What escapes from magma during a quiet eruption?  

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Magma are the molten rocks beneath Earth's surface and escape during a volcanic eruption. The eruption can be quiet or violent depending on the gas content and viscosity. Gases are trapped in the magma and may form bubbles, depending on the vapor pressure of gas and the confining pressure of the rocks. Thee gases push the magma upwards in order to escape. Generally, quiet eruptions are observed for low viscosity magma containing less gases. Violent eruptions more common for high viscosity magma that contains more gases. When the magma reaches the Earth's surface, the trapped gases escape. This situation is very similar to the gas trapped with beverages (pepsi, coke, etc.). If you shake a sealed bottle and then open it, the pressurized gases will push the liquid along with them and rush towards the opening and escape. 

Thus, gases escape from the magma during a quiet eruption.

Hope this helps. 

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