Final answer:
Scientists use signs such as ash plumes, changes in magnetic fields, ground deformation, seismic activity, and gas emissions to predict volcanic eruptions. They utilize satellite data to monitor magnetic orientation related to eruptions, although predictive capabilities are still being improved.
Step-by-step explanation:
Scientists look for various signs when predicting volcanic eruptions. One clear indicator is the observation of a plume of ash, like the one seen emanating from the Cleveland Volcano in the Aleutian Islands, which signifies active geological processes. However, predicting volcanic activities requires a more complex set of observations.
Some of the critical signs include changes in local magnetic fields, ground deformation, seismic activity, gas emissions, and changes in volcano topography. For instance, a positive correlation between variables, like the increase in the duration of geothermal eruptions and the time between them, can indicate an impending eruption. Advanced technologies such as satellites provide data on the magnetic orientation of the charged particles emitted by eruptions, which can affect the Earth's atmosphere. However, predictive capabilities in this area are still in development, and the orientation can only be accurately measured as the eruption impacts satellites positioned close to Earth.