Abstract
Glacier Peak, a remote dacitic-andesitic stratovolcano in the North Cascade Range of Washington State, has an explosive eruptive history that has substantially impacted regional climate and ecosystems. Although the last confirmed eruption occurred between 3550 BCE and 200 CE, tephrochronology and records of Indigenous knowledge suggest a recent event around 1700 CE ± 100 years. Sparse historical records and limited chronological precision make dating this event challenging. In this study, we use long-lived Tsuga mertensiana [(Bong.) Carr.] trees to reconstruct 547 years of summer temperatures using latewood blue intensity (LWBI) as a temperature proxy. Our results reveal a significant positive relationship (r2 = 0.64, p < 0.0001) between LWBI values and March–September mean temperatures. A superposed epoch analysis confirms that the chronology captures cooling responses to well-established global volcanic eruptions, with tropical eruptions showing a one-year lag and extratropical eruptions occurring in the event year. Of the four years at or below the 1st percentile, a 1696 cooling anomaly (C) was the third coldest year of the past five centuries. This anomaly occurs within a broader interval of late-17th century Northern Hemisphere cooling linked to clustered volcanic forcing, including the 1693 Hekla eruption and a proposed mid-1690s tropical eruption, and therefore cannot be unequivocally attributed to a single source. However, statistical analysis of LWBI values, combined with Indigenous accounts, tephra evidence, and the spatially confined nature of the anomaly relative to surrounding Cascades chronologies, suggests an additional localized cooling influence potentially consistent with the most recent eruption of Glacier Peak. These results improve understanding of volcanic impacts on Pacific Northwest climate and provide new insight into pre-anthropogenic temperature variability. More broadly, this study demonstrates the value of tree-ring proxies, when integrated with geological and traditional knowledge records, for extending and refining historical reconstructions of volcanic activity.