As the slab gets to a certain depth, it gets hot enough that it start to melt again. As it melts, it undergoes differentiation and also gets less dense. Low density means that it will start to rise back up again, usually, as granitic magma.
Living in the city is dangerous because there are dangerous people in the city, and it is very poluted, but in the country, it is more remote and less poluted then the city, hope this helps
