Answer:
The May 18, 1980 eruptive column at Mount St. Helens fluctuated
in height through the day, but the eruption subsided by late
afternoon. By early May 19, the eruption had stopped. By that
time the ash cloud had spread to the central United States. Two
days later, even though the ash cloud had become more diffuse,
fine ash was detected by systems used to monitor air pollution
in several cities of the northeastern United States. Some of the
ash drifted around the globe within about 2 weeks.
