Kristi L. Wallace

The reawakening of Alaska's Augustine volcano

Augustine volcano, in south central Alaska, ended a 20-year period of repose on 11 January 2006 with 13 explosive eruptions in 20 days. Explosive activity shifted to a quieter effusion of lava in early February, forming a new summit lava dome and two short, blocky lava flows by late March (Figure 1). The eruption was heralded by eight months of increasing seismicity, deformation, gas emission, and small phreatic eruptions, the latter consisting of explosions of steam and debris caused by heating and expansion of groundwater due to an underlying heat source.

Alaska Volcano Observatory Alert and Forecasting Timeliness: 1989–2017

The Alaska Volcano Observatory (AVO) monitors volcanoes in Alaska and issues notifications and warnings of volcanic unrest and eruption. We evaluate the timeliness and accuracy of eruption forecasts for 53 eruptions at 20 volcanoes, beginning with Mount Redoubt’s 1989–1990 eruption. Successful forecasts are defined as those where AVO issued a formal warning before eruption onset. These warning notifications are now part of AVO’s Aviation Color Code and Volcanic Alert Level. This analysis considers only the start of an eruption, although many eruptions have multiple phases of activity. For the 21 eruptions at volcanoes with functioning local seismic networks, AVO has high forecasting success at volcanoes with: >15 yr repose intervals and magmatic eruptions (4 out of 4, 100%); or larger eruptions (Volcanic Explosivity Index (VEI) 3 or greater; 6 out of 10, 60%). AVO successfully forecast all four monitored, longer-repose period, VEI 3+ eruptions: Redoubt 1989-1990 and 2009, Spurr 1992, and Augustine 2005–2006. For volcanoes with functioning seismic monitoring networks, success rates are lower for: volcanoes with shorter repose periods (3 out of 16, 19%); more mafic compositions (3 out of 18, 17%); or smaller eruption size (VEI 2 or less, 1 out of 11, 9%). These eruptions (Okmok, Pavlof, Veniaminof, and Shishaldin) often lack detectable precursory signals. For 32 eruptions at volcanoes without functioning local seismic networks, the forecasting success rate is much lower (2, 6%; Kasatochi 2008 and Shishaldin 2014). For remote volcanoes where the main hazard is to aviation, rapid detection is a goal in the absence of in situ monitoring. Eruption detection has improved in recent years, shown by a decrease in the time between eruption onset and notification. Even limited seismic monitoring can detect precursory activity at volcanoes with certain characteristics (intermediate composition, longer repose times, larger eruptions), but difficulty persists in detecting subtle precursory activity at frequently active volcanoes with more mafic compositions. This suggests that volcano-specific characteristics should be considered when designing monitoring programs and evaluating forecasting success. More proximally-located sensors and data types are likely needed to forecast eruptive activity at frequently-active, more mafic volcanoes that generally produce smaller eruptions.

Radiocarbon Age of Soil Organic Matter Fractions Buried by Tephra in Alaska

Radiocarbon ages were determined on different fractions extracted from buried paleosols in south-central Alaska as an experiment to establish best practices for analysis of low-organic-matter paleosols. Seven samples were collected from directly beneath tephra deposits to determine the eruption frequency of Mount Spurr Volcano, Alaska. Soil development near the volcano is poor due to the high-latitude climate and frequent burial of soil surfaces by tephra. Contamination of soils by local wind-blown material is a concern. The humic acid 14 C ages are consistently younger than both the bulk soil and residue after extraction ages. The difference in ages between the humic acid extract and bulk soil range from 60–1130 14 C yr BP and 180–4110 14 C yr BP, respectively, for residue. Previous observations from dating different soil fractions show that residue ages are typically younger than humic acid extracts presumably because they contain a fraction of younger plant material including roots. We attribute the older ages to contamination by old carbon from eolian charcoal particles. This study supports the use of accelerator mass spectrometry (AMS) 14 C dating of the humic acid fraction in order to estimate the age of soil that presumably marks the age of burial and avoids suspected contamination by old carbon.

Short-Term Forecasting and Detection of Explosions During the 2016–2017 Eruption of Bogoslof Volcano, Alaska

We describe a multidisciplinary approach to forecast, rapidly detect, and characterize explosive events during the 2016–2017 eruption of Bogoslof volcano, a back-arc shallow submarine volcano in Alaska’s Aleutian arc. The eruptive sequence began in December 2016 and included over 60 discrete explosive events. Because the volcano has no local monitoring stations, we used distant stations on the nearest volcanoes, Okmok (54 km) and Makushin (72 km), combined with regional infrasound sensors and lightning detection from the Worldwide Lightning Location Network (WWLLN). Monitoring of activity used a combination of scheduled checks combined with automated alarms. Alarms triggered on real-time data included real-time seismic amplitude measurement (RSAM); infrasound from several arrays, the closest being on Okmok; and lightning strokes detected from WWLLN within a 20-km radius of the volcano. During periods of unrest, a multidisciplinary response team of four people fulfilled specific roles to evaluate geophysical and remote-sensing data, event-specific ash-cloud dispersion modeling, interagency coordination, and development and distribution of formalized warning products. Using this approach, for events that produced ash clouds ≥7.5 km above sea level, AVO called emergency response partners 15 minutes, and issued written notices 30 minutes, after event onset (mean times). Factors that affect timeliness of written warnings include event size and number of data streams available; bigger events and more data both decrease uncertainty and allow for faster warnings. In remote areas where airborne ash is the primary hazard, the approach used at Bogoslof is an effective strategy for hazard mitigation.

Communication Demands of Volcanic Ashfall Events

Volcanic ash is generated in explosive volcanic eruptions, dispersed by prevailing winds and may be deposited onto communities hundreds or even thousands of kilometres away. The wide geographic reach of ashfalls makes them the volcanic hazard most likely to affect the greatest numbers of people. However, forecasting how much ash will fall, where, and with what characteristics, is a major challenge. Varying social contexts, ashfall characteristics, and eruption durations create unique challenges in determining impacts, which are wide-ranging and often poorly understood. Consequently, a suite of communication strategies must be applied across a variety of different settings. Broadly speaking, the level of impact depends upon the amount of ash deposited and its characteristics (hazard), as well as the numbers and distribution of people and assets (exposure), and the ability of people and assets to cope with the ashfall (resilience and/or vulnerability). Greater knowledge of the likely impact can support mitigation actions, crisis planning, and emergency management activities. Careful, considered, and well-planned communication prior to, and during, a volcanic ashfall crisis can substantially reduce physical, economic and psychosocial impacts. We describe the factors contributing to the complex communication environment associated with ashfall hazards, describe currently available information products and tools, and reflect on lessons from a range of case-study ashfall events. We discuss currently-available communication tools for the key sectors of public health, agriculture and critical infrastructure, and information demands created by ash clean-up operations. We conclude with reflections on the particular challenges posed by long-term eruptions and implications for recovery after ashfall.

Timing, distribution, and character of tephra fall from the 2005-2006 eruption of Augustine Volcano: Chaper 9 in The 2006 eruption of Augustine Volcano

The 2005–6 eruption of Augustine Volcano produced tephra-fall deposits during each of four eruptive phases. Late in the precursory phase (December 2005), small phreatic explosions produced small-volume, localized, mostly nonjuvenile tephra. The greatest volume of tephra was produced during the explosive phase (January 11–28, 2006) when 13 discrete Vulcanian explosions generated ash plumes between 4 and 14 km above mean sea level (asl). A succession of juvenile tephra with compositions from low-silica to high-silica andesite is consistent with the eruption of two distinct magmas, represented also by a low-silica andesite lava dome (January 13–16) followed by a high-silica andesite lave dome (January 17–27). On-island deposits of lapilli to coarse ash originated from discrete vent explosions, whereas fine-grained, massive deposits were elutriated from pyroclastic flows and rock falls. During the continuous phase (January 28–February 10, 2006), steady growth and subsequent collapses of a high-silica andesite lava dome caused continuous low-level ash emissions and resulting fine elutriate ash deposits. The emplacement of a summit lava dome and lava flows of low-silica andesite during the effusive phase (March 3–16, 2006) resulted in localized, fine-grained elutriated ash deposits from small block-and-ash flows off the steep-sided lava flows. Mixing of two end-member magmas (low-silica and highsilica andesite) is evidenced by the overall similarities between tephra-fall and contemporaneous lava-dome and flow lithologies and by the chemical heterogeneity of matrix glass compositions of coarse lapilli and glass shards in the ash-size fraction throughout the 2005–6 eruption. A total mass of 2.2×1010 kg of tephra fell (bulk volume of 2.2×107 m3 and DRE volume of 8.5×106 m3) during the explosive phase, as calculated by extrapolation of mass data from a single Vulcanian blast on January 17. Total tephra-fall volume for the 2005–6 eruption is about an order of magnitude smaller than other historical eruptions from Augustine Volcano. Ash plumes of short duration and small volume caused no more than minor amounts (≤1 mm) of ash to fall on villages and towns in the lower Cook Inlet region, and thus little hazard was posed to local communities. The bulk of the ash fell into Cook Inlet. Monitoring by the Alaska Volcano Observatory during the eruption helped to prevent hazardous encounters of ash and aircraft.