People have a hard time wrapping their minds around the events and processes that change our planet, solar system, galaxy, or universe. How can we get an intuitive feel for a million years or a light year? The sizes of the events, duration of the processes, and the remote and inaccessible locations where the events and processes change things are so far beyond our experience that our imagination often stumbles when we try to get an intuitive grasp of their nature. A history of the volcanic events and the processes that lead to an eruption are often difficult to discover. A volcanic eruption is the result of melting events at depth in the Earth, beyond direct observation. After the melting events, disparate melt pockets may coalesce, changing the melt composition. Melts may interact with the surrounding rocks, changing the melt composition. Phases (solids, melts, and gases) may separate from the melt during ascent, changing the melt composition. Disentangling these several possible events and processes is the goal of volcanic petrologists, difficult or impossible such disentangling may be. Once in a while, though, luck smiles. The lava flows of the 1968 eruption of Kilauea Volcano, Hawai’i have characteristics consistent with the formation of an original magma in single melting event and which had minimal interaction with the surrounding rocks. The significant changes were caused be the separation of solid phases from successive magma bodies on ascent.
The original research was done years ago. The downloadable pdf file contains an account that I wrote a few years ago. The original research can be found in:
Nicholls J (2000) "Thermodynamics of a magmatic gas phase" 50 years later: Comments on a paper by John Verhoogen (1949). Canadian Mineralogist 38:1313-1328
Nicholls J, Stout MZ (1988) Picritic melts in Kilauea - Evidence from the 1967-1968 Halemaumau and Hiiaka eruptions. Journal of Petrology 29:1031-1057