A DENDROCHEMICAL STUDY OF THE 1980 ERUPTION OF MOUNT ST. HELENS

Inductively coupled plasma optical emission spectroscopy (ICP-OES) and isotope ratio mass spectrometry (IRMS) were used to investigate changes in the elemental and isotopic composition in tree-ring sequences from Mount St. Helens, Washington. The goal of this study was to target a known eruption event and identify potential chemical and isotopic markers recorded in tree rings. Individual growth rings from between 1967-1975 and 1990-1995 were sampled from four spruce (Picea sp.) trees. The sampled trees were confined to an area bound by the Cowlitz River, located N of the vent, and Clear Creek, located ESE of the vent. Statistical findings from this study suggest that the elemental compositions of several major elements (i.e. B, Ba, Ca, K, Mg, Na, and P) in the growth rings differ before and after the eruption event. However, these trends may be indicative of more complex and localized interactions between the trees and their environment. Here, we present a thorough statistical treatment of the elemental and isotopic composition data as a means of identifying potential links between chemical signatures in tree-rings and specific eruption events.