Kizimen Volcano Research Articles

Identification of tephra horizons in a glacier on the Ushkovsky volcano (Kamchatka)

Identification of tephra and its allocation (association) with known eruptive events allows obtainng chronostratigraphic markers, on the basis of which an age scale for dating glacial strata can be developed. To determine the sources of ash in the ice core obtained in 2022 during drilling of glacier in the crater of the Ushkovsky volcano in Kamchatka, the chemical composition of volcanic glass in individual ash particles was analyzed. The accuracy of determination of the volcanic glass composition was verified by analyzing of international standard samples of volcanic and synthetic glass. Based on a comparison of the data we obtained with published data on the composition of tephra glasses from the present-day eruptions in Kamchatka, we determined affiliation of each tephra horizon to specific volcano-source. We have found that the main source of tephra in the ice core of the Ushkovsky Glacier is the Kliuchevskoi volcano, which is the closest and the most productive one among the Kamchatka volcanoes. Ash particles from Bezymyannyi volcano were identified in two horizons. A mixed population of particles was found in one of the horizons, including the ash particles from volcanoes Kizimen, Kliuchevskoi and Bezymyannyi. Analysis of published data on the chronology and distribution of ash plumes from known eruptive events made it possible to confidently correlate the tephra horizon at a depth of 762–777 cm with the initial phase of the eruption of the Kizimen volcano in late 2010–early 2011. Ash from the uppermost tephra buried in the glacier at depths of 89–94 cm belongs to the Bezymyannyi volcano eruption, which the most likely occurred in October 2020. Single particles with rhyolitic composition of glass in the sample from the depth of 348–354 cm may belong to the eruption of the Shiveluch volcano in December 2018. The results of our work can be used on further studying of the ice core from the Ushkovsky volcano, in particular for comparison and correlation with the chronostratigraphic data obtained by glacio-chemical and isotope methods.

SEISMICITY of the VOLCANIC AREAS of KAMCHATKA in 2018–2019

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and the ash clouds. Daily information about volcanic activity is published in the Internet (http://www.emsd.ru/ ~ssl/monitoring/main.htm) since February 2000. The results of seismic activity of the Northern (Shiveluch, Kluchevskoy, Bezymianny, Krestovsky and Ushkovsky), Avacha (Avachinsky and Koryaksky), MutnovskyGorely volcano group and Kizimen, Zhupanovsky, Karymsky and Kambalny volcanoes for 2018–2019 are presented. Within two years 29199 earthquakes with KS=1.6–10.1 were located for Northern volcano group, 714 earthquakes with KS=1.6–7.6 – for Avacha volcano group, 247 earthquakes with KS=1.7–7.3 – Mutnovsky-Gorely volcano group, 116 earthquakes with KS=2.6–8.7 for Kizimen volcano, 315 earthquakes with KS=2.2–10.9 for Zhupanovsky volcano, five earthquakes with KS=6.2–8.3 for Kambalny volcano and four earthquakes with KS=5.2–6.7 for Karymsky volcano. Maps of epicenters, quantities of seismic energy and earthquake distribution according to class are given. All periods of activity were fixed and investigated by remote methods in 2018–2019: intensive volcanic activity of Sheveluch volcano associated with new cone, two paroxysmal explosive eruptions of Bezymianny volcano and the summit explosive-effusive eruptions of Kluchevskoy volcano.

НИЖНЕ-ЩАПИНСКИЕ ТЕРМАЛЬНЫЕ ИСТОЧНИКИ (КАМЧАТКА), КАК ПРИМЕР МАГНИЕВЫХ УГЛЕКИСЛЫХ ВОД

The results of hydrochemical studies of Nizhne-Shapinsky (Kipely) CO2-rich thermal (39 °C) springs in 2021 are presented. The springs discharge within the Shchapina graben near active Kizimen volcano. Results include macro- and trace-component composition, isotopic composition of spring water, some gas components and dissolved strontium. The results are discussed using previously published and reported data, taking into account the geological and structural setting of the area, water-rock interactions, and simple thermochemical calculations to explain the rare, but typical for the chemical composition of some CO2-rich waters, predominance of magnesium over calcium. It is shown that waters of Nizhne-Shchapinsky springs are formed as a result of mixing of two components: deeper and more heated sodium chloride water and more superficial, less heated water of Mg-Ca-HCO3- composition, formed due to interaction with carbonate-bearing rocks and CO2 of magmatic origin.

Multiplets of low-frequency earthquakes during the eruption of the Kizimen volcano in 2011–2012, Russia

Multiplets of low-frequency earthquakes during the eruption of the Kizimen volcano in 2011–2012, Russia

SEISMISITY of the VOLCANIC AREAS of KAMCHATKA in 2016–2017

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and the ash clouds. Daily information about volcanic activity is published in the Internet (http://www.emsd.ru/~ssl/monitoring/main.htm) since February 2000. The results of seismic activity of the Northern (Shiveluch, Kluchevskoy, Bezymianny, Krestovsky and Ushkovsky), Avacha (Avachinsky and Koryaksky), Mutnovsky-Gorely volcano group and Kizimen volcano for 2016–2017 are presented. Within two years 8152 earthquakes with KS=1.6–8.5 were located for Northern volcano group, 616 earthquakes with KS=1.6–7.2 – for Avacha volcano group, 357 earthquakes with KS=2.0–6.2 – Mutnovsky-Gorely volcano group, 144 earthquakes with KS=2.3–9.4 for Kizimen volcano, 322 earthquakes with KS=1.8–8.1 for Zhupanovsky volcano and 90 earthquakes with KS=5.0–8.6 for Kambalny volcano. Maps of epicenters, quantities of seismic energy and earthquake distribution according to class are given. All periods of activity were fixed and investigated by remote methods in 2016–2017: intensive volcanic activity of Sheveluch volcano associated with new cone, the summit explosive-effusive eruption of Kluchevskoy volcano from April 2016 till September 2017, explosive activity of Zhupanovsky volcano and seismic preparation and volcanic eruption of Kambalny volcano observed for the first time in historical period.

Correlated petrology and seismicity indicate rapid magma accumulation prior to eruption of Kizimen volcano, Kamchatka

The increase in number and intensity of earthquakes during a pre-eruptive crisis is the main basis of seismic volcano monitoring. However, a strong understanding of how these seismic signals relate to magmatic processes in the magma plumbing systems prior to volcanic eruptions is crucial for these efforts. Here we compare the characteristics of a seismo-volcanic crisis prior to the 2010–2013 explosive-extrusive eruption of Kizimen volcano, Kamchatka with the timescales of processes in the magma plumbing system. These timescales are inferred from the numerical modelling of iron-magnesium intracrystalline interdiffusion in 88 zoned orthopyroxene crystals from dacites and silica-rich andesites collected after the eruption. We find that the eruptible magmas were assembled rapidly during a magma mixing process beginning around 1.5 years before the eruption, which is well correlated with the onset of the seismic crisis. We conclude that the observed seismic re-activation marked the onset of magma mixing and led to destabilization of the reservoir, followed by the eruption.

SEISMISITY of THE VOLCANIC AREAS of KAMCHATKA in 2015

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and the ash clouds. Annual results of seismic activity of the Northern (Shiveluch, Kluchevskoy, Bezymianny, Krestovsky, and Ushkovsky), the Avacha (Avachinsky, and Koryaksky), the Mutnovsky-Gorely volcano groups and the Kizimen volcano are presented. 5464 earthquakes with КS=1.8–8.1 were located for the Northern volcano group, 302 earthquakes with КS=1.7–5.7 – for the Avacha volcano group, 295 earthquakes with КS=2.1–6.8 for the Mutnovsky-Gorely volcano group, 462 earthquakes with КS=2.2–8.3 for Kizimen volcano, and 165 earthquakes with КS=2.5–8.4 for Zhupanovsky volcano in 2015. Maps of epicenters, quantities of seismic energy and earthquake distribution by energy classes are given. All periods of activity were fixed and investigated by remote methods in 2015: intensive volcanic activity of the Sheveluch volcano associated with a new cone; the summit explosive-effusive eruption of the Kluchevskoy volcano in January–April; and a continuation of seismic and volcanic activity of the Zhupanovsky volcano after 56-year quite period.

Features of the Kizimen Volcano area seismicity prior to and during the 2010–2013 eruption

After 82 years of dormancy, Kizimen Volcano in Kamchatka (Russia) produced its first eruption that was supported by seismological observations. The 2010–2013 eruption lasted about three years and was preceded by high rates of seismicity lasting more than one and a half years. In this study we conduct a time-space seismicity analysis and consider the dynamics of the b-value (the slope of the cumulative distribution function of magnitudes). It is shown that there was a constant increase in stress. Which ended with an earthquake with MLmax = 5.2 followed by an eruption. The eruption was characterized by explosive phases and the squeezing out of a very viscous lava flow in 2011–2012. A change from effusive activity to explosive following swarms of volcano-tectonic earthquakes was observed throughout the entire period of the eruption. This confirms the poor mixing of magma in the chamber under the Kizimen Volcano.

VOLCANOES OF KAMCHATKA

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and the ash clouds. Daily information about volcanic activity is published in the Internet (http://www.emsd.ru/~ssl/ monitoring/main.htm) since February 2000. Annual results of seismic activity of the Northern (Shiveluch, Klu-chevskoy, Bezymianny, Krestovsky and Ushkovsky), Avacha (Avachinsky and Koryaksky), Mutnovsky-Gorely volcano group and Kizimen volcano are presented. 4983 earthquakes with КS=2.1–8.7 were located for Northern volcano group, 469 earthquakes with КS=1.6–6.1 – for Avacha volcano group, 459 earthquakes with КS=1.9–6.1 – Mutnovsky-Gorely volcano group, 220 earthquakes with КS=2.4–8.5 for Kizimen volcano and 238 earthquakes with КS=2.5–8.4 for Zhupanovsky volcano in 2014. Maps of epicenters, quantities of seismic energy and earth-quake distribution according to class are given. All periods of activity were fixed and investigated by remote me-thods in 2014: intensive volcanic activity of Shiveluch volcano associated with new cone, a con-tinuation of the seismic and volcanic activity of Zhupanovsky volcano after 56-year quite period and the ending of the summit explosive-effusive eruption of Kluchevskoy volcano in January-February.

Estimating the Attenuation of Seismic Wave Energy at Short Distances from Kizimen Volcano, Kamchatka

A swarm of volcanic earthquakes that occurred during an eruption of Kizimen Volcano provided an opportunity to study the attenuation of seismic wave energy in volcanogenic rocks at short hypocentral distances from the volcano. The study is based on P and S waves, as well as coda waves, using frequency dependent and frequency independent methods: pulse broadening, code normalization, and the model of single backscattering of coda waves. It is possible that further studies along these lines would also yield results for stress and strain in volcanogenic rocks beneath the volcano and in its cone. The determination of intrinsic absorption and scattering of seismic waves showed that the total attenuation within the volcanic edifice is dominated by shear wave scattering compared with intrinsic energy absorption. The conclusion is that the Q of the Kizimen volcanogenic rocks is higher than that of tectonic media.

Сейсмический режим «drumbeats», обусловленный движением вязкого лавового потока при извержении вулкана Кизимен в мае-октябре 2011 г.

The “drumbeats” mode is a sequence of volcanic earthquakes with similar waveforms (multiplets) that are recorded from tens of minutes to months. As a rule, the “drumbeats” mode accompanies the squeezing of lava blocks on extrusive domes of andesite-dacite volcanoes. Squeezing and movement of a viscous lava flow during an eruption Kizimen volcano in 2010-2013 was accompanied by multiplets with energy classes K<6 (magnitudes < 2.5), which were recorded from tens of minutes to months. Two series of the strongest multiplets were recorded during the four months from May to mid-October 2011. The volcanic earthquakes of multiplets can be attributed to hybrid and long-period. The coordinates of the foci were identified for the most powerful 35 events of two multiplets of “drumbeats” mode and were localized in the frontal part of the lava flow. The location of the volcanic earthquakes hypocenters suggests that they are generated during the motion of a viscous lava flow the volcano slope. The emergence of multiplets, apparently, can be considered as a process of self-oscillations of the relaxation type.

ВУЛКАНЫ КАМЧАТКИ

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and ash clouds. Daily information about the volcanic activity is published on the Internet (http://www.emsd.ru/~ssl/monitoring/main.htm) since February 2000. Annual results of the seismic activity of the Northern (Shiveluch, Kluchevskoy, Bezymianny, Krestovsky, and Ushkovsky), Avacha (Avachinsky and Koryaksky), Mutnovsky-Gorely volcano group, and Kizimen volcano are presented. 4390 earthquakes with КS=3.0–8.5 were located for the Northern volcano group, 213 earthquakes with КS=1.8–5.7 – for Avacha volcano group, 110 earthquakes with КS=2.7–7.2 – Mutnovsky-Gorely volcano group, 199 earthquakes with КS=3.0–8.5 for Kizimen volcano, and 22 earthquakes with КS=3.7–6.7 for the Zhupanovsky volcano in 2013. Maps of epicenters, quantities of seismic energy, and earthquake distribution according to class are given. All periods of activity were fixed and investigated by remote methods in 2013: intensive volcanic activity of Sheveluch volcano associated with new cone, subplinian summit eruption of Kluchevskoy volcano, seismic and volcanic activity of Zhupanovsky volcano after a 56-year quite period, and the ending of the long-time eruptions: Tolbachik fissure eruption and Kizimen volcano eruption.

СЕЙСМИЧЕСКИЙ РЕЖИМ «DRUMBEATS», ПРЕДВАРЯЮЩИЙ И СОПРОВОЖДАЮЩИЙ ИЗВЕРЖЕНИЯ АНДЕЗИТОВЫХ И ДАЦИТОВЫХ ВУЛКАНОВ И ЕГО ОСОБЕННОСТИ (ОБЗОР)

During extrusive eruptions of andesitic and dacitic volcanoes, in some cases, squeezing of viscous lava was accompanied by the occurrence of «drumbeats» earthquakes. The peculiarities of this earthquake regime are: their close energies, similarity of wave forms, and quasi-periodicity over a long period of time (from several hours to months). The article provides an overview of the micro-earthquakes of the regime «drumbeats» recorded on several volcanoes of our planet during the extrusion of extrusive domes: Redout (the Aleutian Islands), St. Helens (the Cascade Mountains, North America), Soufriere Hills (Montserrat Island, the Lesser Antilles), Pichincha (the Andes, South America). During the eruption of Kizimen Volcano (Kamchatka Peninsula) in 2010–2013 the «drumbeats» mode was observed during the movement of a viscous lava flow. According to the record form, earthquakes of the «drumbeats» regime refer to hybrid or long-period earthquakes, with prevailing frequencies within the range of 0.3–7 Hz.

Deposits, petrology and mechanism of the 2010–2013 eruption of Kizimen volcano in Kamchatka, Russia

Kizimen volcano in Kamchatka is well known as a source of highly heterogeneous poorly mingled magmas ranging from dacites to basaltic andesites. In 2010–2013, the volcano produced its first historical magmatic eruption with the deposition of 0.27 km3 of block and ash pyroclastic flows accompanied by slow extrusion of a 200-m-thick, highly viscous (1010–1011 Pa s) block lava flow with a volume of 0.3 km3. The total volume of erupted magma comprised approximately 0.4 km3 DRE. We provide description of the eruption chronology, as well as the lithology and petrology of eruptive products. The erupted material is represented by banded dacite and high-silica andesite. The dacitic magma was formed during a long dormancy after the previous magmatic eruption several hundred years ago with mineral compositions indicating average pre-eruptive temperatures of ~ 810 °C, fO2 of 0.9–1.6 log units above the nickel–nickel oxide (NNO) buffer and shallow crustal storage conditions at ~ 123 MPa. The silica-rich andesite represents a hybrid magma, which shows signs of recent thermal and compositional disequilibrium. We suggest that the hybrid magma started to form in 1963 when a swarm of deep earthquakes indicated an input of mafic magma from depth into the 6–11-km-deep silicic magma chamber. It took the following 46 years until the magma filling the chamber reached an eruptible state. Poor mingling of the two melts is attributed to its unusually high viscosity that could be associated with the pre-eruptive long-term leakage of volatiles from the chamber through a regional tectonic fault. Our investigations have shown that shallow magma chambers of dormant volcanoes demonstrating strong persistent fumarolic activity can contain highly viscous, degassed magma of evolved composition. Reactivation of such magma chambers by injection of basic magma takes a long time (several decades). Thus, eruption forecasts at such volcanoes should include a possibility of long time lag between a swarm of deep earthquakes (indicating the recharge of basic magma from depth) and the following swarm of shallow earthquakes (indicating final ascent of the hybrid magma towards the surface). Due to the high viscosity of the magma, the shallow swarm can last for more than a year. The forthcoming eruption can be of moderate to low explosivity and include extrusion of viscous lava flows and domes composed of poorly mingled magmas of contrasting compositions.

Estimation of total discharges of volcanic ash using atmospheric-transport models

We propose a method for calculating the total mass and grain-size composition of the ash that enters the atmosphere during explosive eruptions based on direct numerical modeling of transport and precipitation of ash particles and measurements of deposited mass in the ashfall area. The solution reduces to an overdetermined problem in a single parameter, viz., discharge rate as estimated by least squares from the minimal prior information on wind field structure and discharge heights. The example we consider in this study is the explosive event of January 13, 2011 on Kizimen Volcano accompanied by emission of pyroclastic products to heights of 6–9 km a.s.l. with subsequent propagation of the downwind plume to distances on the order of a few hundred kilometers. The ultimate estimate for the emitted volume (0.68–1.67 million tons) is in overall agreement with calculations made using the isopach method along with the Fedotov nomogram based on data on the eruptive cloud height and wind velocity. It is shown that meso-scale (2–200 km) atmospheric disturbances above mountains exert the controlling influence on the conditions of transfer/deposition of ash particles; this influence should be taken into account in order to derive correct estimates for emission mass and the role of wind-caused gravity differentiation of ash material during the formation of volcanogenic deposits.

Seismicity observed during the precursory process and the actual eruption of Kizimen Volcano, Kamchatka in 2009–2013

Kizimen Volcano began to erupt in December 2010. The eruption was preceded by a precursory period of seismicity that lasted for 20 months. This paper discusses the space-time features of the precursory seismicity. We provide a brief description of this explosive and effusive eruption between December 2010 and March 2013. The eruption started with some explosive activity followed by extrusion of a viscous lava flow. The extrusion of viscous andesitic magma and the motion of the lava flow down the slope were accompanied by unusual seismicity in the form of the quasiperiodic occurrence of microearthquakes, the so-called drumbeat phenomenon. It is shown that the occurrence of a drumbeat was first recorded during the extrusion process at the volcano’s summit. Subsequently, the drumbeat mode of activity was caused by the front of the viscous lava flow as it was moving down the slope. The dynamic parameters of the microearthquakes varied in accordance with the dimensions of the lava flow front. The motion of the main tongue of the lava flow (March to September 2011) gave rise to drumbeat I with energy classes of microearthquakes K = 3–5.5, while the second tongue, which was smaller than the first, produced drumbeat II with microearthquakes of K < 3 during its motion down the slope. In January 2013 we saw a phenomenon similar to the drumbeat that was recorded at the start of the eruption. This was caused by an obelisk being extruded at the volcano’s summit.

The 2010–2012 eruption of Kizimen Volcano: The greatest output (from the data of remote-sensing observations) for eruptions in Kamchatka in the early 21st century part I. The November 11, 2010 to December 11, 2011 phase

This paper presents the results from the detailed analysis of aerial photographs and space images for the Kizimen area, which characterize the geologic and geomorphologic effects of the ongoing eruption over the 2010–2011 period. It is shown that the total volume (>0.5 km3) and total mass (>109 t) of the discharged (resurgent plus juvenile) material makes this eruption the most productive in Kamchatka for the first 12 years of the 21st century. The dominant component (>90%) is juvenile material with andesitic composition. The pyroclastics (tephra, deposits of the juvenile pyroclastic avalanches and incandescent debris avalanches) comprise >0.3 km3and >0.45× 109 t, the lava (a very thick block lava flow 3.052 km long and 2.163 km2 in area) occupies about 0.195 km3 and 0.45 × 109 t. With the exception of the tephra, which fell over an area of about 100000 km2, the rest of the material was accumulated on the Kizimen cone and at its base. The mean discharge rate of juvenile ejecta was about 15 m3/s (29 t/s) for 13 months (November 11, 2010 to December 11, 2011). Appreciable changes also occurred at the near-summit part of the volcano’s cone.

Infrasonic waves from volcanic eruptions on the Kamchatka peninsula

The IS44 station operates at the observation point of Nachiki on the Kamchatka peninsula, which is part of the International Monitoring System (IMS), and it helps verify compliance with the Comprehensive Nuclear Test-Ban Treaty (CTBT). The Kamchatka Branch, Geophysical Service, Russian Academy of Sciences (KB GS RAS), has a station operating in the village of Paratunka. Both of these stations allow one to monitor strong explosive eruptions of andesitic volcanoes.1 Both kinematic and dynamic parameters of acoustic signals accompanying the eruptions of the Bezymyannyi volcano (at a distance of 361 km from Nachiki) in 2009–2010 and the Kizimen volcano (at a distance of 275 km) on December 31, 2011, are considered. A low-frequency rarefaction phase 60 s in length has been revealed in the initial portion of the record of acoustic signals accompanying such strong eruptions. It is shown that the rarefaction phase occurs due to the rapid condensation of superheated juvenile vapor2 that enters the atmosphere during such explosions.3 The amount of volcanic ash emitted into the atmosphere has been estimated within (3.2–7.3) 106 m3 on the basis of acoustic signals recorded during the eruptions under consideration.

Major and trace element zoning in plagioclase from Kizimen Volcano (Kamchatka): Insights into magma-chamber processes

The data on the geochemistry of the rocks of Kizimen Volcano and results of microprobe studies of major and trace elements in plagioclase grains from acid lavas and basalt inclusions are presented. The characteristics of the Kizimen Volcano are the following: (1) basalt inclusions are abundant in acid lavas; (2) banded, mixed lavas occur; (3) the distribution curves of rare-earth elements of acidic lavas and basalt inclusions intersect; (4) Sr-Nd isotope systematics of the rocks and inclusions do not indicate mixture with crustal material; (5) plagioclase phenocrysts are of direct and reverse zonation; (6) olivine and hornblende, as well as acid and mafic plagioclases, coexist in the rocks. The studies revealed that the rocks are of a hybrid nature and originated in the course of repeated mixture of acid and mafic melts either with chemical and thermal interaction of melts or exclusively thermal ones. Study of the major- and trace-element distribution in zonal minerals provides an informative tool for understanding the history of the generation and evolution of melts in a magma chamber.

Pre-eruption deformation caused by dike intrusion beneath Kizimen volcano, Kamchatka, Russia, observed by InSAR

Interferometric synthetic aperture radar (InSAR) images reveal a pre-eruption deformation signal at Kizimen volcano, Kamchatka, Russia, where an ongoing eruption began in mid-November, 2010. The previous eruption of this basaltic andesite-to-dacite stratovolcano occurred in 1927–1928. InSAR images from both ascending and descending orbital passes of Envisat and ALOS PALSAR satellites show as much as 6cm of line-of-sight shortening from September 2008 to September 2010 in a broad area centered at Kizimen. About 20cm of opening of a nearly vertical dike provides an adequate fit to the surface deformation pattern. The model dike is approximately 14km long, 10km high, centered 13km beneath Kizimen, and strikes NE–SW. Time-series analysis of multi-temporal interferograms indicates that (1) intrusion started sometime between late 2008 and July 2009, (2) continued at a nearly constant rate, and (3) resulted in a volume expansion of 3.2×107m3 by September 2010, i.e., about two months before the onset of the 2010 eruption. Earthquakes located above the tip of the dike accompanied the intrusion. Eventually, magma pressure in the dike exceeded the confining strength of the host rock, triggering the 2010 eruption. Our results provide insight into the intrusion process that preceded an explosive eruption at a Pacific Rim stratovolcano following nearly a century of quiescence, and therefore have implications for monitoring and hazards assessment at similar volcanoes elsewhere.