Located at the junction of Kamchatka and the Aleutian Arc, the Klyuchevskoy Volcanic Group is arguably the most active island arc volcanic center in the world. Frequent and violent eruptions of its member volcanoes present both an immediate hazard to trans-Pacific air traffic and may have long-term climate implications. Ash from erupting Klyuchevskoy Group volcanoes has been tracked for thousands of miles away from Kamchatka and presents a serious threat to jet engines at high altitudes. Input of large volumes of volcanic ash into the atmosphere has been shown to impact global climate, causing multiple years of depressed temperatures following large eruptions. Yet, despite representing one of the largest volcanic features on the planet, the geodynamic mechanism to drive activity of the Klyuchevskoy Group is poorly understood. When the activity, size and position of the Klyuchevskoy Group is considered in the framework of regional tectonics it becomes apparent that this volcanic cluster simply can not exist in its present form. The position of the Klyuchevskoy relative to the subducting Pacific greatly exceeds typical depths of melt generation for arc volcanoes, and it is not clear where the lavas erupting at the Klyuchevskoy Groups are generated. This projects aims to put new seismological and geochemical constraints on the upper mantle structure beneath the Klyuchevskoy Group and shed light on the mechanism driving volcanic activity at this volcanic center. It is motivated by our previous research effort which identified anomalous feature in the upper mantle beneath the Klyuchevskoy Group which we believe holds the key to understanding the mechanism driving activity of this volcanic center.
We propose a detailed investigation of the anomaly we have identified within the mantle wedge beneath the Klyuchevskoy Group, coupled with an effort to relate geochemical tracers present in Klyuchevskoy Group lavas to the proposed seismic feature. The seismic study will utilize new data acquired in the framework of the ongoing NSF Partnership in Researh and Education (PIRE) effort in Kamchatka. We will use different types of teleseismic receiver function analysis to investigate the mantle wedge beneath the Klyuchevskoy Group. In parallel we will assemble a comprehensive database of geochemical information on KG lavas, using databases, published literature and emerging results from ongoing work. The ultimate goal of the project is to develop a geodynamic scenario for the Klyuchevskoy Group, informed by the seismic structure of the mantle wedge beneath it, and the geochemistry of lavas it produces.
This project is supported by the Geophysics and Petrology & Geochemistry Programs.
The research target of this project was the spectacular and enigmatic volcano called Klyuchevskoy, in Kamchatka (Russia). It occupies a special place in the Pacific Ring of Fire: sitting at the junction of Kamchatka and the Aleutian island chain, it is very large (nearly 5 km high), very young (less than 8 thousand years old), and extremely vigorous. By some calculations it is the most productive volcano of its kind in the world. Understanding the mechanisms of magma formation and eruption that sustain this volcano is an important goal for volcanology. Knowing about an extreme case offers insight into the rules that govern all "arc" volcanoes (that is, volcanoes formed when tectonic plates collide, one descends into the interior of the Earth and delivers volatiles, such as water, to great depth, where they promote melting of the hot rock). We investigated the distribution of seismic wave speed beneath Klyuchevskoy, using observations of elastic (seismic) waves from distant earthquakes. Speed of seismic waves is linked to temperature and chemical composition of the material they go through, and thus changes in it help understand the structure inside the Earth. Also, we re-evaluated depths of earthquakes happening close to and beneath this volcano. We also studied chemical compositions of lavas erupted by Klyuchevskoy and neighboring volcanoes, both active and extinct. Some of the seismic data were collected by Alex Nikulin, a graduate student whose PhD work was partially supported by the grant, while others came from the archives of the Kamchatka Branch of the Geophysical Service of Russian Academy of Sciences. Geochemical analyses relied on published databases of previously collected rock samples. We found an unusual body with low seismic wave speed at ~100 km depth beneath Klyuchevskoy. Its planar shape, and especially the fact that its boundaries are very sharply delineated, suggest chemistry rather than temperature as the main factor in seismic speed change. We interpreted this feature as a volume where melts of pyroxenite, a rock present in the upper mantle of the Earth concentrate prior to their eruption via the Klyuchevskoy volcano and smaller neighboring volcanoes. A systematic south-to-north change in the chemistry of lavas erupting from volcanoes around Klyuchevskoy, with those to the north of it showing a larger contribution from pyroxenite melts, appears consistent with the fact that the "slow" anomaly we detect with seismic waves is shallower to the north. Comparing depths of small earthquakes beneath Klyuchevskoy with seismological constraints on the thickness of Earthâ€™s crust beneath it, we established the fact of seismic activity in the uppermost mantle, an unusual condition for a volcano of this type. Chemical composition of lavas erupted from Klyuchevkoy volcano was used to evaluate the depth at which solid rocks of the upper mantle have melted to produce these lavas. We found good agreement in depths of earthquakes and depths of melt formation, and developed a scenario for a seismically active magma chamber – a volume beneath the volcano where formation and migration of melt is so vigorous that surrounding rocks are breaking, as evidences by earthquakes. Over the course of its existence, this grant supported in part the research work of two graduate students, Alex Nikulin and Maxim Gavrilenko. A vigorous collaborative effort with researchers of the Russian Academy of Sciences Geophysical Service in Kamchatka lead to data exchange and joint publications. Three Rutgers University undergraduates (Jennifer Geoghegan, Benjamin Dunham and Laura Sammon) participated in the work in research assistant capacity.