Pavel E. Izbekov

Eruption of andesite triggered by dyke injection: contrasting cases at Karymsky Volcano, Kamchatka and Mt Katmai, Alaska

Arc volcanoes often erupt andesite that appears to have been stored in reservoirs at shallow depth for protracted periods. As crystal-rich andesite is close in density to upper crust, such storage may be quite stable. Petrological evidence, and occasionally geological and geophysical evidence as well, suggests that the immediate trigger for eruption of the stored magma is injection of new magma into the reservoir, presumably through dykes rising from depth. When the dyke magma is more mafic than the stored andesite, effusive eruption typically results. When the dyke magma is voluminous and more silicic, the results are catastrophic, with production of discontinuously zoned tephra deposits and caldera collapse. Contrasting end-members are illustrated by the eruptions of Karymsky Volcano in 1996 and of Mt Katmai in 1912.

Calcic cores of plagioclase phenocrysts in andesite from Karymsky volcano: Evidence for rapid introduction by basaltic replenishment

Calcic cores in plagioclase of Karymsky andesite of the 1996–2000 eruptive cycle texturally and compositionally (both trace and major elements) mimic the plagioclase phenocrysts of basalt erupted 6 km away at the onset of the cycle. These observations support the view that simultaneous eruption of andesite and basalt at Karymsky in the beginning of the cycle represents an example of replenishment and eruption triggering of an andesitic reservoir. Homogeneity of andesitic output occurred within two months. This suggests to us that blending of injected basalt into reservoir magma was thorough and rapid.

The 1997 eruption of Okmok Volcano, Alaska: a synthesis of remotely sensed imagery

Abstract Okmok Volcano, in the eastern Aleutian Islands, erupted in February and March of 1997 producing a 6-km-long lava flow and low-level ash plumes. This caldera is one of the most active in the Aleutian Arc, and is now the focus of international multidisciplinary studies. A synthesis of remotely sensed data (AirSAR, derived DEMs, Landsat MSS and ETM+ data, AVHRR, ERS, JERS, Radarsat) has given a sequence of events for the virtually unobserved 1997 eruption. Elevation data from the AirSAR sensor acquired in October 2000 over Okmok were used to create a 5-m resolution DEM mosaic of Okmok Volcano. AVHRR nighttime imagery has been analyzed between February 13 and April 11, 1997. Landsat imagery and SAR data recorded prior to and after the eruption allowed us to accurately determine the extent of the new flow. The flow was first observed on February 13 without precursory thermal anomalies. At this time, the flow was a large single lobe flowing north. According to AVHRR Band 3 and 4 radiance data and ground observations, the first lobe continued growing until mid to late March, while a second, smaller lobe began to form sometime between March 11 and 12. This is based on a jump in the thermal and volumetric flux determined from the imagery, and the physical size of the thermal anomalies. Total radiance values waned after March 26, indicating lava effusion had ended and a cooling crust was growing. The total area (8.9 km 2 ), thickness (up to 50 m) and volume (1.54×10 8 m 3 ) of the new lava flow were determined by combining observations from SAR, Landsat ETM+, and AirSAR DEM data. While the first lobe of the flow ponded in a pre-eruption depression, our data suggest the second lobe was volume-limited. Remote sensing has become an integral part of the Alaska Volcano Observatory’s monitoring and hazard mitigation efforts. Studies like this allow access to remote volcanoes, and provide methods to monitor potentially dangerous ones.

Comagmatic granophyre and dacite from Karymsky volcanic center, Kamchatka: experimental constraints for magma storage conditions

Abstract Despite a ∼30 000 years difference in age, two caldera-forming eruptions at Karymsky volcanic center, Kamchatka – Karymsky (7900 yr BP) and Academy Nauk (ca. 40 000 yr BP) – produced two-pyroxene dacites with the same composition and mineralogy. Granophyric xenoliths of the identical whole-rock chemistry were found in basalts erupted within Academy Nauk caldera in 1996. Unlike the dacites, however, the granophyres are holo-crystalline and contain biotite and amphibole. Large amphibole phenocrysts contain rare inclusions of clinopyroxenes, which compositionally overlap with clinopyroxenes in the dacites. The Al content of the amphibole suggests it grew at a pressure of about 100 MPa. Results of hydrothermal experiments and petrologic observations indicate that Academy Nauk and Karymsky dacites were last equilibrated at 883±19°C, 100±15 MPa and 871±19°C, 85±18 MPa, respectively, both at water-saturated conditions. The mineral assemblage of granophyre is reproduced by isobaric crystallization of the dacite at 100 MPa, implying that the granophyres were sampled from the crystallized silicic reservoir that produced the caldera-forming eruption of Academy Nauk. Similar chemical compositions of Karymsky and Academy Nauk dacites indicate that both were derived from the same crustal-level source. The eruptive history of the calderas can best be explained by two 10–12-km 3 dacitic batches that detached from a parental body situated in the lower crust, then ascended to 3–4 km depth, re-equilibrated, and erupted.

Lightning-induced volcanic spherules

Glass spherules have been documented in many geologic deposits and are formed during high-temperature processes that include cloud-to-ground lightning strikes, volcanic eruptions of low-viscosity magmas, and meteorite impacts. This study reviews the known glass spherule– forming processes and proposes, for the first time, a mechanism induced through the heat generated by volcanic lightning in eruptive columns and plumes (laterally spreading clouds) during explosive eruptions. Ash-fall samples were collected from two eruptions where volcanic lightning was extensively documented: the A.D. 2009 eruption of Mount Redoubt, Alaska (USA), and the 2010 eruption of Eyjafjallajokull, Iceland. These samples reveal individual glass spherules ~50 mm in average diameter that compose <5% of the examined portion of the deposit. Textures include smooth, hollow, or cracked spherules, as well as aggregates, which suggest melting of ash particles as a result of proximity to the electrical discharge channel and subsequent re-solidification of the particles into spherical morphologies. The natural ash-fall samples are compared with pseudo-ash samples collected from high-voltage insulator experiments in order to test our hypothesis that volcanic ash particles can be transformed into glass spherules through the heat generated by electrical discharge. We refer to this new morphological classification of ash grains as lightning-induced volcanic spherules and hypothesize that this texture not only provides direct physical evidence of lightning occurrence during explosive eruptions, but will also increase settling velocities and reduce aggregation of these particles, affecting ash transport dynamics.

Pre-eruptive storage conditions of the Holocene dacite erupted from Kizimen Volcano, Kamchatka

This study describes an investigation of the pre-eruptive conditions (T, P and fO2) of dacite magma erupted during the KZI cycle (12,000–8400 years ago) of Kizimen Volcano, Kamchatka, the earliest, most voluminous and most explosive eruption cycle in the Kizimen record. Hydrothermal, water-saturated experiments on KZI dacite pumice coupled with titanomagnetite-ilmenite geothermometry calculations require that the KZI dacite existed at a temperature of 823 ± 20°C and pressures of 125–150 MPa immediately prior to eruption. This estimate corresponds to a lithologic contact between Miocene volcaniclastic rocks and Pliocene-Pleistocene volcanic rocks located at a depth of 5–6 km beneath the Kizimen edifice, which may have facilitated the accumulation of atypically large volumes of gas-rich dacite during the KZI cycle.

Pre-eruptive magma mixing and crystal transfer revealed by phenocryst and microlite compositions in basaltic andesite from the 2008 eruption of Kasatochi Island volcano

Abstract The August 7-8, 2008, eruption of Kasatochi Island volcano, located in the central Aleutians Islands, Alaska, produced abundant, compositionally heterogeneous basaltic andesite (52-55 wt% SiO2) that has been interpreted to result from pre-eruptive magma mixing. The basaltic andesite contains two populations of plagioclase phenocrysts. The first, volumetrically dominant population consists of oscillatory-zoned phenocrysts with an overall normal zonation trend toward comparatively sodic rims (An55-65), interrupted by dissolution features and spikes in calcium content (up to ~An85). The second population consists of phenocrysts with highly calcic compositions (~An90). These phenocrysts contain sharp decreases in calcium content close to their rims (reaching as low as ~An60), but are otherwise texturally and compositionally homogeneous. Groundmass plagioclase microlites are generally much more calcic than rims of the first phenocryst population, with more than 50% of measured microlites containing >An80. Major, minor, and trace element concentrations of plagioclase microlites and phenocrysts indicate that oscillatory-zoned phenocrysts derived from cooler (800-950 °C), more silicic mixing magma, while unzoned, calcic phenocrysts were associated with hotter (900-1050 °C), mafic magma. The mixing of these magmas just prior to eruption, followed by decompression during the eruption itself created high effective undercoolings in the mafic end-member, and lead to the nucleation of high-An microlites. MgO and FeO concentrations of plagioclase microlites and high-An phenocryst rims (up to ~0.4 and ~1.3 wt%, respectively) provide further evidence for high mixing- and eruptioninduced effective undercoolings.

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.

Applications of high-resolution satellite remote sensing for northern Pacific volcanic arcs

There has been a dramatic increase in the remote-sensing data volume being acquired from Earth orbit over the past two decades. Although none of these satellite instruments were designed specifically to monitor volcanic eruptions, many government agencies and university partnerships are currently utilizing them for this task. Most rely on high temporal/moderate spatial resolution instruments (e.g., MODIS, AVHRR, GOES) to monitor transient and temporally variable anomalies such as eruption clouds and hot spots. The uses of these instruments for such purposes are detailed in Chapters 3, 4 and 6. However, in order to better develop a quantitative scientific basis from which to model transient geological and meteorological hazards as well as map small-scale phenomena, higher spatial/spectral resolution datasets are commonly needed. Whereas moderate-resolution data may be frequently received directly from the satellite at many institutes globally, access to, and temporal frequency of, coverage from high-resolution instruments has been limited because much of the data must be specially acquired and purchased using a few government (e.g., ASTER, ETM+) and commercial (e.g., IKONOS, QuickBird) providers. Despite this, high-resolution data use has increased greatly as their capabilities have become recognized. The data from these sensors are particularly useful for numerous aspects of volcanic remote sensing. For example, high spatial resolution/multispectral thermal infrared data are critical for monitoring low-temperature anomalies and mapping both chemical and textural variations on volcanic surfaces. The data can also be integrated into a near-real time monitoring effort that is based primarily on high temporal/moderate spatial resolution orbital data. This synergy allows small-scale activity to be targeted for science and response, and the establishment of a calibration baseline between each sensor. The focus of this chapter is to highlight how these high spatial resolution (<100 m/pixel) data, commonly with more spectral capabilities, are being used for volcanic mapping and monitoring in the North Pacific region. A review of volcanic remote-sensing research using these data is presented with attention paid to case studies of new research. These studies showcase the capabilities of higher resolution sensors to map pyroclastic flows and detect changes over time in those flows (Mt. Augustine Volcano), and to document detection of volcanic terrains using a fusion approach of data from the visible to the radar wavelengths (Westdahl Volcano).

Aleutian Arc Fluid Geochemical Data

This report contains the chemical and isotopic data from thermal waters and gases collected from the Aleutian Arc over the past 20 years, where such data remain unpublished or only published in part.