2 geologists complete new Saipan geologic map

Two geologists from the U.S. Geological Survey have completed the new Saipan bedrock geologic map, the latest one of which was made by the USGS back in 1956.

William “Bill” C. Burton and David Weary, who are based in Reston, Virginia, informed Saipan Tribune over the weekend through emails that the revised and updated Saipan geologic map is now online at http://pubs.usgs.gov/of/2011/1234/.

Burton and Weary conducted the mapping on Saipan for several weeks in the springs of 2006 and 2007.

Burton said that perhaps the most significant result of their new study was the mapping of an extensive network of faults that extend the length of the island.

“These faults, some of which are exposed in the limestone quarries, may extend to depths of several miles,” Burton said.

These faults, Burton said, are associated with rubbly zones that may be good conduits for groundwater, and the faults’ length and depth suggest that they may be good targets for exploration—particularly in the untapped volcanic core of the island.

In addition, Burton said, the faults may be associated with elevated temperatures at depth, and will be one of the subjects of the geothermal drilling project currently being conducted by Southern Methodist University.

“While Saipan is not very seismically active, whether or not one or more of these faults could play a role in a future earthquake remains an open question,” Burton said.

He said the previous geologic map, while very detailed, had been published in 1956 or before the advent of the plate-tectonic theory of geology and modern ideas about the formation of island arcs.

In this new geologic map project, Burton, who has a long experience in igneous and metamorphic rocks, studied the underlying volcanic rocks.

Weary, an expert in carbonate (limestone) mapping, studied the limestone formations.

Burton said they conducted the work both along roads and overland, commonly by hiking along streambeds.

When asked about the biggest problem they encountered, the geologist cited the thick vegetation, which obscured the bedrock and made for difficult traverses.

“The previous geologic mapping had been conducted soon after the war, when much of the landscape was more open and accessible,” Burton said.

The project to make a new geologic map of the island was conceived in 2004 after consulting with officials in the CNMI Legislature, the CNMI Water Task Force, the Commonwealth Utilities Corp., and USGS hydrologist Rob Carruth.

Carruth, who was then stationed on Saipan, recently published a report on Saipan’s groundwater resources.

Burton said that Carruth’s report states that the island’s tapped aquifers, which are exclusively limestone, are limited in extent and subject to salt-water contamination. At that time, Burton said, Saipan suffered chronic drinking water shortages, with few areas having a 24-hour water supply.

“We thought that a better understanding of Saipan’s geologic framework might lead to new sources of drinking water, including in the untapped volcanic core of the island,” Burton said.