DENDROCHEMICAL ANALYSIS OF TREES AFFECTED BY THE PARÍCUTIN ERUPTION, WITH IMPLICATIONS FOR RE-ANALYZING THE SUNSET CRATER ERUPTION

To improve understanding of the full range of interactions between human groups and volcanic eruptions, we have begun a re-analysis of the dating of the last eruption of Sunset Crater, northern Arizona, long thought to have erupted in AD 1064. While the original dating was based on dendrochronological analysis of ring widths, our re-analysis uses dendrochemical techniques, namely the measurement and analysis of various chemical elements in dated tree rings.

To discover and calibrate potential dendrochemical signals from cinder cone eruptions generally, we started our re-analysis by investigating rings of trees growing around Volcano Parícutin, Michoacán, México, which last erupted from 1943 to 1952 in an event that is considered to have been geologically similar to the Sunset Crater eruption. Of particular note in Parícutin tree-ring samples that extend back in time to prior to the eruption, ring levels of phosphorus increased abruptly beginning in 1943 and dropped back again after 1952, although not to pre-eruption levels.

In archeological tree-ring samples from nearby Sunset Crater, ring levels of phosphorus also changed during the 11th century, though not exactly at AD 1064. If changes in ring phosphorus can truly be interpreted as evidence of cinder cone activity, then perhaps Sunset Crater had a more complex eruption sequence than is indicated by just the single-year date of 1064. Much work remains to verify these preliminary findings, but dendrochemistry might be a powerful tool to help refine dating certain past volcanic eruptions, thereby improving the archeological interpretations of human responses to them.