When was the first volcanic eruption to be scientifically monitored as it happened?

Early eruptions were often witnessed and described, but not measured in the modern scientific sense. By the 19th century, volcanology became a formal field, and eruptions at places like Mount Vesuvius and Mount Etna were increasingly observed with instruments and systematic notes. This shift allowed scientists to track lava, ash, earthquakes, and gas emissions during eruptions rather than relying only on eyewitness accounts. The development of volcano observatories in the late 1800s marked the start of real-time scientific monitoring.