When an oceanic tectonic plate and continental tectonic plate move toward each other and collide, they create subduction zone. The subduction zone is basically the boundary between the plates, where the oceanic plate slowly moves below the continental plate, gets into the mantle and is melted in it, thus destroyed. The oceanic plates are denser and heavier, but also lower and their crust is not as deep, while the continental plates are less dense and lighter, but higher and have much deeper crust. This results in the oceanic plate to move below the continental plate above it. The subduction zones create a lot of geological activity, and the earthquakes and volcanic activities are something that happens regularly. The volcanic island chains are mostly formed in close proximity to this type of boundaries, which we can easily see with the Pacific Ring of Fire.
