# Volcano Watch — New colored map shows sea-floor features in Hawaii

November 26, 2003

A stunning colored map of Hawaii, stretching from Niihau to the Big Island, has just been published. This map is different from most others, because it shows the topography of the sea floor as well as of the islands. It measures 63.5 by 96.5 cm (25 by 28 inches) and is printed on heavy poster paper, suitable for hanging and display.

The map is definitely a “keeper.”

All prominent geologic features of the sea floor, including landslides, seamounts, fracture zones, and volcanic fields are portrayed in color and illuminated from the northeast to show sea-floor relief. All named features are indicated in easy-to-read lettering.

The map is the result of cooperation among the U.S. Geological Survey, the Japan Marine Science and Technology Center (JAMSTEC), the University of Hawaii, and the Monterey Bay Aquarium and Research Institute (MBARI). JAMSTEC funded and led a four-year collaborative survey of the sea floor, utilizing manned and unmanned submersibles, rock dredges, and sediment piston cores to sample and observe the sea floor at specific sites. Ship-based sonar systems were used to map the bathymetry from the sea surface.

The survey data collected by JAMSTEC were used for the bathymetry, augmented by data from other sources. One of these other sources is the bathymetry predicted from variations in sea-surface height, observable from satellites. The shallower the sea floor, the lower the level of the sea surface, owing to the gravitational attraction of the rock. This kind of information provides the low-resolution bathymetry between ship tracks.

The depth to the sea floor is portrayed by color shading. The topography of the islands is in shades of gray. All lava flows erupted since written records were kept are shown in red; all of these flows came from Hualalai, Mauna Loa, and Kīlauea Volcanoes. The map is up to date through summer 2003.

A viewer of the map is immediately impressed with how “busy” the sea floor is next to the islands. Fields of blocky debris indicate the presence of underwater landslides that peeled off the volcanoes in the past, most recently about 100,000 years ago from part of the Kona coast.

The largest such slide, the Nuuanu, broke off the Koolau Range on Oahu and is clearly shown on the map, extending for some 200 km (120 miles) from the Pali. The Nuuanu Slide is joined by the Wailau Slide, which carried away the north side of Molokai before Kalaupapa was formed.

Another prominent slide, little known but striking on the map, is the South Kauai Slide, which reaches almost 100 km (60 miles) southeastward from the island.

Surrounding most of the islands are prominent submerged terraces, shown in orange and yellow) that reflect the sinking of the islands. Oahu and the Maui Nui complex (Maui, Molokai, Lanai, Kahoolawe, and Penguin Bank) all show such terraces.

Submarine rift zones, the sites of past and, in Kīlauea’s case, future eruptions, are immediately apparent on the map. The most striking is the broad Hana Ridge, which reaches 130 km (nearly 80 miles) east from Hana and ends at a depth of 5,000 m (16,000 feet) with two curious, sharp ridges that resemble a gaping, Pac-Man-like mouth. The two other submarine rift zones, the Hilo Ridge from Kohala Volcano and the Puna Ridge from Kīlauea Volcano, pale by comparison with the Hana Ridge.

Not related to Hawaiian volcanism but among the most obvious features of the map are large seamounts that probably are about 100,000 years old, give or take. These large mountains formed by underwater volcanic activity at the East Pacific Rise and drifted along with the Pacific Plate to their present locations. Some of these peaks are some 4,000 m (13,000 feet) high.

The new map was compiled by Barry Eakins, a postdoctoral fellow with the USGS in Menlo Park, CA. Joel Robinson, also of the USGS, greatly aided in the preparation, as did John Smith of UH Manoa and Dave Clague of MBARI (once Scientist-in-Charge of HVO).

The map will be sold for \$7.95 by the Hawaii Natural History Association at Kīlauea Visitor Center and Jaggar Museum. It is also available for downloading on the Internet at http://geopubs.wr.usgs.gov/i-map/i2809. It would make a great Christmas present.

### Volcano Activity Update

Eruptive activity at the Puu Oo vent of Kīlauea Volcano continued unabated during the past week. Low spatter fountaining from the West Gap Pit section of the cone has produced multiple short pahoehoe lobes spreading down the west shield. Breaches in the tube system and the rootless shields near the top of the Mother's Day flow supply small flows in the area. No lava is on Pulama pali or the coastal flat below Paliuli. No lava is entering the ocean.

No earthquakes were reported felt in the week ending on November 26.

Mauna Loa is not erupting. The summit region continues to inflate. Seismic activity remains very low, with only one earthquake located in the summit area during the last seven days. Visit our website (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time earthquake information.