Just a quick run down on each before we take a look at both.
Has to deal with who we are, what we think we are, who we want to be. It also has to deal with energy we feed our system, and the experiences in life that keeps us sane. In the chart is represents the area we feel is important, and as well as the father. It big fancy words, it’s The Ego.
Closest to the Sun, can only be Conjunct, or not as it can only be 28° away from each other. When in a conjunction to the Sun, or with in 5° of each other at least can cause a Burning Mercury, and it intensifies in exactitude. Or a Heavily aspected Mercury can also cause a Runaway Merc, since its integration in the System is something fierce.
Mercury is the way you perceive the world, and express those perceptions. Thought, memory, reading, writing, speaking, all forms of communication, electronic forms of communication, siblings, and your immediate environment.
So When you have a Burning Mercury, it’s when you get so interconnected with your ideas. Their Ego is entwined with their Thoughts. This causes them to associate their identity with their opinions. This is where they empower themselves through knowledge, and they really want their ideas to be important, or what they say to impact. This also leads to being narrow minded, because perception is subjective, and they have a hard time seeing outside the sphere for self, and do not realize that people can have different, and equally valid ideas.
Good analogy is the Story of Icarus, with his Wax wings, flying to close to the Sun, and falling.
Now a Runaway Merc, is when your Mercury is making a lot of aspects. This on its own it perfectly fine, however, that Mercurial energies can just run rampant, and a kid with ADHD having a free run in a Candy store. It’s going to be rampant, and it is going to devour as much as it can. Then in the end, it is going to be left with all this useless knowledge, and unless you are going to be trying out for Jeopardy, its going to be useless.
Think of it as being split into our different directions, but the one you need to go.
So these people, are amazing at trivia.
Over all it is not a bad thing, but it is definitely energy wasted.
So You could have a Burning Mercury through a tight conjunction, or a Runaway Merc, through a lot of aspects, or both.