Chapters 6 and 7 describe models that are used to quantify thermal emission from volcanic processes and the subsequent use of those results to quantify the movement of magma from the interior of a planet to the surface. This chapter demonstrates how different types of eruptions generate different thermal emission spectra, characteristic “thermal signatures” of eruption style, and how those spectra change with time. Determination of eruption style is important because it allows application of the appropriate model to determine effusion rate. Observed temporal behavior allows eruption mechanism to be constrained.

Because most ionian volcanic thermal-emission data are at resolutions rendering the entire emitting area sub-pixel, it is necessary to understand how eruption style affects the shape of the integrated thermal emission spectrum. Such analyses are dependent on, first, adequate spectral coverage and, second, temporal coverage. Spectral resolution need not be particularly high so long as data at appropriate wavelengths are available. Two wavelengths (2 μm and 5 μm are particularly effective) can be used to constrain the silicate volcanism mode because the resulting 2-μm to 5-μm ratio (2:5-μm ratio) is very sensitive to the changing surface temperatures of lava surfaces of ages ranging from seconds to months, sometimes to years (Davies and Keszthelyi, 2005). Table 8.1 shows the timescales of different volcanic processes and the instruments best suited to observe them.