Building volcanic ash records to date and correlate paleoenvironmental archives and improve volcanic histories

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Volcanic ashes (or tephra) are important for research reconstructing past environments and volcanic histories. Each tephra can be geochemically “fingerprinted” and dated, linking together the geologic records they were deposited in through space and time. Northwestern North America includes the Aleutian arc, the third most active volcanic arc in the world, and the less active, but more hazardous, Cascade arc. Surprisingly, tephra records for this region are underdeveloped, particularly for the most recent ~18,000 years. We are often missing critical data such as geochemistry, stratigraphy, age, and volcanic source. The overarching goal for my research program is to build a comprehensive volcanic record for NW North America that will inform both paleoenvironmental and volcanological studies. My proposal explores this long-term objective through these two themes:Building tephra frameworks to date, correlate and interpret records of past climate: Understanding how and why Earth's climate is changing today requires us to understand the natural variability of climate in the past. This is particularly relevant to Canada as northern regions experience amplified climate change. Key data for reconstructing past climate can be found in annually laminated (varved) lake deposits from SW Alaska, Canadian arctic ice cores held in the Canadian Ice Core Archive, and Gulf of Alaska marine sediment cores. Tephra are essential for dating and correlating these deposits to help interpret their significance, but few have been studied. This proposal presents several projects that will study tephra within these deposits, integrating them with one another, while building towards the objective of developing a tephra framework for future paleoenvironmental studies.Improving our understanding of volcanic processes and histories through tephra:Tephra are a fundamental component in parsing past volcanic events, such as the magnitude and frequency of past eruptions, the underlying processes driving them, and their hazards to modern society. Data used to examine these questions are often gathered from deposits close to or on the volcanoes, but reoccurring eruptions and erosion often destroys this proximal evidence of past eruptions. Distal (>10 km from source) tephra help fill these gaps and develop more complete volcanic histories. This aspect of the proposal is fundamentally intertwined with the previous theme, but here I focus on how tephra in these deposits can help us understand eruption histories and dynamics. For this specific proposal I aim to address some fundamental problems that hinder our ability to use tephra in this manner. This includes refining geochemical techniques for tracing tephra to their volcanic source or region, and examining historical eruptions, such as the 1980 eruption of Mount St. Helens, to improve our interpretation of pre-historic eruptions through their geologic records.