submarine flanks of Mauna Loa. Some researchers are interested in studying the Hawaiian hotspot and the upper mantle; others hope to find clues to the volcano's plumbing system, and still others hope to see how Hawaiian volcanoes grow and evolve from submarine to island volcanoes. The oldest section of the volcano is located below sea level. In order to get a better handle on long-term processes, such as geochemical evolution and the growth of volcanoes, we need to go to the submarine environment.

Scientists focused on two geographic areas: the submarine extension of the southwest rift zone, located off South Point, and the west flank of the volcano, between Milolii and Kealakekua Bay. Mauna Loa's southwest rift zone extends for an additional 33 km (20 miles) underwater. Scientists using the ROV were able to sample an accumulation of lava flows over 1.6 km (1 mile) thick in the submarine extension of the Kahuku Pali. This thickness represents about 400,000 years of the volcano's history.

By collecting samples and analyzing them, researchers can learn about the Hawaiian hotspot, the mantle--a region where magma is produced, the internal structure of the volcano or its plumbing system, and about types of eruptions and eruption temperatures.

The west flank of Mauna Loa was the other focal point of the expedition. During the course of surveying with the high-resolution bathymetric mapper, we found several volcanic vents off Kealakekua Bay. USGS scientists were aware of a radial vent eruption that occurred in Kealakekua Bay in 1877 and were able to map out not only the 1877 flows from that eruption but also 11 additional radial vents that were discovered while surveying the terrain. The ROV was used to collect samples and photograph these vents and their flows.

Preliminary results include producing a new high-resolution map of the sea floor from Kealakekua Bay to South Point. This includes the entire 33 km-long (20 mile-long) underwater section of Mauna Loa's southwest rift zone. In all, the map covers about 2,100 km2 (800 square miles) to a depth of 4.5 km (2.8 miles). In addition to discovering the additional radial vents on the west flank, researchers collected over 200 samples to be analyzed and studied. The research vessel is now off on another oceanographic expedition, while the scientists from this one are busy clarifying and comprehending how Hawaiian volcanoes work.

### Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated at the Puu Oo vent during the past week. Lava flows through a tube system from the vent to the sea. Lava continues to enter the ocean at the Wilipea and West Highcastle lava deltas. Ocean entries continue in the area between Highcastle and Lae'apuki, fed by an arm of the Mother?s Day flow with numerous surface breakouts from the base of Paliuli to the coast. Other breakouts light the sky above Pulama pali.

The Wilipea delta had a dangerous collapse on Sunday, December 8, losing 18.5 acres to the sea in just a few minutes. West Highcastle dropped 8.4 acres in another large collapse sometime between Sunday and Monday mornings. These collapses remind the public that the ocean entry areas are extremely hazardous; they can collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary onto the lava deltas and benches.

Four earthquakes were felt during the week ending on December 19. Two were on December 12; one, felt in Honaunau Mauka at 4:41 PM, had a magnitude of 2.4 and was located 2 miles west-southwest of Honaunau at a depth of about 10 miles. The other, a magnitude 3.7 shock felt from Kapulena to Kealia and at Hilo, occurred at 5:17 PM; it was located 4 miles south-southeast of Hualalai summit at a depth of 15 miles. The largest earthquake of the week, a magnitude 3.8, took place at 7:31 on December 14 and was felt across much of the island and Maui; it occurred 12 miles west of Kailua at a depth of 28 miles. The fourth felt earthquake took place at 11:40 PM 3 miles south-southwest of Kapoho at a depth of 1.5 miles; it had a magnitude of 2.3 and was felt in Lani Puna Gardens and Leilani Estates.

Mauna Loa is not erupting. The summit region continues to inflate. The earthquake activity is low with only 3 earthquakes located in the summit area during the last seven days.