Which event causes a volcanic eruption?

magma turning into lava
water being heated by magma
explosions occurring in magma chambers
magma cutting through older rocks

ANSWER:

When an explosion occurs in magma chambers, the volcano erupts. The buildup of pressure on the chamber lid breaks the lid forcing the magma out through the cracks to the atmosphere in full force.

EXPLANATION:

Deep inside the Earth's core, the temperature is extremely high. The layers of molten rocks on the core melt due to extremely high melting temperature and transform into magma. Magma contains different gases such as Sulphur dioxide, carbon dioxide, water vapor, etc. Magma along with the gases is sealed tightly in the magma chambers. As the magma begins to melt more rocks, the gases also expand increasingly, building huge pressure on the chamber lid. The chamber lid can no longer hold any more pressure and as a result, an eruption occurs.

Since wxyz is 4, halfof that would be 2.

Can you show the map?