Aug. 14, 2000 Until now, textbook depictions of the fiery magma chambers that reside beneath volcanoes and below the earth's crust were based on projected measurements, some guess work, and the artist's creative imagination. Scientists at Scripps Institution of Oceanography at the University of California, San Diego, have for the first time produced a direct three-dimensional image of a volcanic system based on sound waves reflected from a subterranean magma chamber. An international research team used a two-mile long array of hydrophones, instruments used for listening to sound transmitted through water, to record sound signals reflected from a magma chamber residing one mile beneath the East Pacific Rise, a linear volcanic system some 600 miles southwest of Acapulco, Mexico.
"We were able to take bits and pieces of reflected sound energy and project them back onto the magma body, producing a direct 3-D image, which is much more detailed than those delivered using non-direct methods," said Graham Kent, an associate research geophysicist at the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps. "Our image is constructed from energy reflecting off of a thin tabular sheet of lava beneath the ridge crest in a manner analogous to a sonogram."
Results of the ARAD project (Anatomy of a Ridge-Axis Discontinuity) are described in the August 10 issue of the journal Nature.
The team's images reveal a large and complex magma chamber system beneath a section of the East Pacific Rise where the ridge is misaligned. These results contradict the current paradigm, which describes these complex features with little or no magma supply.
The authors argue that clear, three-dimensional depictions such as those constructed for the East Pacific Rise images will provide new insights into the geological processes of other volcanic systems worldwide. Such images are important for understanding the hidden processes inside a volcanic system's magma chamber, which may give further insight into volcanic activity and the composition of erupted lava flows.
These three-dimensional images of the mid-ocean ridge magma chamber benefited from Global Positioning System (GPS) navigation, which the researchers used to carefully plot their course across the East Pacific Rise. The three-dimensional images were constructed from some 120,000 sound records. The hydrophone instruments record "popping sounds" released from a series of air guns aimed at the crustal magma chambers.
### The paper's co-authors from Scripps include Alistair Harding and John Orcutt. Other co-authors include S.C. Singh, M.C. Sinha, P.J. Barton, R.S. White, S.K. Bazin, R.W. Hobbs, C.H. Tong, and J.W. Pye.
The ARAD seismic experiment is an international collaboration between investigators at Scripps and the University of Cambridge, United Kingdom, with financial support from the RIDGE program/National Science Foundation, British Institutions Reflection Profiling Syndicate (BIRPS), and the Natural Environment Research Council. Additional funds were provided by Scripps Institution and the Cecil H. and Ida M. Green Foundation for Earth Sciences.
Note to editors: 3-D movie available at: http://www.sio.ucsd.edu/scripps_news/pressreleases/3d-volcano_movies.html
Scripps Institution of Oceanography, a part of the University of California, San Diego, is one of the oldest, largest, and most important centers for global science research and graduate training in the world. In 1995, the National Research Council ranked Scripps Institution first in faculty quality among oceanography programs nationwide. The scientific scope of the institution has grown since its founding in 1903 to include biological, physical, chemical, geological, geophysical, and atmospheric studies of the earth as a system. More than 300 research programs are under way today in a wide range of scientific areas. The institution has a staff of about 1,200, and annual expenditures of approximately $100 million, from federal, state, and private sources. Scripps operates the largest academic fleet with four oceanographic research ships for worldwide exploration and one research platform.
Scripps Institution of Oceanography on the web: http://www.sio.ucsd.edu/
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