Geologic time-series over millennia to minutes reveal life cycles of volcanoes and volcanic eruptions

Abstract:

Most real-time and near-real-time volcano monitoring data, including seismic, geodetic, infrasound, remote sensing, and gas, are commonly plotted and analyzed as time series. This allows an understanding of how active volcanic systems evolve with time, how precursory signals escalate (or deescalate), and how eruptions progress and ultimately end. Geologic data, such as composition, componentry, and volume of erupted material, are often not available at the same sampling rate and often have greater latency. Acquiring high-quality time series data of a geologic nature remains critical, however, in understanding magmatic systems over timescales of volcano growth as well as before and during eruptions.

At Augustine Volcano, Alaska, we have examined time series of petrologic data that provide evidence for changes in the magmatic plumbing system over millennia (Holocene) and also over single, well-sampled historical eruptions (e.g., 2006). Fe-Ti oxide, whole-rock, and glass compositions of early Holocene-through-recent tephra suggest that eruption temperatures increase with time, perhaps due to shallow storage regions requiring hotter temperatures to rejuvenate. In contrast to early Holocene eruptions that produced homogeneous and relatively voluminous magmas, recent eruptions, including the three most recent in 1976, 1986, and 2006, all produced modest volumes of low- through high-silica andesite. Strong compositional similarities between the products of recent eruptions suggest that the Augustine magmatic system had generally consistent crystallization conditions in the shallow crust over the past several decades. Despite this consistency, recent characterization of temporally constrained andesite pyroclasts from 2006 show subtle but significant diversity in temperature, fO2, and glass compositions that are difficult to explain by a single liquid line of descent and instead suggest tapping of multiple magma bodies with heterogenous composition and physical conditions even during single vulcanian explosions. These and other recent data suggest that current magmatic storage at Augustine consists of a spatially complex and heterogeneous system of small-volume intermediate magma bodies in the shallow crust and that geologically frequent injections of mafic magma drive eruptions.