Date of Award

Winter 2019

Project Type


Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Julia G Bryce

Second Advisor

Joseph M Licciardi

Third Advisor

Sarah A Miller


Magma storage and assembly processes of large-scale volcanic systems such as Mount Mazama, the volcano that led to the caldera-forming eruption of Crater Lake, remain a topic of debate. Catastrophic eruptions from these volcanoes cause devastating effects on local environments and potentially disrupt larger, regions through the release of thousands of cubic kilometers of material. Understanding the mechanisms that fueled the Mount Mazama magmatic system prior to the climactic eruption of 7.7 ka may provide insight into supply systems of similar volcanoes and, accordingly, their potential for caldera-forming eruptions. Volcanic systems such as Mount Mazama are thought to harvest crystalline magmatic materials prior to large-scale eruptions (Burgisser and Bergantz, 2011). The dominant mode of storage of these materials can determine the physical characteristics of a magma chamber prior to eruption. Should the crystals be kept in a cold, rheologically locked-up state, rejuvenation and subsequent eruption could occur on a mere 10 to 1,000 year timescale (Cooper and Kent, 2014). Conversely, if the crystals had been kept in a predominantly warm environment then the magma chamber may display physical signs of low-viscosity, easily eruptible, magma for timescales greater than 100,000 years (Barboni et al., 2016). To ascertain the dominant mode of crystal storage prevalent in the mafic units of Red Cone and Castle Point of Mount Mazama, we carried out in situ investigations of minor elemental profiles orthopyroxene from these eruptive materials. LA-ICP-MS analyses of these crystals provided trace elemental concentration gradients that were then used, in concert with finite difference modeling, to infer timescales of storage within a warm environment from predicted diffusion gradients. Of the trace elements analyzed, chromium (Cr) provided the concentration gradients needed for effective diffusion modeling. Samples from the Red Cone eruptive unit, as well as some of the Castle Point orthopyroxene, did not bear concentration gradients outside of analytical uncertainty, and thus could not be used for diffusion analysis with these methods. However, all analyses lacked the trace element concentration gradients typical of a cold-storage environment. Orthopyroxene suitable for diffusion modeling from the Castle Point samples predicted timescales of storage within warm environments of 958 – 982 oC for a minimum of 20 ± 10 ka. These predicted timescales place the storage of Castle Point orthopyroxene outside the range of a cold-storage dominated system. Additionally, elevated Cr concentrations at the rims of these orthopyroxene suggest the presence of mafic recharge to the system. Together, these results suggest the storage of the Castle Point crystalline material under a predominantly warm-storage regime sustained by recharging mafic magmas.