Abstract
Glacier Peak, a remote dacitic-andesitic stratovolcano in the North Cascade Range of WashingtonState, has an explosive eruptive history that has substantially impacted regional climates and
ecosystems. While the last confirmed eruption occurred between 3550 BCE and 200 CE,
tephrochronology and Indigenous knowledge suggest a more recent event around 1700 CE ± 100
years. The challenge of dating this eruption is compounded by the lack of carbon-rich tephra for
radiometric dating and sparse historical records. In this study, we use long-lived Tsuga mertensiana
trees to reconstruct summer temperatures over the past 548 years, using latewood blue intensity
(LWBI) as a temperature proxy. Our results reveal a significant and positive correlation (r² = 0.64, p
< 0.0001) between LWBI values and March-September mean temperatures. The reconstruction
identified periods of pronounced warm anomalies, such as the 1796-1800 event, and cooling
anomalies, notably in 1954, 1601, and 1696. A superposed epoch analysis (SEA) confirmed that the
Glacier Peak chronology captures lagged cooling signals from global volcanic eruptions, with tropical
eruptions showing a one-year lag and extratropical eruptions having an immediate impact. The 1696
cooling anomaly, not associated with known global eruptions, was identified as the third coldest year
in the record. Statistical analysis of LWBI values, combined with Indigenous accounts and tephra
evidence, suggests this anomaly is linked to a previously undocumented eruption of Glacier Peak.
Our findings enhance the understanding of volcanic impacts on Pacific Northwest climates and
provide insights into pre-anthropogenic temperature variability in the region. These findings,
supported by traditional knowledge and tephrochronology, highlight the utility of tree-ring analysis in
extending the historical record of volcanic activity. Future research using quantitative wood anatomy
may further refine the seasonal timing of the proposed 1696 eruption.