Research Objectives:
Magmatism is one of the most fundamental dynamic processes of planetary interiors, yet knowledge of the time-dependent parameters of basalt petrogenesis (solid mantle upwelling rate, melting rate, melt transport rate, magma storage time, and magma recharge rate) is quite limited. Magmatic processes such as melting, fractional crystallization, and magma chamber replenishment can fractionate parent/daughter ratios of U-decay series isotopes and thus create isotopic disequilibrium. Because the half-lives of U-series isotopes are comparable to the time scales of these processes, measurement of this isotopic disequilibrium in volcanic gases and mineral separates provides constraints on the duration and rates of magmatic processes.
Mount Erebus on Ross Island is Antarctica's most active volcano and also the only one with a persistent convecting lake of molten, alkali-rich phonolitic magma in its summit crater. This makes Mount Erebus one of the few volcanoes on Earth with nearly continuous, small explosive activity (two to six Strombolian eruptions daily) and continuous internal earthquake (seismic) activity. As such, it provides the ideal natural laboratory to study certain phenomena, specifically how gas is given off by magma and the seismic activity that results from a convecting magma conduit.
The small Strombolian eruptions eject volcanic bombs, thus providing samples of the magma with large, well-formed crystals. These bombs, plus older radiometrically dated lava flows around the summit of Mount Erebus, provide samples that constitute a unique opportunity to understand the timing of fundamental magmatic and volcanologic processes.
Researchers intend to combine seismic studies and gas emission rate measurements in order to elucidate the nature and dynamics of the magmatic plumbing system, as well as eruptions and degassing from the lava lake. (The eruptions will be captured on video.) The gas studies will provide some of the first data available on carbon dioxide degassing from a highly alkalic magma system. They should also help evaluate how much lead from Mount Erebus (relative to lead released by marine aerosols) gets into the snow on the East Antarctic Ice Sheet and thus shed light on hypotheses about the anthropogenic origins of lead. Further goals of the gas studies are to
• Examine the role of Mount Erebus as a source of gas and aerosols for the antarctic environment
• Understand the role of volcanism as a source of carbon dioxide emissions into the atmosphere, especially for highly alkalic magma
• Understand the evolution of the main volatile substances (water vapor, carbon dioxide, total sulfur, fluorine, and chlorine) in the Mount Erebus magmatic system, as well as their role in the eruptive behavior of the mountain
• Correlate the nature of the gas emissions with the observed seismic activity.
For the seismic studies, project team members will install five integrated scientific instrument packages, all slightly different, depending on their location. All will include a broadband seismometer and dual-frequency global positioning system (GPS) units with 900 mega-Hertz spread spectrum transceivers to telemeter the data to McMurdo Station. Other equipment will include tiltmeters, infrasonics sensors, meteorological instruments (wind speed and directions, pressure and temperature), infrared radiometers (thermometers), and gas sensors. The packages will be battery powered and have solar panels and wind generators. Researchers will also use GPS geodetic measurements for deformation studies to monitor the movement of magma inside the volcano.
Using U-series isotopes will allow researchers to examine the time scales of
• Magma genesis and melt transport from the mantle
• Magma evolution and crystallization processes during magma storage in the crust, and
• Magma degassing and recharge rates into the erupting magma chamber.
This is the first time U-series isotopes have been used in an integrated fashion to examine both gases and the associated magma. Researchers hope to achieve a better understanding of the whole magmatic system, from magma formation by partial melting in the mantle through its evolution and finally to its degassing and open-system behavior in the lava lake.
The resulting data should enhance the collection of earthquakes that researchers are using in a computer model of the interior of the volcano, as well as provide a tool that scientists can use for conducting volcano surveillance, monitoring eruptions, and detecting subtle changes in the internal behavior of volcanoes. The broadband data will support a detailed study of the explosion mechanism, especially the very-long-period signals that are emitted. It should also help reveal temporal and spatial variability in earthquake mechanisms, which in turn might provide more insights into how variations in gas emissions could be implicated.
