Okmok Volcano Research Articles

A New Multi‐Method Assessment of Stratospheric Sulfur Load From the Okmok II Caldera‐Forming Eruption of 43 BCE

AbstractThe 43 BCE eruption of Okmok Volcano has been proposed to have had a significant climate cooling impact in the Northern Hemisphere. In this study, we quantify the climate cooling potential of the Okmok II eruption by measuring sulfur concentration in melt inclusions (up to 1,606 ppm) and matrix glasses and estimate a total of 62 ± 16 Tg S released. The proportion reaching the stratosphere (2.5%–25%, i.e., 1.5–15.5 Tg S) was constrained by physical modeling of the caldera‐collapse eruption. Using the NASA Goddard Institute for Space Studies E2.2 climate model we found a linear response between cooling and stratospheric sulfur load (0.05–0.08°C/Tg S). Thus, the 1–2°C of cooling derived from proxy records would require 16–32 Tg sulfur injection. This study underscores the importance of combining approaches to estimate stratospheric S load. For Okmok II, we find all methods are consistent with a range of 15–16 Tg S.

Earthquakes Record Cycles of Opening and Closing in the Enhanced Seismic Catalog of the 2008 Okmok Volcano, Alaska, Eruption

AbstractSeismicity during explosive volcanic eruptions remains challenging to observe through the eruptive noise, leaving first‐order questions unanswered. How do earthquake rates change as eruptions progress, and what is their relationship to the opening and closing of the eruptive vent? To address these questions for the Okmok Volcano 2008 explosive eruption, Volcano Explosivity Index 4, we utilized modern detection methods to enhance the existing earthquake catalog. Our enhanced catalog detected significantly more earthquakes than traditional methods. We located, relocated, determined magnitudes and classified all events within this catalog. Our analysis reveals distinct behaviors for long‐period (LP) and volcano‐tectonic (VT) earthquakes, providing insights into the opening and closing cycle. LP earthquakes occur as bursts beneath the eruptive vent and do not coincide in time with the plumes, indicating their relationship to an eruptive process that occurs at a high pressurization state, that is, partially closed conduit. In contrast, VT earthquakes maintain a steadier rate over a broader region, do not track the caldera deflation and have a larger b‐value during the eruption than before or after. The closing sequence is marked by a burst of LPs followed by small VTs south of the volcano. The opening sequence differs as only VTs extend to depth and migrate within minutes of the eruption onset. Our high‐resolution catalog offers valuable insights, demonstrating that volcanic conduits can transition between partially closed (clogged) and open (cracked) states during an eruption. Utilizing modern earthquake processing techniques enables clearer understanding of eruptions and holds promise for studying other volcanic events.

A Specific Earthquake Processing Workflow for Studying Long‐Lived, Explosive Volcanic Eruptions With Application to the 2008 Okmok Volcano, Alaska, Eruption

AbstractBy providing unrivaled resolution in both time and space, volcano seismicity helps to chronicle and interpret eruptions. Standard earthquake detection methods are often insufficient as the eruption itself produces continuous seismic waves that obscure earthquake signals. We address this problem by developing an earthquake processing workflow specific to a high‐noise volcanic environment and applying it to the explosive 2008 Okmok Volcano eruption. This process includes applying single‐channel template matching combined with machine‐learning and fingerprint‐based techniques to expand the existing earthquake catalog of the eruption. We detected an order of magnitude more earthquakes, then located, relocated, determined locally calibrated magnitudes, and classified the events in the enhanced catalog. This new high‐resolution earthquake catalog increases the number of observations by about a factor of 10 and enables the detailed spatiotemporal seismic analysis during a large eruption.

Serpentinite fluids and slab-melting in the Aleutian arc: Evidence from molybdenum isotopes and boron systematics

Mo isotope compositions have been increasingly used as a source tracer in magmatic systems. Here, we investigate the relative role of subducting oceanic crust, fluid-rich sources (e.g., serpentinite, altered oceanic crust – AOC), subducted sediments and upper mantle in the chemical composition of Aleutian arc magmas with Mo and B systematics. We present elemental and Mo isotope compositions (δ98/95Mo) and B concentrations on Aleutian lavas (n = 59), from Okmok Volcano in the east to the westernmost seamount Piip, showing absence of Mo isotope fractionation during magmatic differentiation. Additionally, we report Mo isotope systematics for serpentinized peridotites from the South-West Indian Ridge (SWIR) (n = 6), AOC (n = 2) and Pacific sediments (DSDP 183, ODP 886) (n = 5) outboard the Aleutian arc. Molybdenum isotope composition and B enrichment (e.g., B/Ce) patterns display a step-function increase along the arc, with low, MORB-like, δ98/95Mo and low B/Ce values in the western section of the arc (B/Ce = 0.15–1.07; δ98/95Mo =−0.38 to +0.01‰), that abruptly increase in the central-eastern volcanoes Korovin, Seguam and Yunaska (B/Ce = 1.20–2.60; δ98/95Mo = +0.03 to +0.30‰) near the intersection of the Amlia Fracture Zone (AFZ) with the trench, but decrease again farther east at Okmok (B/Ce = 0.76 and δ98/95Mo = −0.12‰ on average). These data patterns are interpreted to reflect an along-arc changing source in the Aleutian magmas. AOC and Pacific sediments have predominantly low δ98/95Mo (−0.47 to −0.32 and +0.17 to −1.9‰, respectively), while serpentinites have extremely high δ98/95Mo (up to +1.09‰) and high B/Ce (∼22000). Based on the low δ98/95Mo in sediments and AOC, and lack of correlation between along-arc δ98/95Mo and radiogenic sediment tracers, subducted sediments and AOC do not exert first-order controls on the observed Mo isotope compositions. Rather, low, MORB-like, δ98/95Mo but high Mo enrichments (e.g., Mo/Ce) in the western samples are consistent with slab melting under rutile-bearing eclogitic facies with near absent Mo isotope fractionation from the slab to the arc sources. In turn, the abrupt increase of δ98/95Mo and B/Ce in lavas near the AFZ are best explained by a serpentinite endmember (likely dehydration fluids) at the AFZ that is not evident elsewhere along the arc. Results from this study provide evidence for serpentinites as an additional heavy Mo isotope signature component in subduction zones and demonstrate that high δ98/95Mo coupled with B enrichments are a useful proxy for tracing serpentinite fluids in subduction zones.

Inflation of Okmok Volcano During 2008–2020 From PS Analyses and Source Inversion With Finite Element Models

AbstractOkmok volcano, located on northeastern Umnak Island along the eastern end of the Aleutian island arc, is one of the most active volcanoes in Alaska, producing multiple eruptions in the past century. The most recent eruption, which occurred during July–August of 2008, was the most explosive since the early nineteenth century. In the years following the 2008 eruption, Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations indicate that Okmok has inflated at a variable rate of 40–195 mm/yr. In this study, we investigate the post‐eruptive deformation of Okmok (2008–2020) using InSAR and GNSS. L‐band ALOS‐2, C‐band Sentinel‐1/Envisat and X‐band TerraSAR‐X data are analyzed with Persistent Scatterer (PS) InSAR method. The deformation time series calculated from InSAR and GNSS are assimilated into finite element models using the Ensemble Kalman Filter to track the evolution of the magma system through time. The results indicate that the InSAR‐derived deformation history can be well explained by a spatially stable magmatic source located in the central caldera, at about 3 km beneath the sea level, which is also believed to be the same source that produced the 1997 and 2008 eruptions. Magma accumulation in the reservoir is about from 2008 to 2020, which is about 160% and about 60% of the total reservoir volume changes during the 1997 and the 2008 eruptions, respectively.

Spatiotemporal analysis of seismic velocity changes at Okmok volcano, Alaska and implications from deformation source modeling

In this study, we use ambient noise interferometry to determine temporal changes in seismic velocity at Okmok volcano, Alaska, during the inter-eruptive period between the 1997 and 2008 eruptions. Specifically, we examine seismic velocity changes between 2005 and 2007. We further calculate seismic velocity changes in the frequency and depth domains. Examination of depth-constrained changes in seismic velocity allow us to distinguish between volcanic and non-volcanic processes occurring at Okmok. We show evidence that the presence of overlying lava flows may result in long term increases in the seismic velocity of the subsurface. Using the software package Coulomb 3.3, complementary theoretical volumetric strain modeling of volcanic deformation at Okmok is also carried out. These strain models are interpreted in tandem with our depth-constrained changes in seismic velocity. This joint analysis technique allows us to determine the location of the volcanic deformation at Okmok during the 1997-2008 inter-eruptive period. The location technique that we develop requires the use of only three seismic stations or station pairs in order to locate the center of volcanic deformation. Thus, this technique is a potentially valuable tool for monitoring the location of active magma storage at sparsely instrumented volcanoes worldwide.

Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom

The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.

A post-eruption study of gases and thermal waters at Okmok volcano, Alaska

We report here on the first focused study of gas discharges and thermal spring waters at Okmok volcano since the 2008 phreatomagmatic eruptions. Results include the first compositional gas data from Okmok with minimal air contamination and the first data on magmatic carbon in Okmok spring waters. Chemical and isotopic analyses of the waters and gases are used to assess the character of Okmok fluids eight years after the eruptions ceased.Gases from vents on intracaldera Cone C have high concentrations of H2 and contain H2S rather than SO2, demonstrating the influence of a hydrothermal system, while isotope values of carbon (−10.2 to −8.9‰) and helium (~8 RA) confirm the presence of magma-derived volatiles. Estimates of equilibrium temperatures for the Cone C gas are ~230 ± 30 °C. A much cooler reservoir with a maximum temperature of ~55 °C feeds the intracaldera warm springs. Based on discharge measurements of creeks draining the caldera, the total heat output of the warm springs is estimated to be about 32 MW.Gas data from a single location of steaming ground at the Geyser Bight geothermal area southwest of the Okmok Caldera are given. The gas is typical of geothermal gases with high concentrations of H2S and an air-corrected helium isotope ratio of 7.15 RA.

Hindcasting Magma Reservoir Stability Preceding the 2008 Eruption of Okmok, Alaska

AbstractVolcanic eruptions pose a significant and sometimes unpredictable hazard, especially at systems that display little to no precursory signals. For example, the 2008 eruption of Okmok volcano in Alaska notably lacked observable short‐term precursors despite years of low‐level unrest. This unpredictability highlights that direct monitoring alone is not always enough to reliably forecast eruptions. In this study, we use the Ensemble Kalman Filter (EnKF) to produce a successful hindcast of the Okmok magma system in the lead up to its 2008 eruption. By assimilating geodetic observations of ground deformation, finite element models track the evolving stress state of the magma system and evaluate its stability using mechanical failure criteria. The hindcast successfully indicates an increased eruption likelihood due to tensile failure weeks in advance of the 2008 eruption. The effectiveness of this hindcast illustrates that EnKF‐based forecasting methods may provide critical information on eruption probability in systems lacking obvious precursors.

Oscillatory nature of the Okmok volcano's deformation

The time-dependent deformation of volcanic edifices can help one understand the dynamics of pre-eruptive overpressure build-up in magma chambers. Thus, geodetic time series recorded at the Okmok volcano, in Alaska, show a pattern of fast and short inflations — referred to as “pulses” — followed by either slower and longer deflations, or time intervals with no deformation. This pattern is superimposed onto a longer-period inflation. A rapid inflation occurred just before the 2008 eruption, which suggests that the underlying process may lead to eruptions. It is crucial to understand whether such a behavior is driven by external forcing, such as melt supply variations, or whether it can develop spontaneously within the volcano's plumbing system. Here we model the observed oscillations (2004–2008) as resulting from the hydraulic interaction between two shallow magma chambers fed by a deeper source region, a geometry that is consistent with geochemical, petrological, and geophysical data. The model shows that episodes of periodic fast inflations occur (i) when a viscosity gradient is present in the vertical pipe, for instance as the result of a temperature gradient; and (ii) when the flux supplying the shallower chamber lies between two bounds that we derive analytically. The deformation pulses observed at Okmok can, therewith, be fully explained by the internal variability of the magmatic system and do not require time-variable external forcing. The proposed model can also be seen as an improvement upon the classic hydraulic models regularly used to explain a commonly observed pattern of volcanic deformations, i.e. exponential inflation.

Widespread tephra layers in the Bering Sea sediments: distal clues to large explosive eruptions from the Aleutian volcanic arc

Tephra layers within marine sediments provide information on past explosive eruptions, which is especially important in the case of remote island arcs where data on proximal pyroclastic deposits can be scarce. Three Alaska-Aleutian tephras (labeled Br2, SR2, and SR4) were found in the late Pleistocene-Holocene sediments of the Bering Sea (north Pacific). We fingerprint glass from these tephras with the help of single-shard electron microprobe and LA-ICP-MS analyses and provide microprobe data on minerals from two of these tephras. The large compositional variability of the Alaska-Aleutian volcanoes permits the use of ratios of highly incompatible trace elements (Ba/Nb, Th/Nb, Th/La, La/Nb) for identification of distal tephra sources by comparison of these ratios in tephra glass and proximal bulk rock analyses. This method, along with mapped tephra dispersal, has allowed us to link tephras under study to Aniakchak, Semisopochnoi, and Okmok volcanoes, respectively. Our results indicate that tephra Br2 was derived from the ~ 3.6 ka Aniakchak II caldera-forming eruption (Alaska, USA). This is the first ever finding of the Aniakchak II tephra in Bering Sea sediments, which permits enlargement of its tephra volume and eruption magnitude to ~ 100 km3 and 6.8, respectively. Tephra SR2, dated at ~ 12.2 ka, is likely associated with a post-glacial caldera on the Semisopochnoi Island, Aleutians (USA). Tephra SR4 (dated at ~ 64.5 ka), likely was derived from an earlier undocumented eruption from Okmok volcano (Aleutians). All three regionally spread tephra layers are valuable isochrones, which can be used for correlating and dating of Bering Sea sediments.

Multiridge Method for Studying Ground-Deformation Sources: Application to Volcanic Environments

Volcanic phenomena are currently monitored by the detection of physical and chemical observations. Generally, the ground deformation field is the most relevant shallow expression of the geometric and physical parameters variations in the magmatic reservoir. In this study, we propose a novel method for the direct estimation of the geometric parameters of sources responsible for volcanic ground deformation detected via the DInSAR technique. Starting with the biharmonic properties of the deformation field, we define an approach based on the Multiridge and ScalFun methods to achieve relevant information about both the positions and shapes of active sources, such as the Mogi source. Our methodology is definitely different from the methods currently used for modeling ground-deformation sources, mainly based on forward or inverse techniques. In fact, (i) it does not require any assumptions about the source type, and (ii) it is not influenced by the distribution of medium elastic parameters or (iii) the presence of high-frequency noise in the dataset. For synthetic cases, we accurately estimate the depth to the source within a 3% error. Finally, we study the real case of the Okmok volcano ground-deformation field and achieve results compatible with those in previous works.

A45 Alaska, Okmok 火山における膨張レートのゆらぎ

A45 Alaska, Okmok 火山における膨張レートのゆらぎ

B12 GPS 観測によるアリューシャン列島オクモク火山における地殻変動(2000 年 8 月-2001 年 8 月)

B12 GPS 観測によるアリューシャン列島オクモク火山における地殻変動(2000 年 8 月-2001 年 8 月)

Graph theory for analyzing pair-wise data: application to geophysical model parameters estimated from interferometric synthetic aperture radar data at Okmok volcano, Alaska

Graph theory is useful for analyzing time-dependent model parameters estimated from interferometric synthetic aperture radar (InSAR) data in the temporal domain. Plotting acquisition dates (epochs) as vertices and pair-wise interferometric combinations as edges defines an incidence graph. The edge-vertex incidence matrix and the normalized edge Laplacian matrix are factors in the covariance matrix for the pair-wise data. Using empirical measures of residual scatter in the pair-wise observations, we estimate the relative variance at each epoch by inverting the covariance of the pair-wise data. We evaluate the rank deficiency of the corresponding least-squares problem via the edge-vertex incidence matrix. We implement our method in a MATLAB software package called GraphTreeTA available on GitHub (https://github.com/feigl/gipht). We apply temporal adjustment to the data set described in Lu et al. (Geophys Res Solid Earth 110, 2005) at Okmok volcano, Alaska, which erupted most recently in 1997 and 2008. The data set contains 44 differential volumetric changes and uncertainties estimated from interferograms between 1997 and 2004. Estimates show that approximately half of the magma volume lost during the 1997 eruption was recovered by the summer of 2003. Between June 2002 and September 2003, the estimated rate of volumetric increase is (6.2 , pm , 0.6) times 10^6~mathrm{m}^3/mathrm{year} . Our preferred model provides a reasonable fit that is compatible with viscoelastic relaxation in the five years following the 1997 eruption. Although we demonstrate the approach using volumetric rates of change, our formulation in terms of incidence graphs applies to any quantity derived from pair-wise differences, such as range change, range gradient, or atmospheric delay.

Volcano deformation source parameters estimated from InSAR: Sensitivities to uncertainties in seismic tomography

AbstractThe eruption cycle of a volcano is controlled in part by the upward migration of magma. The characteristics of the magma flux produce a deformation signature at the Earth's surface. Inverse analyses use geodetic data to estimate strategic controlling parameters that describe the position and pressurization of a magma chamber at depth. The specific distribution of material properties controls how observed surface deformation translates to source parameter estimates. Seismic tomography models describe the spatial distributions of material properties that are necessary for accurate models of volcano deformation. This study investigates how uncertainties in seismic tomography models propagate into variations in the estimates of volcano deformation source parameters inverted from geodetic data. We conduct finite element model‐based nonlinear inverse analyses of interferometric synthetic aperture radar (InSAR) data for Okmok volcano, Alaska, as an example. We then analyze the estimated parameters and their uncertainties to characterize the magma chamber. Analyses are performed separately for models simulating a pressurized chamber embedded in a homogeneous domain as well as for a domain having a heterogeneous distribution of material properties according to seismic tomography. The estimated depth of the source is sensitive to the distribution of material properties. The estimated depths for the homogeneous and heterogeneous domains are 2666 ± 42 and 3527 ± 56 m below mean sea level, respectively (99% confidence). A Monte Carlo analysis indicates that uncertainties of the seismic tomography cannot account for this discrepancy at the 99% confidence level. Accounting for the spatial distribution of elastic properties according to seismic tomography significantly improves the fit of the deformation model predictions and significantly influences estimates for parameters that describe the location of a pressurized magma chamber.

Water-magma interaction and plume processes in the 2008 Okmok eruption, Alaska

Eruptions of similar explosivity can have divergent effects on the surroundings due to differences in the behavior of the tephra in the eruption column and atmosphere. Okmok volcano, located on Umnak Island in the eastern Aleutian Islands, erupted explosively between 12 July and 19 August 2008. The basaltic andesitic eruption ejected ∼0.24 km3 dense rock equivalent (DRE) of tephra, primarily directed to the northeast of the vent area. The first 4 h of the eruption produced dominantly coarse-grained tephra, but the following 5 wk of the eruption deposited almost exclusively ash, much of it very fine and deposited as ash pellets and ashy rain and mist. Meteorological storms combined with abundant plume water to efficiently scrub ash from the eruption column, with a rapid decrease in deposit thickness with distance from the vent. Grain-size analysis shows that the modes (although not their relative proportions) are very constant throughout the deposit, implying that the fragmentation mechanisms did not vary much. Grain-shape features consistent with molten fuel-coolant interaction are common. Surface and groundwater drainage into the vents provided the water for phreatomagmatic fragmentation. The available water (water that could reach the vent area during the eruption) was ∼2.8 × 1010 kg, and the erupted magma totaled ∼7 × 1011 kg, which yield an overall water:magma mass ratio of ∼0.04, but much of the water was not interactive. Although magma flux dropped from 1 × 107 kg/s during the initial 4 h to 1.8 × 105 kg/s for the remainder of the eruption, most of the erupted material was ejected during the lower-mass-flux period due to its much greater length, and this tephra was dominantly deposited within 10 km downwind of the vent. This highlights the importance of ash scrubbing in the evaluation of hazards from explosive eruptions.

Post-Eruptive Inflation of Okmok Volcano, Alaska, from InSAR, 2008–2014

Okmok, a ~10-km wide caldera that occupies most of the northeastern end of Umnak Island, is one of the most active volcanoes in the Aleutian arc. The most recent eruption at Okmok during July–August 2008 was by far its largest and most explosive since at least the early 19th century. We investigate post-eruptive magma supply and storage at the volcano during 2008–2014 by analyzing all available synthetic aperture radar (SAR) images of Okmok acquired during that time period using the multi-temporal InSAR technique. Data from the C-band Envisat and X-band TerraSAR-X satellites indicate that Okmok started inflating very soon after the end of 2008 eruption at a time-variable rate of 48–130 mm/y, consistent with GPS measurements. The “model-assisted” phase unwrapping method is applied to improve the phase unwrapping operation for long temporal baseline pairs. The InSAR time-series is used as input for deformation source modeling, which suggests magma accumulating at variable rates in a shallow storage zone at ~3.9 km below sea level beneath the summit caldera, consistent with previous studies. The modeled volume accumulation in the six years following the 2008 eruption is ~75% of the 1997 eruption volume and ~25% of the 2008 eruption volume.

Monitoring changes in seismic velocity related to an ongoing rapid inflation event at Okmok volcano, Alaska

AbstractOkmok is one of the most active volcanoes in the Aleutian Arc. In an effort to improve our ability to detect precursory activity leading to eruption at Okmok, we monitor a recent, and possibly ongoing, GPS‐inferred rapid inflation event at the volcano using ambient noise interferometry (ANI). Applying this method, we identify changes in seismic velocity outside of Okmok's caldera, which are related to the hydrologic cycle. Within the caldera, we observe decreases in seismic velocity that are associated with the GPS‐inferred rapid inflation event. We also determine temporal changes in waveform decorrelation and show a continual increase in decorrelation rate over the time associated with the rapid inflation event. The magnitude of relative velocity decreases and decorrelation rate increases are comparable to previous studies at Piton de la Fournaise that associate such changes with increased production of volatiles and/or magmatic intrusion within the magma reservoir and associated opening of fractures and/or fissures. Notably, the largest decrease in relative velocity occurs along the intrastation path passing nearest to the center of the caldera. This observation, along with equal amplitude relative velocity decreases revealed via analysis of intracaldera autocorrelations, suggests that the inflation source may be located approximately within the center of the caldera and represent recharge of shallow magma storage in this location. Importantly, there is a relative absence of seismicity associated with this and previous rapid inflation events at Okmok. Thus, these ANI results are the first seismic evidence of such rapid inflation at the volcano.

J.F. Larsen, C.A. Neal, J.R. Schaefer, A.M. Kaufman, and Zhong Lu: The 2008 phreatomagmatic eruption of Okmok volcano, Aleutian Islands, Alaska: chronology, deposits, and landform changes

This book provides a detailed description of the spectacu-lar, 5-week long, 2008 eruption at Okmok volcano (VEI ≤4),located on Umnak Island, in the central Aleutian volcanic arc(Black 1975; Miller and Smith 1987; Burgisser 2005). It is avery good example of successful joint effort within a geolog-ical survey during an eruption-response, not only providingone of the most complete documentations of historicalphreatomagmatic eruptions, but also illustrating the complex-ity of such events and their strong impacts on local sedimen-tation rates, landscape variations, vent dynamics, and thehydrogeological setting.Phreatomagmatic and phreatic explosions are not rare inthe life span of any volcano, but they are commonlyoverlookedbecauseoftheirsmall-sizeandrapiderosioncom-paredtoothervolcanicproducts.Sincetheyarequitecommonin the current volcanic activity worldwide, difficulties ariseduringeruptionresponsesbecauseofthelackofreportsavail-able for comparison, as well as the scarcity and discontinuityof related deposits in the geological record. Therefore, thedescriptions presented in this book provide excellent refer-ences for a better understanding of these short-lived, but lo-cally hazardous events.Okmok’s Report of Investigations 2015 –2iscomplemen-tary to other on-going publications, which are referred tothroughout the text. It is aimed largely at the professionalgeologist but because of its wealth of superb illustrations incolor,itcouldbeappreciatedbyvolcanologyamateurs,andbyother scientists interested in extremely rapid landscape evolu-tion due to volcanism. Furthermore, the free access to thebook in pdf format, and the supplementary dataset, providean excellent opportunity to gain a wide audience and serve asan important reference source for future comparative studies.Chapter 1 gives an introduction to the 2008 eruption,pointing out the onset of dramatic changes in the local geo-morphology caused by the opening explosions, the multiplic-ity of syn-eruptivevents,and the lackof clear seismic precur-sors, the latter of which make phreatomagmatic events