# Volcano Watch — Geologic Map of Hawaii Island available in electronic format

Release Date:

The U.S. Geological Survey recently made available the digital geologic map for the Island of Hawaii. Compiled by Frank Trusdell of the Hawaiian Volcano Observatory, this map is the electronic equivalent of a printed map that first appeared in 1996.

Geologic map of the Island of Hawaii

(Public domain.)

The 1996 full-color map by Edward Wolfe and Jean Morris shows the numerous lava-flow layers, vents, and earthquake faults of the Big Island. The paper map has already gone through two printings, owing to its popularity among visitors to Hawaii Volcanoes National Park and in bookstores in Hilo.

The digital version is made for computer-based applications, using Geographic Information Systems (GIS) software. It allows a user to quickly gather information not readily available from the paper version. For example, the area covered by all lava flows younger than 200 years in age can be determined by a few keystrokes. In the not-so-olden days, an analyst would laboriously trace each outline with a planimeter to obtain the areas, spending a day or a week in the process to gather the same information.

GIS analysis, however, offers far greater advantage than determining the size or shape of geological things. It allows numerous kinds of information to be superimposed. For civil-defense purposes, the relation of roads and utilities to young vents is readily determined. A biologist might compare his or her information about bird nesting sites with the age or type of lava (aa or pahoehoe), thereby finding a new correlation that might lead to enhanced management of Hawaii's natural resources.

Archaeologists have plotted the position of ancestral homesites and heiau (temples) on digital versions of island geologic maps for Kohala and Haleakalā volcanoes, leading to insights about the shrewd use of land by early Polynesians as they experimented with agriculture in their newly found Hawaiian island homes. The power of GIS is limited only by our ability to phrase questions judiciously.

Given the advantage offered by digitized electronic maps, why aren't they always made available in that format, from the get-go? The answer is simple: now they are. The Geological Survey requires digital version of all published maps, in order to increase the usefulness of its products.

The problem has been catching up with vintage maps produced prior to the widespread use of GIS technology. The most important of the older maps will be brought into the electronic age sooner than others, but the task requires diligence and hard work. That's Trusdell's contribution-a gigantic boost for those involved in private- and public-sector work along the island chain.

If you choose to visit the USGS publication page, here's how to do it and what you'll find. You're looking for a product entitled "Digital Database of the Geologic Map of the Island of Hawaii"

The meat of the electronic publication is GIS-based files in a format that can be used by many kinds of software. But PDF versions for some of the files are available, too, as small and intermediate-scale images of the geologic map and explanatory text. Those readers not inclined toward the GIS aspect might find these latter files a useful source of information.

One of the PDF files shows the geologic map draped over a shaded-relief topographic base. By using the clip-and-paste power of a computer, it's possible to capture small areas that will fit on a printed page. But be forewarned; some of the files are probably too large for dial-up connections.

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### Volcano Activity Update

Activity at the summit of Kīlauea Volcano has returned to low levels this past week. The number of earthquakes in the summit area has decreased. Inflation of the summit caldera continues but at a noticeably slower rate than over the past two months.

Eruptive activity at Puu Oo continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source on the flank of Puu Oo to the ocean, with occasional surface flows breaking out of the tube. In the past week, surface flows were active on the coastal plain below Paliuli, 0.6 km (0.4 mi) inland of the coast at Kamoamoa, about 5.5 km (3.4 mi) from the end of Chain of Craters Road.

As of March 23, lava is entering the ocean at East Laeapuki, in Hawaii Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 1,100 m (3,600 ft) long by 250 m (820 ft) wide. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. 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.

There were two earthquakes beneath Hawaii Island reported felt within the past week. A magnitude-3.1 earthquake occurred on Friday, March 17, at 8:10 p.m. and was located 3 km (2 miles) south of Kīlauea summit at a depth of 3 km (2 miles). A magnitude-3.4 earthquake occurred on Wednesday, March 22, at 4:38 a.m. and was located 5 km (3 miles) southwest of Waimea at a depth of 16 km (10 miles).

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit. Inflation continues, but at a rate that has slowed since early October 2005.