 Emphasis Area:
Volcano/Atmosphere Interactions
Principal Investigator(s): J. Diehl, W. Rose
Sponsor: National Science Foundation
Funding Level: $185,000
Period: 2005 to 2008
Abstract:
Growing evidence suggests that normal and reversed polarity chrons are riddled by numerous short-lived
periods of geomagnetic instability, some of which affect the geomagnetic field globally whereas others are
more local in extent. In either case, these periods of instability or excursions of the geomagnetic field are
generally expressed in the rock record by paleomagnetic directions whose variation is outside the normal
bounds of secular variation to the point of being almost fully reversed and/or by paleointensity values which
are considered abnormally low. Excursions that can be documented paleomagnetically as being global and
dated precisely and accurately are important stratigraphic markers and are critical to our understanding
geodynamo processes. The problem therefore is distinguishing between excursions that are global from those
which are merely large amplitude secular variation features of regional extent. For the Brunhes Chron,
evidence for many of excursions comes from the sedimentary record where dating is problematic and
directional data not as reliable as from volcanic rocks. The Mono Lake is a classic example; paleomagnetic
records of this event (~34 ka) are almost exclusively from sediments and appear to be restricted in areal extent.
Thus, there remains considerable debate as to whether it is a global event. Several recent studies of lava flows
present evidence for the Mono Lake event, but either lack precise radioisotopic ages, or are based on
incomplete paleomagnetic data.
Intellectual Merit
Paleomagnetic directions determined from oriented block samples (collected by Rose et al., 1977) and from
eight paleomagnetic sites drilled in lava flows from Santa Maria volcano, Guatemala in 1990 define a pattern
of variation similar to the pattern of geomagnetic field changes recorded by the sediments of the Wilson Creek
Formation near Mono Lake, California. This led Conway et al. (1994) to suggest that these flows had recorded
the Mono Lake reversal excursion. The correlation was made on pattern recognition alone and relied more on
a well-defined inclination dataset than on the declination data; no radioisotopic ages were available.
To test the hypothesis that this lava flow sequence records the Mono Lake excursion and that this event is
global in extent, we propose to return to the volcano and re-drill and date the entire sequence (~25 lava
flows) exposed in the crater wall of Santa Maria. The objectives and merit of this study include:
A full characterization of the geomagnetic field variations recorded by these lava flows
A precisely determined age of the geomagnetic event using the 40Ar/39Ar incremental heating method
Unequivocal evidence for a global Mono Lake event from lavas if 40Ar/39Ar ages bear out our hypothesis
If the 40Ar/39Ar age (preliminary experiments suggest that the lava flows erupted between about 55 and 22
ka) does not match that of the Mono Lake, then the alternative possibility that the older Laschamp or
younger Hilina Pali event may be recorded is equally important
Well-defined 40Ar/39Ar ages for the lava flows at Santa Maria will place important boundary
conditions on the volcanic flux for the latter stages of growth of Santa Maria’s cone.
Broader Impacts
We have worked closely with Guatemalan volcanologists at monitoring and hazards agencies (INSIVUMEH
and CONRED) for more than 35 years, developing a synergistic relationship where we provide access to
advanced laboratory and research applications and they supply strong field context for obtaining relevant
samples. In recent years, several Central American volcanologists obtained degrees at Michigan Tech. This
research will continue that tradition. The proposed work will be carried out by Rüdiger Escobar as part of his
MS degree at Michigan Tech. Rüdiger is an experienced volcanologist at CONRED with a Civil Engineering
BS and many skills learned during several years of volcanological work in Guatemala (GIS, GPS, geological
mapping). He is also a veteran climber who knows the Guatemalan volcanoes like few other people. His
expertise and experience are expected to be valuable for the work in the crater of Santa María. After
completing his MS degree, Rüdiger will return to Guatemala where he is expected to provide leadership in
important volcanic hazards work for decades.
Last Update: October 11, 2007
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