The western United States has been the site of some of the largest and most hazardous volcanic events in the world. Two of these events occurred within the last million years: supervolcano eruptions at both Yellowstone, WY and Long Valley, CA. The magma that erupted is called high-silica rhyolite. To understand how high-silica rhyolite forms and then erupts in such large amounts, scientists need to study the structure of the underground magmatic systems that feed eruptions. Some minerals change their chemical make-up under different temperatures and pressures. That makes it hard to use their chemical composition to calculate at what temperatures and pressures those magmas formed. Experiments done in this study will help scientists more accurately find the temperatures and depths of magma beneath supervolcanoes. This will help improve our understanding of how these powerful eruptions occur, while training numerous students. During this project, a series of experiments (primarily at 200 and 500 MPa; 650-850°C) will be conducted on four natural high-silica (SiO2) rhyolites of varying titanium oxide (TiO2) content. The experiments will be focused on the temperature and pressure dependence to the partitioning of titanium (Ti) between (1) biotite and high-SiO2 rhyolite liquid and (2) quartz and high-SiO2 rhyolite liquid. Preliminary results indicate that Ti partitioning between biotite and melt has the potential to be a high-resolution thermometer in high-SiO2 rhyolite melts. Th