How large does the hole have to be for the magma to emerge?
Is this a trick question? Actually, despite the way lava flows look in pictures and movies, it is a lot more like cold molasses than water when it moves. Therefore, it doesn’t really flow that easily. If you turn a ketchup bottle upside down, the ketchup will probably not run out, but if you squeeze it (apply pressure to it), you get ketchup, and the more you squeeze the more you get. Rather than squeezing, you could also get ketchup by cutting the top off the bottle. Now what does this have to do with magma? Magma doesn’t flow easily, but it commonly is under high pressures—either from the weight of rocks around and above it, or from gases that build up inside it (think about what happens when you put your thumb over the top of a coke bottle and shake it up). That pressure can force magma into or through small cracks, or gas pressures can cause very large and explosive volcanic eruptions (like when you take your thumb off the top of that coke bottle you just shook up). Now, don’t go h
