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Tuesday, Dec. 17, 1996

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First detailed images of New Mexico volcano show that Valles caldera . . .
When the walls come tumbling down: Controlled mine collapse helps . . .
UC "hot site"
Environmental surveillance reports online
Stockpile stewardship to be featured on CNN
Lab's science education programs consolidate

First detailed images of New Mexico volcano show that Valles Caldera still underlain by magmatic melt

A three-year study of seismic waves traveling through the heart of an ancient volcano has provided researchers at the Laboratory the first comprehensive three-dimensional model of the caldera revealing new and important information about its plumbing system.

Lab scientist Lee Steck of GeoEngineering (EES-4) and University of Wisconsin researcher William Lutter led a team of researchers who recorded travel times of teleseismic waves from distant earthquakes traveling through the Valles Caldera in Northern New Mexico. The seismic waves used in the analysis are essentially sound waves that travel faster in stiffer material and slow down in less stiff material, such as magma.

Researchers found the seismic waves slowed down by as much as 35 percent beneath the caldera as compared to normal crust outside the caldera. Using tomography, a method similar to the computer aided tomography or CAT scans in medical imaging, geophysicists produced a 3-D computer model that seismic waves travel slower beneath the Valles Caldera.

In a poster session Monday at the American Geophysical Union conference, Steck and Lutter presented their findings.

The Valles Caldera is about 70 miles north of Albuquerque. It formed during two explosive episodes occurring 1.6 million years ago and 1.2 million years ago when more than 90 cubic miles of rock erupted. The most recent volcanic activity ended 50,000 years ago.

The 14-mile-wide Valles Caldera is one of the most well-known resurgent calderas in the United States. Scientists have been studying this region since the 1920s to learn about the fundamental processes of magmatism, hydrothermal systems and ore deposition.

Resurgent calderas form following a huge eruption when the roof of the magma chamber collapses into the space voided by the erupted, gas-rich magma. The collapsed crater then fills with its own volcanic ash and pumice.

In the Valles Caldera, the research team placed 50 seismic monitoring stations around and within the caldera that produced a detailed picture of the velocity structure down to depths of 24 miles below the surface. Data were gathered from 216 distant earthquakes most of which occurred during the 1993 and 1994 Jemez Tomography Experiment. Data gathered from a 1987 experiment by Laboratory researcher Peter Roberts was also included in the study.

Researchers analyzed 4,872 seismic waves that travel fairly quickly through Earth's crust. Seismic waves from far away earthquakes approach the instruments nearly vertically, while seismic waves from earthquakes that are closer come in at a more horizontal angle. The researchers need both near and far earthquakes for a wide variety of angles to produce the 3-D model.

When the Valles Caldera collapsed nearly 1.2 million years ago, researchers believe it occurred in a more stair-stepped than piston-like manner resulting in deeper areas filled with more volcanic ash and sediments. Steck and Lutter's research confirms that theory.

The research team found several areas of shallow low velocity zones slightly deeper than a mile from the caldera floor that were slower than surrounding areas by about minus 10 to 17 percent. The research team believes these represent the ponding of pyroclastic deposits that resulted from a deeper collapse on one side of the caldera .

A significant finding is an area of low velocity beginning at four miles deep with an eight mile diameter that is 35 percent slower than surrounding areas. Steck and Lutter say this can be accounted for by molten material that may be between 10 to 25 percent of the total volume.

There are three possible interpretations of the 3-D image data. The first is that the original million-year-old magma is still cooling underneath the caldera. The second is that the original magma may be rejuvenated or in communication with the mantle to periodically receive more melt. The third interpretation is that new magma is different from the original.

Steck and Lutter agree that the original magma may still exist and could retain up to 10 percent of its melt products. However, they say, these calculations require numerous simplifying assumptions and may not be realistic.

A third, unexpected finding was a low-velocity zone at about 23 miles below the surface, near the boundary between Earth's crust and mantle, which may also be melt or crystallized melt.

The research method can only image an area larger than about one mile. If there are conduits or connections between the magma chamber and the deeper low velocity region and they are smaller than a mile wide or long, the technology cannot image them.

The research project is part of the Jemez Tomography Experiment, a cooperative and interdisciplinary research program involving scientists from Los Alamos, University of Wisconsin, San Diego State University, University of Texas at Dallas and El Paso, Purdue University, the University of Utah Research Institute and the U.S. Geological Survey.

--Kathy DeLucas

When the walls come tumbling down: Controlled mine collapse helps test-ban verification efforts

When mine operators purposely collapsed a section of a Michigan copper mine last September, Laboratory researchers were quietly collecting seismic signals, trying to see how the event might compare to, say, a nuclear blast ...

The collapse, induced with the help of explosives, was an innovative way of doing business for the mine's operators; but for researchers it was an opportunity to gather information that ultimately could help world leaders determine if a rogue nation violates the Comprehensive Test Ban Treaty.

Scott Phillips and Craig Pearson of Geophysics (EES-3) Monday at the American Geophysical Union's Fall Meeting presented data obtained during the induced collapse of a portion of the White Pine Mine located in Michigan's Upper Peninsula.

Phillips, Pearson and colleagues used seismometers to gather data before, during and after the controlled collapse last September and during a similar collapse in September 1995.

"The seismic data we collected is useful because it will help scientists distinguish between events like earthquakes or mine collapses and nuclear explosions," Phillips said.

Los Alamos researchers are developing a complete seismic library that will help scientists pinpoint the origin of an explosion and whether such an explosion has a "nuclear fingerprint" - a distinct pattern of shock waves.

"The White Pine Mine collapse data will be like one page in a book in the library," Phillips said. "But it will be a page that contains some very interesting data."

As part of the CTBT, an international organization will set up a series of seismic monitoring stations around the globe. Data from each station will be transmitted to an international data center. From there, scientists can analyze whether specific seismic events were nuclear tests or something else.

"In this case, we found out a couple of things relevant to the Comprehensive Test Ban Treaty," Phillips said. "First, we found that we can detect useful signals from an event of this size - around magnitude three on the Richter Scale - from as far as about 600 miles away. This will help treaty verifiers assess the capability and usefulness of a network of monitoring stations.

"Next, we found that from our close-in monitoring stations, the signals from the explosives were very distinct from the signals generated by the collapse of the mine cavity - and we weren't sure whether this would be the case going in. Finally, we found that most of the aftershocks, caused when rock settles after the initial collapse, happened in the first four hours after the collapse, meaning that it might be extremely difficult to set up stations close to a seismic signal origin to help pinpoint the exact location of an event that initially was detected by far-away stations."

But why would anyone want to collapse a mine in the first place?

The induced collapses were part of an experimental mining operation at White Pine, a nearly 20-square mile underground copper mine located about five miles south of the southern shore of Lake Superior. The mine is reaching the end of its economic life and the induced collapses allowed mine operators to extract copper that otherwise would have been left behind in support pillars.

At White Pine, raw copper ore is trapped inside dense rock found 300 to 500 meters below the surface. During mining operations, ore was removed and the copper was refined at the surface.

To ensure that the mine remained stable during normal operations, huge pillars of rock were left in place to shore up subterranean areas. The nine-foot-tall pillars, each measuring 30 feet by 60 feet, pepper the underground caverns. Consequently, about 50 percent of the ore could not be mined because it remained in the pillars.

Mine operators came up with a novel way of extracting the remaining copper: They used explosives to turn the pillars into rubble and subsequently delivered a leaching solution into the area. The solution then was pumped to the surface and copper was extracted by an electrolytic process. The operators conducted the experimental mining procedure to assess whether the method was economically feasible.

"The seismic data we obtained also yielded information that was crucial to the mining industry," said Phillips.

Thanks to close-in seismometer placement, he and colleagues were able to pinpoint 135 distinct, aftershocks that occurred within 36 hours of the collapse. After that, most of the subterranean settling ceased.

After painstakingly analyzing the data, Phillips determined that the aftershocks were situated in a tight pattern about 100 meters thick above the collapsed area. The pattern was similar in size to a pattern predicted by mine engineers, who based their pattern on theoretical models and on rock properties.

"They predicted the size of the aftershock pattern," Phillips said, "but they were slightly off on its position - they had their pattern directly above the collapsed area; our data showed that it was shifted toward the west. We hope the aftershock patterns will help us understand the changes in stress within the rock following the collapse."

Phillips said the seismic data was shared with mine officials and may help them to better engineer underground mines and mining operations in the future.

"The cooperation we received was invaluable," he said. "From outside the mine, it's rare that you can know exactly when and where an unplanned underground collapse is going to occur. This gave us a unique opportunity to check the character of seismic signals and to analyze the entire event as it unfolded."

Phillips' and Pearson's Los Alamos collaborators on the work were Brian Stump, C.L. Edwards, Diane Baker and Roy Boyd of EES-3.

--James E. Rickman

UC "hot site"

This week's "hot World Wide Web page" for the University of California system is the page maintained by the UC's Northern New Mexico Office in downtown Los Alamos. Hot pages are selected each week by UC to point out examples of innovative, well designed and informative pages. The purpose is to give others throughout the UC system some good ideas about how to present their information. Previous hot pages from the Laboratory have included the ALEXIS project, views of the solar system and Field Unit 4 of the Environmental Restoration Project. go to

Environmental surveillance reports online

Three reports dealing with environmental issues in and around the Laboratory are now online. One report and a shorter, summary report address monitorings of the Lab's air and water quality, soils and foodstuffs and compliance with federal regulations. The third report deals with a 28-acre piece of property off DP Road that the Department of Energy has proposed giving to Los Alamos County.

The entire report, "Environmental Surveillance at Los Alamos during 1995" can be found at http://lib-www.lanl.gov/pubs/la-13210.htm online on the World Wide Web.

"Summary of Environmental Surveillance at Los Alamos during 1995" can be found online at http://lib-www.lanl.gov/la-pubs/00326114.pdf on the World Wide Web. The report is produced by the Environmental Reports team in the Ecology (ESH-20) Group and available on the World Wide Web with the assistance of the Research Library (CIC-14).

This report describes the Lab's environmental surveillance activities to determine compliance with state and federal standards and to convey environmental data, according to Julie Johnston of ESH-20.

Groundwater, ambient air, surface water, the county's water supply, soils, sediments and foodstuffs all are monitored for external penetrating radiation, quantities of airborne emissions and liquid effluents and concentrations of chemicals and radionuclides, said Johnston.

The report concluded that the environmental effects from Lab operations are small and don't pose a demonstratable threat to the public, Lab employees or the environnment.

The 28-acre piece of property DOE wants to turn over to Los Alamos County is off DP Road. According to the draft land transfer environmental assessment, the action is proposed to accelerate economic development opportunities in the county because the land could be used to attract businesses which in turn would create additional job opportunities.

The draft report said developing the DP Road property would create an estimated 450 new jobs and 585 indirect jobs, while reducing the size of the Lab by only one-tenth of one percent

The report also said the proposed transfer of the 28 acres to the county wouldn't create any adverse health effects.

This report can be found at http://lib-www.lanl.gov/pubs/Environment.htm online.

--Steve Sandoval

Stockpile stewardship to be featured on CNN

The Laboratory's work in stockpile stewardship is the subject of a report to be shown on Cable News Network's "Science and Technology" show at 9 a.m. Saturday. Part two of the report is scheduled to be broadcast next Saturday, Dec. 28. Lab personnel and research also will be featured on "CNN Presents" at 7 p.m., this Sunday, Dec. 22. Alan Perelson of Theoretical Biology and Biophysics (T-10) will talk about his research on Acquired Immune Deficiency Syndrome (AIDS).

Lab's science education programs consolidate

The Science Education and Outreach Group of the Human Resources (HR) Division is moving.

Beginning Jan. 6, SEO will become a part of the Science and Technology Base (STB) Programs Office.

"This move will consolidate much of the Laboratory's science education program effort within STB," said STB Director Al Sattelberger.

He noted that the Science Education Program Office and the University Programs Team already are under the auspices of STB.

SEO will continue to sponsor student-oriented science programs, said Sattelberger, also noting that no current SEO employee will lose his or her job as a result of the move.

The move also helps the Lab more closely coordinate education programs, Sattelberger added.

The 10-employee Science Education and Outreach Group is now located at Technical Area 3. It will stay there until about February when its offices are relocating to the Canyon School Complex.

Dolores Jacobs will be the acting team leader during the transition to STB.

Judith Kaye, the current group leader for SEO, will become the new group leader for HR's Training and Development Group.

--Steve Sandoval

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