At many volcanoes, clusters of small earthquakes can occur without any eruption, making it difficult to decide which signals reflect magma actually moving toward the surface. To improve eruption forecasts at a glacier-covered stratovolcano, a research team continuously measured two volcanic gases: carbon dioxide (CO2) and sulfur dioxide (SO2). The team noted that CO2 can escape from magma at greater depths than SO2 because CO2 separates from magma under higher pressures. The researchers therefore hypothesized that a sustained increase in the CO2-to-SO2 ratio would provide an earlier warning of an impending eruption than SO2 levels alone, since SO2 may not rise until magma reaches shallower levels.
Which finding, if true, would most directly support the researchers’ hypothesis?