what causes this is down to pressure.The high as 45 kilometres (28 miles). As soon as it out，exploding magma， which is less dense than the rocks explodes out of the volcano， the magma turns into the air. around it，rises to the top of the volcano. into lava，which flows down the side of the As it grows， little pockets of gas begin to form mountain，where it cools and solidifies into and rise， much like in a bottle of fizzy drink. igneousrock. This increases the pressure inside the volcano Magma is nearly half oxygen and just over more and more， until eventually the pressure is one-quarter silicon， with aluminium， iron， unbearable and， just like when you take the lid calcium，sodium， potassium and magnesium off that fizzy drink， it explodes high into the making up most of the rest of it. Eruptions take place when water is present in the magma and sulphur-dioxide and carbon-dioxide bubbles form. The pressure increases and the water becomes less able to dissolve in the magma， so separates.That means there's an even higher concentration of gas bubbles in the magma. The magic number for an eruption is 75 per cent gas content，which is enough to force the magma up Volcanic eruptions are and out. among nature's most impressive spectacles The explosive process What happens when the The magic mark pressure gets too hot to handle? When the ratio of gas to magma is 3：1， the pressure becomes too much and the magma