People have worked out some ways to stop volcanoes erupting.
In 1919 Americans exploded dynamite in a Mexican volcano and released the pressure that was building in it. In 1943, American planes dropped two bombs in the crater of the volcano at Vesuvius in Italy and stopped it in its tracks.
Most volcanoes are, however, unstoppable. An eruption can last from a few seconds to a year, even centuries. Stromboli in Italy has erupted every few minutes over the last 2,000 years.
Some volcanoes erupt all the time. Most volcanoes erupt for three to four weeks and then rest. An eruption will stop naturally as soon as there is no more molten rock, when there is not enough gases in the magma, or when the chimney is plugged with cooled lava.
Human intervention is costly and is usually only attempted when many human lives would be lost if nothing was done.