Volcano Watch — State of Hawai`i geologic map available online

The State's geology is presented on eight full-color map sheets, one for each of the major islands. These map sheets, the illustrative meat of the publication, can be downloaded in pdf format, ready to print. The map's scale is 1:100,000 (1 inch on the map equals about 1.6 miles on the ground), so that each map is about 27 inches by 36 inches. The island of Hawai`i, largest of the islands, is depicted at a smaller scale, 1:250,000 (1 in. = 4 mi), so that it, too, can be shown on 36-inch-wide paper.

The new publication isn't limited strictly to its map depictions. Twenty years have passed since David Clague and Brent Dalrymple published a comprehensive USGS report on the Hawaiian-Emperor volcanic chain that summarized the geology of all the islands, and it has been even longer since Gordon Macdonald's 1970 book, Volcanoes in the Sea (revised in 1983). The new statewide geologic map thus includes a lengthy pamphlet that revisits many of the concepts that have evolved in our geologic understanding of the eight main islands.

The pamphlet includes simplified page-sized geologic maps for each island, summaries of all the ages from samples gathered since about 1960, generalized depictions of geochemical analyses for each volcano's eruptive stages, and discussion of some outstanding topics that remain controversial or warrant additional research. The pamphlet also contains a complete description of map units, which enumerates the characteristics for each of the State's many rock layers shown on the map sheets.

Since the late 1980s, the audience for geologic maps has grown as desktop computers and map-based software have become increasingly powerful. Those who prefer the convenience and access offered by Geographic Information Systems (GIS) can also feast on this publication. An electronic database, suitable for most GIS software applications, is available for downloading. The GIS database is in an Earth projection widely employed throughout the State of Hawai`i, using the North American datum of 1983 and the Universal Transverse Mercator system projection to zone 4.

"This digital statewide map allows engineers, consultants, and scientists from many different fields to take advantage of the geologic database," said John Sinton, a geology professor at the University of Hawai`i, whose new mapping of the Wai`anae Range (West O`ahu) appears on the map. Indeed, when a test version was first made available, most requests came from biologists, archaeologists, and soil scientists interested in applying the map's GIS database to their ongoing investigations.

Another area newly depicted on the map, in addition to the Wai`anae Range, is Haleakalā Volcano, East Maui. Also updated are the boundaries of lava flows on Kīlauea Volcano, Hawai`i Island, where the landscape has continued to evolve in the 10 years since publication of the previous geologic map of the Big Island by Wolfe and Morris in 1996. For the other islands, much of the map is compiled from mapping published in the 1930s-1960s. This reliance stems partly from shortage of funding to undertake entirely new mapping but is warranted by the exemplary mapping of those early experts. The boundaries of all map units are digitized to show correctly on modern topographic maps.

Those unprepared to print the maps themselves will be able to buy the map as a printed product in the future. For now, however, the preliminary version bridges the two-year gap required to edit and print a formal USGS Scientific Investigations map. In this way, scientists, engineers, land-use planners, and anyone interested in the geologic history of Hawai`i can begin using the data and interpretations it contains.

To obtain a copy online, reach for the link on the USGS publications Web site, http://pubs.usgs.gov/ofr/2007/1089. Be advised: a rapid data-transfer connection is helpful, because the explanatory pamphlet (pdf format) is 8 megabytes, and the map sheets (also in pdf) range from 5 to 40 megabytes.

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Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have been elevated above background levels. The summit caldera has been expanding, indicating inflation, since the beginning of 2007. The number of earthquakes located in the summit area increased from typical levels of less than 10 per day to nearly 20 per day on May 12. The earthquakes were concentrated in the upper southwest and east rift zones. A magnitude-4.7 earthquake, along with a number of aftershocks, occurred on the morning of May 24.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from vents within the eastern half of the crater. Lava continues to flow through the upper portion of the PKK lava tube to where the Campout tube branches off about 1 km south of Pu`u `O`o. A new breakout from this section of the PKK tube has been sending lava down-slope onto the upper flow field for the last few weeks. This breakout is upslope from the Campout tube branch and may be the start of a new tube system.

Though the new breakout is robbing part of the lava supply, the Campout tube continues to carry lava downslope, where it is feeding breakouts on the coastal plain near the base of the Royal Gardens subdivision, and possibly inland from East Lae`apuki. The lava ponding near the base of Royal Gardens, ongoing for the last several months, finally advanced across the coastal plain and reached the ocean at Poupou on May 16. This new ocean entry continues to be active, though the entry has not yet become well established. It is located within Hawai`i Volcanoes National Park. To the west, the Kamokuna entry, fed by the main branch of the Campout tube, appears to no longer be active.

Access to the sea cliff at the ocean entries is closed, due to significant hazards. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

Seven earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.0 earthquake occurred at 1:02 a.m. H.s.t. on Thursday, May 17, and was located 5 km (3 miles) west of Kīlauea summit at a depth of 6 km (4 miles). A magnitude-2.0 earthquake occurred at 5:17 p.m. later that day and was located 1 km (1 mile) northeast of Captain Cook at a depth of 12 km (8 miles). A magnitude-3.3 earthquake occurred at 5:59 a.m. on Friday, May 18, and was located 3 km (2 miles) northwest of Pahala at a depth of 6 km (4 miles). A magnitude-2.2 earthquake occurred at 11:36 a.m. on Monday, May 21, and was located 4 km (2 miles) northwest of Captain Cook at a depth of 12 km (7 miles). A magnitude-4.7 earthquake occurred at 9:13 a.m. on Thursday, May 24, and was located 3 km southeast of Kīlauea summit at a depth of 2 km (1 mile). A magnitude 4.1 aftershock occurred 20 minutes later at 9:33 a.m. and was located 5 km (3 miles) southeast of Kīlauea summit at a depth of 4 km (2 miles). A magnitude-3.9 aftershock occurred at 10:51 a.m. on Thursday and was located 6 km (4 miles) southeast of Kīlauea summit at a depth of 1 km (1 mile).

Mauna Loa is not erupting. Two earthquakes were located beneath the summit. Extension of distances between locations spanning the summit, indicating inflation, continues at steady, slow rates.