In the process of trying to determine when a volcano will erupt, the most difficult eruptions to predict are usually the most violent and explosive eruptions. While there was an obvious increase in activity surrounding Mount St. Helens prior to its eruption in 1980, due to its previous inactivity, the violent eruption and the cause for such explosivity was unknown. Similarly the Shiveluch eruption of 2001 in Kamchatka, Russia was equally unpredictable (Blundy et al. 76). Though this paper was not written to help predict the next explosive eruptions of these volcanoes, the authors did use samples from both of the previously mentioned eruptions to examine and better understand the variations in temperature due to the magma rising beneath the volcanoes themselves.
A few different methods can be used to help determine the temperature changes within the magma system. The method used in this paper was through the observation of plagioclase crystallization found in volcanic inclusions. By analyzing 99 and 50 melt inclusions from Mount St. Helens and Shiveluch respectively along with their adjacent plagioclases, Blundy et al. found that prior to eruption, the magma experienced a clear increase in temperature and crystallinity while also decreasing partial pressure of H2O (77). This is consistent with a rapid rise of the magma beneath the volcanic reservoir roughly 7km below the surface. It was found that this sub-volcanic magma experienced a temperature increase of up to 100°C and up to 40wt% increase in crystallinity (Blundy et al. 77). Once these temperature and crystallinity changes were known, the authors also ran calculations thermodynamically with assumed initial pressure and temperatures (78). With these calculations they were able to conclude that this magma was decompressing sufficiently slow enough to allow for unique crystallization within the matrix (Blundy et al. 78). Thus, they were able to demonstrate that consideration must be put into latent heat release when examining magmatic phenocryst texture and the subsequent models of magmatic movement below the surface on future eruptions of the volcano (Blundy et al. 79).
- Blundy, Jon, Cashman, Kathy, Humphreys, Madeline. “Magma heating by decompression-driven crystallization beneath andesite volcanoes.” Nature: Letters. 443.7 (2006): 76-80. Researchgate.net. Web. 26 October 2018.