Is It Possible To Prevent A Volcanic Eruption?

Yes it is. Volcanic eruptions are caused primarily by the buildup of gases under the earth's crust. This, coupled with a chamber of molten rock, or magma, are the ingredients and by-products of an eruption. But, it is the gaseous pressure that is the primary cause, at least of explosive eruptions. Non-explosive eruptions are more benign, and will not be considered.
By releasing the gas pressure beneath the earth's crust in a controlled manner, an explosive eruption can be averted. Underground magma cauldrons must be monitored as to their present condition. Uplifting of land is a sure sign of building pressure, as is occurring at Yellowstone Park presently, the site of one of two massive super-volcanoes known on earth. The eventual eruption of Yellowstone will obliterate life in a 50-mile radius, and cause massive disruption of the food chain for the entire globe for several years. Massive die-offs, including humans, will ensue.
The magma chamber may be carefully pierced, and the pressure relieved. Sooner is better. Small balloons don't pop with as much force as large balloons. Any such operation is naturally going to result in some amount of destructive force being released. The trade-off is that massive die-offs are averted. Nuclear weapons may be detonated underground as a last resort, although under tremendously high pressure situations these are bound to have grave consequences of their own.
It is imperative for the survival of humanity that experiments be undertaken immediately in order to develop techniques and knowledge in diffusing massive underground caldera. Experimentation on known low-pressure caldera will yield knowledge then applicable to more dire situations. Even the use of nuclear explosives, in the name of saving the human race, should not be shunned in this rush to gain vital knowledge. Knowing now is preferable to dying later.

Our technology cant prevent a volcano.The best we have is warning if a volcano is going to erupt.

By inserting huge thermocouples, or using glass as a heat transfer medium in a more conventional steam turbine power station, at geothermal hotspots it may be possible to extract the energy which supports the build up of pressure. Yielding a by-product called 'usable' energy. A Two birds one stone approach. It could be argued that without this type of approach to natural volcanism the human species is just sitting around until the next VEI 8.

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.

It depends on the volcano,as some may have secondary vents so exploding or blocking the main would do nothing more than cause it to explode sideways, like the eruption of mt st.helens,other respond well and are stoped, but only for a few years.

Not all the time but sometimes some countries might get lucky

No not really

Well it depends if you you are smart and you have studied on Volcanos and if so you might be able too.

I don't think so.You can't even predict volcanoes as some may go inactive and others may come out suddenly.However it is not safe living near volcanic region.

It's impossible because volcanos are part of nature. Nobody could stop nature.

Not unless you can find a virgin willing to jump into the volcano and appease the gods.

There are many theories as to how this could be done, but most of them would require things that we don't have access to!

I don't believe so.